Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The low
voltage-activated (T-type) Ca2+ channel has been implicated
in the regulation of aldosterone secretion from the adrenal zona
glomerulosa by extracellular K+ levels, angiotensin II, and
ACTH. However, the identity of the specific subtype mediating this
regulation has not been determined. We utilized in situ hybridization
to examine the distribution of three newly cloned members of the T-type
Ca2+ channel family, 1G,
1H,
and
1I, in the rat and bovine adrenal gland. Substantial
expression of only the mRNA transcript for the
1H-subunit was detected in the zona glomerulosa of both
rat and bovine. A much weaker expression signal was detected for the
1H transcript in the zona fasciculata of bovine. Whole
cell recordings of isolated bovine adrenal zona glomerulosa cells
showed the native low voltage-activated current to be inhibited by
NiCl2 with an IC50 of 6.4 ± 0.2 µM.
Because the
1H subtype exhibits similar NiCl2 sensitivity, we propose that the
1H
subtype is the predominant T-type Ca2+ channel present in
the adrenal zona glomerulosa.
in situ hybridization; adrenal cortex; low voltage-activated calcium channels; nickel inhibition
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
THE THREE CONCENTRIC ZONES within the cortex of the mammalian adrenal gland were first described as the zona glomerulosa, zona fasciculata, and zona reticularis in 1866 by Arnold (2). These three zones have different functional roles in steroid hormone production: mineralocorticoids are produced in the zona glomerulosa, glucocorticoids in the zona fasciculata, and C19 steroids in the zona reticularis (32). In the zona glomerulosa, aldosterone secretion is regulated by adrenocorticotropin (ACTH), angiotensin II (ANG II), and K+ in a Ca2+-dependent manner (1, 11).
Agonist-stimulated and plasma [K+] regulation of aldosterone secretion in the zona glomerulosa is dependent on changes in membrane potential (24, 25, 29, 30) and the influx of extracellular Ca2+ (5, 14, 15). Because small elevations in extracellular [K+] would be expected to increase low voltage-activated (LVA), T-type Ca2+ channel currents in rat and bovine adrenal glomerulosa cells preferentially (6, 31, 33), LVA Ca2+ channels may provide the link between small depolarizations in membrane potential and the influx of extracellular Ca2+. The low voltage of activation and slow deactivation kinetics of the LVA Ca2+ channel make it ideally suited to maximize the amount of Ca2+ entry at depolarized membrane potentials, where channel inactivation may be incomplete, and thus provide a sensor for coupling minimal changes in membrane potential to prolonged influxes of Ca2+. Such biophysical properties of LVA Ca2+ channels would allow them to facilitate a prolonged Ca2+ influx to sustain the secretion of aldosterone from the zona glomerulosa.
Recently, three separate members of the T-type Ca2+ channel
family have been cloned from human and rat tissues (8, 17, 26,
27) . The 1G,
1H, and
1I subtypes all exhibit currents characteristic of
native T-type channels when expressed in HEK-293 cells or oocytes.
However, the
1H subtype has been shown to be inhibited
by low micromolar concentrations of NiCl2 (<10 µM), distinguishing it from the
1G and
1I
subtypes, which typically require >100 µM NiCl2 for
inhibition (18). Furthermore, recent work using in situ
hybridization indicated that the mRNA expression for the three subtypes
each exhibited unique and complementary distribution patterns
throughout the rat central and peripheral nervous systems
(36). The subtype that contributes to LVA activity in the
zona glomerulosa is not known.
We have set out to identify which of the three T-type Ca2+
channel subtypes are present throughout the rat and bovine adrenal gland. In situ hybridization studies in rat and bovine adrenal tissue
indicated predominant expression of mRNA for the 1H
subtype. In the rat adrenal, detectable levels of
1H
mRNA were localized exclusively to the outer cortical regions that
circumscribed the zona glomerulosa, while
1H mRNA was
detected in both the zona glomerulosa and zona fasciculata of the
bovine adrenal gland. In addition, whole cell voltage-clamp recordings
of T-type Ca2+ channel currents from isolated bovine zona
glomerulosa cells displayed a high sensitivity to low micromolar
concentrations of NiCl2. Together, these data indicate that
the
1H subtype is the predominant LVA Ca2+
channel expressed in the zona glomerulosa of the rat and bovine adrenal.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Tissue preparation.
Male Sprague-Dawley rats (250-350 g) were anesthetized with
ketamine/xylazine before surgical removal of the adrenal gland or
decapitation and removal of the brain. Adrenal glands and brains were
immediately frozen on dry ice, cut into 10-µm-thick sections, thaw
mounted onto charged slides (Superfrost Plus; Fisher Scientific, Houston, TX), and stored at 80°C for later use. Two- to
four-day-old calf adrenal glands (Florida Biologicals) were obtained
immediately after slaughter, cleaned of adherent fat, frozen on dry
ice, and cut into 10-µm-thick sections. The sections were thaw
mounted onto charged slides and stored at
80°C for
later use. Pretreatment of the slides before hybridization was
described previously (36). In short, slides were allowed to equilibrate for ~5 min before they were fixed in a fresh 4% paraformaldehyde solution. The slides were then subjected to a series
of washes in 0.1 M PBS (pH 7.4), a 5-min treatment with glycine (0.2%
in 0.1 M PBS), and a 10-min treatment with acetic anhydride (0.25% in
0.1 M triethanolamine, 0.9% NaCl, pH 8) before undergoing dehydration
and delipidation effected by a series of increasing ethanol washes. The
hybridization reaction was carried out overnight at 37°C
in the presence of a hybridization buffer containing 50% formamide, 600 mM NaCl, and 60 mM standard sodium citrate (SSC), 1× Denhardt's solution (Sigma), 10% dextran sulfate, 100 mM dithiothreitol, 250 µg/ml yeast tRNA, and 1 mg/ml salmon sperm DNA. The slides were then
subjected to a series of four 15-min washes in SSC at 55°C, followed by a 1-h wash in SSC at room temperature.
Oligonucleotide probes.
The rationale and design of the rat-specific oligonucleotide probes
were described previously (36). In short, 33-bp antisense probes were designed to detect the I-II cytoplasmic loop for each of
the three T-type Ca2+ channel gene products. The I-II
cytoplasmic loop contains a much lower degree of sequence similarity
than the transmembrane region and enables the design of probes specific
to each gene transcript (8). Multiple probes recognizing
different regions in the I-II loop were designed for each subtype to
confirm individual probe effectiveness. The probes listed in Table
1 demonstrated specific binding and were
used either alone (see Fig. 1) or in combination (see Fig. 3). For the
bovine study, 33-mer bovine-specific probes were made containing 1- or
2-bp mismatches with the corresponding region of the rat sequence. The
mismatches provide an internal control for the effectiveness of each
probe by examining their distribution under described conditions,
specifically the rat brain (36). Additional probes were
designed specific to the bovine tyrosine hydroxylase gene and the
bovine CYP11B gene. These controls provided a positive
indication of successful hybridization along with morphological
indication of cellular phenotype in the tissue preparations.
Competition experiments utilizing an ~1,000-fold excess of unlabeled
probe were used to assay the nonspecific interaction associated with
each probe. Probe sequences were checked against sequences in the
GenBank to ensure no cross-reactivity with other Ca2+
channel gene products or other sequences in the database. Probes were
labeled with [33P]dATP (NEN) by using terminal
deoxyribonucleotidyl transferase (Life Technologies, Gaithersburg, MD)
and were purified by ethanol precipitation. The sequences for the
probes used in this study are listed in Table 1.
|
|
Sequencing of I-II loop.
Total RNA was isolated and reverse transcribed to cDNAs from bovine
adrenal glomerulosa cells and bovine brain cerebellum. A set of
degenerate PCR primers for all subtypes was designed to specifically
recognize the highly conserved transmembrane regions flanking the I-II
loop (Table 1). PCR products were then subcloned into the TA cloning
vector pCR2.1 (Invitrogen, Carlsbad, CA) before transformation into
competent cells (INVFt, Invitrogen). Positive clones
were detected by color and identified through restriction enzyme digest
before sequencing. I-II loop sequences were then compared with their
human isoforms for identification purposes.
Cell isolation. Neonatal bovine adrenal glomerulosa cells were isolated by collagenase digestion, as described previously (12, 19, 20). The glomerulosa layer was carefully cut away from the adrenal cortex into thin sections and stored in a Ca2+/BSA-free standard Krebs-Ringer bicarbonate (KRB) buffer containing (in mM) 120 NaCl, 25 NaHCO3, 3.5 KCl, 1.2 MgSO4, 1.2 NaH2PO4, and 0.1% dextrose, equilibrated with 95% air-5% CO2 (pH 7.4). The slices were digested twice at 37°C for 10 min with collagenase (160 U/mg; Worthington, Freehold, NJ) before being mechanically dispersed, purified through a 20-µm nylon mesh (Tetko, Elmsford, NY), recovered by centrifugation, and resuspended in KRB containing 1.25 mM CaCl2 and 0.2% BSA. A discontinuous (30%/56%) Percoll gradient (Pharmacia, Piscataway, NJ) was used to further purify the cells before they were resuspended in the Ca2+/BSA KRB. Isolated cells were then stored overnight in a 50:50 DMEM/F-12:KRB (2 mM K+) solution. For recording, cells were plated directly onto collagen-coated slides (50 µg/ml in 0.2 N acetic acid; Becton Dickinson, Bedford, MA) in 1:1 DMEM/F-12 medium with 100 U/ml penicillin and 100 µg/ml streptomycin ~3 h before experimentation.
Patch-clamp experiments.
Electrophysiology experiments were carried out as described previously
(19, 20). Briefly, Ca2+ currents were recorded
from single adrenal glomerulosa cells (12-18 µm) adhered to
collagen-coated slides. The slides were placed into a 500-µl
microincubator chamber perfused by gravity at a rate of 0.5 ml/min with
an external bath solution containing (in mM) 134 tetraethylammonium
chloride, 10 CaCl2, 0.5 MgCl2, 5 dextrose, 32 sucrose, and 10 HEPES-Cs (filtered, pH 7.4). Patch pipettes (2-4
M) were made from 0010 glass capillaries (World Precision
Instruments, Sarasota, FL) by using an L/M-3P-A vertical puller (List
Medical Electronic, Darmstadt, Germany). The standard internal pipette
solution contained (in mM) 115 CsCl, 1 tetrabutylammonium chloride, 11 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, 0.9 CaCl2, 1 MgCl2, 20 HEPES, 5 MgATP,
and 1 LiGTP (pH 7.2). Whole cell currents were recorded with
the use of an Axopatch 200A amplifier and pCLAMP 6.0 software (Axon
Instruments) by applying a 10.4-ms test pulse to
15 mV from a holding
potential of
90 mV. Tail currents were elicited by a 28-ms
repolarization step to
70 mV and recorded. Currents were sampled at
12.5 kHz and filtered with an eight-pole low-pass Bessel filter
(Frequency Devices, Haverhill, MA) set to a cutoff frequency of 2 kHz.
Ni2+ inhibition experiments were performed by exchange of
the bath solution with standard external solution containing increasing concentrations of NiCl2 (stock 100 mM). Currents were
allowed to stabilize before the Ni2+ concentration was
incremented in the perfusate.
Data analysis.
In situ hybridization slides were exposed to autoradiographic film
(Hyperfilm -max or Hyperfilm H3; Amersham, Arlington
Heights, IL) for either 5 or 10 days. Autoradiographs were digitally
captured with a DAGE-16E microscope mounted to a light box. Images were
manipulated collectively as a group in Adobe Photoshop (Adobe Systems).
![]() |
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1H subtype of the LVA
Ca2+ channel family is
expressed in the zona glomerulosa of rat adrenal tissue.
Prominent LVA currents have been recorded in rat adrenal cortical cell
preparations that contain a mixture of aldosterone-producing glomerulosa cells and corticosterone-producing fasciculata cells (9, 21, 25, 29, 30). In situ hybridization studies were
carried out to determine the subtype-specific expression and
localization of members of the LVA Ca2+ channel family in
rat adrenal tissue. High levels of
1H mRNA expression
were readily detectable in the rat adrenal in contrast to extremely low
levels of mRNA expression for the
1G subtype and a
virtual absence of mRNA expression for the
1I subtype
(Fig. 1, left). The
distribution of the
1H message was limited to the outer
region of the cortical layer of the tissue; however, exact zonal distribution could not be determined. Cold competition
experiments utilizing a 1,000-fold excess of unlabeled probe reduced
the intensity of the strong
1H signal and the weak
1G signal equivalently, indicating that the interactions
were specific for each mRNA transcript (Fig. 1, right).
Sequencing of the putative I-II loop of the three
members of the bovine LVA
Ca2+ channel family.
The detected dominant expression of 1H LVA channel mRNA
in the zona glomerulosa of the rat prompted us to determine the
expression pattern in the bovine adrenal gland, where LVA currents have
been characterized in cell preparations containing exclusively cells from the zona glomerulosa (6, 22, 28, 34). Preliminary experiments were conducted with rat-specific oligonucleotides because
sequence information for the bovine family of LVA Ca2+
channels was not available from GenBank. However, these rat probes could not identify message for any member of the LVA channel family in
bovine adrenal tissue, prompting us to sequence the I-II loop for each
paralog of the bovine channel family. cDNA was prepared by reverse
transcription of total RNA from isolated bovine adrenal zona
glomerulosa cells and bovine cerebellum. A set of degenerate PCR
primers (Table 1) was designed to recognize highly conserved sequences
in transmembrane regions flanking the I-II loop. These primers
hybridized with sequences across LVA family members as well as across
species. PCR products were subcloned into TA cloning vector, and
restriction enzyme digests identified positive clones. Thirteen
positive clones, identified by color, were sequenced and identified as
the bovine variant of the
1H. Only PCR product for the
1H channel was detected in bovine adrenal glomerulosa cells (data not shown). The I-II loop sequences for
1G
and
1I were obtained from bovine cerebellum RNA, which
has been shown by previous work to express these two family members in
the rat (36). Clearly, the identification of mRNA for all
three subtypes with the use of our degenerate primers attests to the
efficacy of the primer design strategy. The sequences for the putative I-II loop of the three members of the T-type Ca2+ channel
family in bovine are listed in Fig.
2A. A
dendrogram indicating sequence homology between the bovine family
members and their respective human or rat counterparts within the I-II loop is shown in Fig. 2B. The relatively low degree of
homology within this loop among the members of the LVA Ca2+
channel family provided regions from which to design probes specific to
each subtype.
|
Bovine adrenal tissue expresses the
1H subtype of the T-type
Ca2+ channel family.
Antisense oligonucleotide probes specific to the three members of the
bovine LVA Ca2+ channel family were designed from the
sequences of their putative I-II loops, listed in Fig. 2. Figure
3 displays the autoradiographs from an in
situ hybridization study designed to detect and localize the
channel-specific expression of the three members of the LVA Ca2+ channel family. Figure 3, left, depicts
1G,
1H, and
1I mRNA expression in addition to mRNA expression for the cellular phenotype markers tyrosine hydroxylase and CYP11B. Tyrosine hydroxylase is
present in dopamine-producing cells in the medulla of the bovine adrenal gland, while CYP11B is a multifunctional P-450
enzyme that catalyzes either the formation of aldosterone or cortisol from corticosterone in either the zona glomerulosa or zona fasciculata of the bovine adrenal cortex, respectively (32). These
markers allowed us to localize the mRNA signal to a specific zonal
region within the bovine adrenal gland. As in the rat adrenal gland, the predominant subtype-specific expression was limited to the
1H transcript.
1H probes identified two
regions with markedly different levels of message abundance in the
bovine adrenal gland (Fig. 3). The predominant expression signal was
present near the outer cortical region of the adrenal tissue, while a
much weaker signal was present within the cortex just proximal to this
area of expression. On the basis of the distribution signal of the marker enzyme CYP11B, the
1H transcript is expressed
predominantly in the zona glomerulosa with lower levels of expression
confined to the zona fasciculata. The detection of
1H
message in the zona fasciculata is consistent with previously reported
electrophysiological data indicating T-type Ca2+
channel activity in both the zona glomerulosa and the zona fasciculata in the bovine adrenal gland (6, 10, 22, 23, 28, 37).
|
T-type Ca2+ currents recorded from
isolated bovine adrenal zona glomerulosa cells exhibit
Ni2+ sensitivity.
To determine whether these data indicating high levels of
1H mRNA correlate with the expression of functional
channel protein, we took advantage of the differential Ni2+
sensitivity of the LVA Ca2+ currents from expressed T-type
channel clones. After heterologous expression, the
1H
subtype exhibits a much greater sensitivity to inhibition by
NiCl2 (IC50 ~10 µM of blockable current
component) than either the
1G or
1I
subtype (IC50 ~200-300 µM) (18). Thus
we performed whole cell voltage-clamp recordings of zona glomerulosa
cells in the presence of increasing concentrations of
NiCl2. T-type Ca2+ currents were elicited with
a test pulse from
90 mV to
15 mV upon repolarization to
70 mV. Exponential fits to the tail currents elicited upon
repolarization were used to measure the effect of Ni2+ on
LVA channel activity. Figure
4A displays representative
current tracings from a single cell recorded in the presence of
increasing [Ni2+]. The LVA current was almost completely
abolished by as little as 100 µM Ni2+. The dose
dependence of Ni2+ inhibition is shown in Fig.
4B. Clearly, the LVA current present in the zona glomerulosa
cells was blocked by low micromolar concentrations of Ni2+.
The IC50 for NiCl2 inhibition was calculated to
be 6.4 ± 0.2 µM with a Hill slope of
1.14 ± 0.05 (n = 7-11). This sensitivity to low micromolar
concentrations compares with the IC50 for
1H currents heterologously expressed in HEK-293 cells (12 µM) and indicates a functional role for the
1H subtype in the
adrenal zona glomerulosa. However, at 100 µM [Ni2+],
only ~80% of the measured current was inhibited by Ni2+.
Incomplete block by Ni2+ of
1H current at a
low IC50 is consistent with cloned Ca2+ channel
data of our own (unpublished observations) and others (17)
showing that a component of
1H current remains
uninhibited. At higher concentrations block of Ca2+ current
by Ni2+ is no longer diagnostic of LVA Ca2+
channel subtypes because high voltage-activated Ca2+
channel subtypes are inhibited with IC50 values similar to
those reported for
1G and
1I LVA channels
(39). Thus, when Ni2+ is used, it is not
possible to assign the residual component of current in the bovine
glomerulosa cell to a specific channel subtype. Nevertheless, the in
situ hybridization results coupled with the electrophysiological data
from isolated zona glomerulosa cells indicate that the
1H subtype is the predominant T-type Ca2+
channel active in the zona glomerulosa of the bovine adrenal.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The T-type Ca2+ channel plays an important role in
adrenal zona glomerulosa physiology. Molecular identification of the
members of the T-type Ca2+ channel family has facilitated
our study of the identity of the subtypes expressed in the adrenal zona
glomerulosa. Using in situ hybridization, we demonstrate that the
1H subtype is the predominant LVA Ca2+
channel present in the rat adrenal cortex, presumably within the zona
glomerulosa. Furthermore, electrophysiological data coupled with in
situ hybridization studies indicate that the
1H subtype is also the predominant LVA channel in the bovine zona glomerulosa. In
both species, substantially lower levels of
1G mRNA
transcript were detected, indicating region-specific expression of the
different LVA Ca2+ channel subtypes. This finding is
consistent with a report describing differential distributions of the
LVA family members in the central nervous system as well
(36).
A role for the influx of Ca2+ during steroidogenesis and
aldosterone secretion from the zona glomerulosa has been purported for
several years (1, 4, 11, 35). In fact, the presence of LVA
channel activity in the zona glomerulosa of the rat and bovine is well
documented (6, 9, 21, 22, 25, 29, 30, 34). These currents
are similar to T-type currents described in neuronal systems, which can
be characterized by their distinct half-activation potential, rapid
inactivation, slow deactivation, and small single-channel conductance
(13). Our demonstration of the predominant expression of
1H mRNA in the zona glomerulosa of both the rat and
bovine provides a molecular identity to the LVA current active in
mediating aldosterone secretion. However, the role of the LVA
Ca2+ channel in cortisol secretion from the zona
fasciculata is less clear. Several reports have identified
voltage-dependent Ca2+ currents in isolated bovine
fasciculata cells (10, 23, 37), in contrast to rat
fasciculata cells, where their presence has been excluded (37,
38). One exception, however, is a study demonstrating small LVA
currents in freshly isolated cells that are lost within 1 day of cell
culture (3). Nonetheless, these currents displayed the
distinct half-activation potential, rapid inactivation, slow
deactivation, and small single-channel conductance described for T-type
currents in other systems. Our in situ hybridization results coincide
with the majority of previous observations in that mRNA for the
1H subtype was detected in the zona fasciculata of the
bovine but not in that of the rat. However, we cannot conclusively rule
out T-type Ca2+ channel activity in the rat fasciculata
because morphological characterization of the zonation of the rat
adrenal was not carried out.
Even though we have shown that the 1H subtype is the
predominant LVA channel present in the zona glomerulosa, it is also probable that the
1G subtype is present as well, because
low levels of the
1G subtype were detected in our in
situ hybridization studies. The biophysical properties of the cloned
1G and
1H channels appear to be
remarkably similar. Both channels, when expressed in oocytes or HEK-293
cells, respectively, open near resting membrane potential, inactivate
rapidly, exhibit slow deactivation, and have small unitary conductances
(7, 8, 27). However, recently Kozlov et al.
(16) demonstrated that the cloned subtypes exhibit
distinct kinetics of Ca2+ entry in response to different
action potential frequencies and duration. Even though action
potentials do not play a role in aldosterone secretion from the zona
glomerulosa, the differences in Ca2+ entry through each
subtype may induce different signaling patterns that uniquely alter
cell physiology. Furthermore, while the
1G and
1H subtypes contain ~90% sequence identity across
their transmembrane-spanning regions, the intracellular loops and amino
and carboxy termini exhibit a much wider divergence in sequence
similarity, making these regions potential targets for differential
regulation (7).
This disproportionate expression pattern, distinct kinetics of
Ca2+ entry during mock action potentials, and
highly divergent intracellular loops and termini for the
1G and
1H LVA Ca2+ channels
could allow the channels to either subserve different functional roles
in various systems or mediate the same function under different modes
of regulation. Our laboratory has demonstrated that LVA
Ca2+ channel current in bovine zona glomerulosa cells is,
in fact, regulated by calmodulin-dependent protein kinase II activity
(20). This kinase increases the frequency of channel
opening at negative membrane potentials, which results in a shift in
the half-activation potential of the channel to more hyperpolarized
potentials. Such a shift would increase the ability of the cell to
respond with an increase in aldosterone secretion to even smaller
changes in membrane potential and could account for the high
sensitivity of the adrenal zona glomerulosa cell to relatively small
fluctuations in external [K+] or physiological
concentrations of hormonal agonists. If mechanisms for LVA
Ca2+ channel regulation are indeed subtype specific, then
one would ultimately expect differences in aldosterone secretion based
on specific Ca2+ channel subtype expression, i.e.,
differences in cellular physiology could be accounted for by
differences in T-type Ca2+ channel expression. The
validation of these predictions awaits future experimentation.
![]() |
ACKNOWLEDGEMENTS |
---|
We thank Dr. Douglas A. Bayliss for experimental guidance and input during the development of this project.
![]() |
FOOTNOTES |
---|
This work was supported by National Heart, Lung, and Blood Institute Grant HL-36977 (to P. Q. Barrett).
Address for reprint requests and other correspondence: P. Q. Barrett, Dept. of Pharmacology, Univ. of Virginia Health System, PO Box 800735, 1300 Jefferson Park Ave., Charlottesville, VA 22908-0735 (E-mail: pqb4b{at}virginia.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 28 March 2000; accepted in final form 12 September 2000.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Aguilera, G,
and
Catt KJ.
Participation of voltage-dependent calcium channels in the regulation of adrenal glomerulosa function by angiotensin II and potassium.
Endocrinology
118:
112-118,
1986[Abstract].
2.
Arnold, J.
Ein Betrag zu der feiner Struktur und dem Chemismus der Nebennieren.
Arch Pathol Anat Physiol Klin Med
35:
64-107,
1866.
3.
Barbara, JG,
and
Takeda K.
Voltage-dependent currents and modulation of calcium channel expression in zona fasciculata cells from rat adrenal gland.
J Physiol (Lond)
488:
609-622,
1995[Abstract].
4.
Barrett, PQ,
Bollag WB,
Isales CM,
McCarthy RT,
and
Rasmussen H.
Role of calcium in angiotensin II-mediated aldosterone secretion.
Endocr Rev
10:
496-518,
1989[ISI][Medline].
5.
Capponi, AM,
Lew PD,
Jornot L,
and
Vallotton MB.
Correlation between cytosolic free Ca2+ and aldosterone production in bovine adrenal glomerulosa cells. Evidence for a difference in the mode of action of angiotensin II and potassium.
J Biol Chem
259:
8863-8869,
1984
6.
Cohen, CJ,
McCarthy RT,
Barrett PQ,
and
Rasmussen H.
Ca channels in adrenal glomerulosa cells: K+ and angiotensin II increase T-type Ca channel current.
Proc Natl Acad Sci USA
85:
2412-2416,
1988[Abstract].
7.
Cribbs, LL,
Gomora JC,
Daud AN,
Lee J,
and
Perez-Reyes E.
Molecular cloning and functional expression of ca(v)31c, a T-type calcium channel from human brain.
FEBS Lett
466:
54-58,
2000[ISI][Medline].
8.
Cribbs, LL,
Lee JH,
Yang J,
Satin J,
Zhang Y,
Daud A,
Barclay J,
Williamson MP,
Fox M,
Rees M,
and
Perez-Reyes E.
Cloning and characterization of alpha1H from human heart, a member of the T-type Ca2+ channel gene family.
Circ Res
83:
103-109,
1998
9.
Durroux, T,
Gallo-Payet N,
and
Payet MD.
Three components of the calcium current in cultured glomerulosa cells from rat adrenal gland.
J Physiol (Lond)
404:
713-729,
1988[Abstract].
10.
Enyeart, JJ,
Mlinar B,
and
Enyeart JA.
T-type Ca2+ channels are required for adrenocorticotropin-stimulated cortisol production by bovine adrenal zona fasciculata cells.
Mol Endocrinol
7:
1031-1040,
1993[Abstract].
11.
Fakunding, JL,
Chow R,
and
Catt KJ.
The role of calcium in the stimulation of aldosterone production by adrenocorticotropin, angiotensin II, and potassium in isolated glomerulosa cells.
Endocrinology
105:
327-333,
1979[ISI][Medline].
12.
Fern, RJ,
Hahm MS,
Lu HK,
Liu LP,
Gorelick FS,
and
Barrett PQ.
Ca2+/calmodulin-dependent protein kinase II activation and regulation of adrenal glomerulosa Ca2+ signaling.
Am J Physiol Renal Fluid Electrolyte Physiol
269:
F751-F760,
1995
13.
Huguenard, JR.
Low-threshold calcium currents in central nervous system neurons.
Annu Rev Physiol
58:
329-348,
1996[ISI][Medline].
14.
Kojima, I,
Kojima K,
and
Rasmussen H.
Role of calcium fluxes in the sustained phase of angiotensin II- mediated aldosterone secretion from adrenal glomerulosa cells.
J Biol Chem
260:
9177-9184,
1985
15.
Kojima, I,
and
Ogata E.
Direct demonstration of adrenocorticotropin-induced changes in cytoplasmic free calcium with aequorin in adrenal glomerulosa cell.
J Biol Chem
261:
9832-9838,
1986
16.
Kozlov, AS,
McKenna F,
Lee JH,
Cribbs LL,
Perez-Reyes E,
Feltz A,
and
Lambert RC.
Distinct kinetics of cloned T-type Ca2+ channels lead to differential Ca2+ entry and frequency-dependence during mock action potentials.
Eur J Neurosci
11:
4149-4158,
1999[ISI][Medline].
17.
Lee, JH,
Daud AN,
Cribbs LL,
Lacerda AE,
Pereverzev A,
Klockner U,
Schneider T,
and
Perez-Reyes E.
Cloning and expression of a novel member of the low voltage-activated T- type calcium channel family.
J Neurosci
19:
1912-1921,
1999
18.
Lee, JH,
Gomora JC,
Cribbs LL,
and
Perez-Reyes E.
Nickel block of three cloned T-type calcium channels: low concentrations selectively block alpha1H.
Biophys J
77:
3034-3042,
1999
19.
Lu, HK,
Fern RJ,
Luthin D,
Linden J,
Liu LP,
Cohen CJ,
and
Barrett PQ.
Angiotensin II stimulates T-type Ca2+ channel currents via activation of a G protein, Gi.
Am J Physiol Cell Physiol
271:
C1340-C1349,
1996
20.
Lu, HK,
Fern RJ,
Nee JJ,
and
Barrett PQ.
Ca2+-dependent activation of T-type Ca2+ channels by calmodulin-dependent protein kinase II.
Am J Physiol Renal Fluid Electrolyte Physiol
267:
F183-F189,
1994
21.
Matsunaga, H,
Maruyama Y,
Kojima I,
and
Hoshi T.
Transient Ca2+-channel current characterized by a low-threshold voltage in zona glomerulosa cells of rat adrenal cortex.
Pflügers Arch
408:
351-355,
1987[ISI][Medline].
22.
Matsunaga, H,
Yamashita N,
Maruyama Y,
Kojima I,
and
Kurokawa K.
Evidence for two distinct voltage-gated calcium channel currents in bovine adrenal glomerulosa cells.
Biochem Biophys Res Commun
149:
1049-1054,
1987[ISI][Medline].
23.
Mlinar, B,
Biagi BA,
and
Enyeart JJ.
Voltage-gated transient currents in bovine adrenal fasciculata cells I T-type Ca2+ current.
J Gen Physiol
102:
217-237,
1993[Abstract].
24.
Natke, E, Jr,
and
Kabela E.
Electrical responses in cat adrenal cortex: possible relation to aldosterone secretion.
Am J Physiol Endocrinol Metab Gastrointest Physiol
237:
E158-E162,
1979
25.
Payet, MD,
Benabderrazik M,
and
Gallo-Payet N.
Excitation-secretion coupling: ionic currents in glomerulosa cells: effects of adrenocorticotropin and K+ channel blockers.
Endocrinology
121:
875-882,
1987[Abstract].
26.
Perez-Reyes, E.
Three for T: molecular analysis of the low voltage-activated calcium channel family.
Cell Mol Life Sci
56:
660-669,
1999[ISI][Medline].
27.
Perez-Reyes, E,
Cribbs LL,
Daud A,
Lacerda AE,
Barclay J,
Williamson MP,
Fox M,
Rees M,
and
Lee JH.
Molecular characterization of a neuronal low-voltage-activated T-type calcium channel.
Nature
391:
896-900,
1998[ISI][Medline].
28.
Quinn, SJ,
Brauneis U,
Tillotson DL,
Cornwall MC,
and
Williams GH.
Calcium channels and control of cytosolic calcium in rat and bovine zona glomerulosa cells.
Am J Physiol Cell Physiol
262:
C598-C606,
1992
29.
Quinn, SJ,
Cornwall MC,
and
Williams GH.
Electrical properties of isolated rat adrenal glomerulosa and fasciculata cells.
Endocrinology
120:
903-914,
1987[Abstract].
30.
Quinn, SJ,
Cornwall MC,
and
Williams GH.
Electrophysiological responses to angiotensin II of isolated rat adrenal glomerulosa cells.
Endocrinology
120:
1581-1589,
1987[Abstract].
31.
Quinn, SJ,
and
Williams GH.
Regulation of aldosterone secretion.
Annu Rev Physiol
50:
409-426,
1988[ISI][Medline].
32.
Rainey, WE.
Adrenal zonation: clues from 11-hydroxylase and aldosterone synthase.
Mol Cell Endocrinol
151:
151-160,
1999[ISI][Medline].
33.
Rossier, MF,
Burnay MM,
Maturana A,
and
Capponi AM.
Duality of the voltage-dependent calcium influx in adrenal glomerulosa cells.
Endocr Res
24:
443-447,
1998[ISI][Medline].
34.
Rossier, MF,
Python CP,
Capponi AM,
Schlegel W,
Kwan CY,
and
Vallotton MB.
Blocking T-type calcium channels with tetrandrine inhibits steroidogenesis in bovine adrenal glomerulosa cells.
Endocrinology
132:
1035-1043,
1993[Abstract].
35.
Spat, A,
Enyedi P,
Hajnoczky G,
and
Hunyady L.
Generation and role of calcium signal in adrenal glomerulosa cells.
Exp Physiol
76:
859-885,
1991[ISI][Medline].
36.
Talley, EM,
Cribbs LL,
Lee JH,
Daud A,
Perez-Reyes E,
and
Bayliss DA.
Differential distribution of three members of a gene family encoding low voltage-activated (T-type) calcium channels.
J Neurosci
19:
1895-1911,
1999
37.
Yanagibashi, K,
Kawamura M,
and
Hall PF.
Voltage-dependent Ca2+ channels are involved in regulation of steroid synthesis by bovine but not rat fasciculata cells.
Endocrinology
127:
311-318,
1990[Abstract].
38.
Yanagibashi, K,
Papadopoulos V,
Masaki E,
Iwaki T,
Kawamura M,
and
Hall PF.
Forskolin activates voltage-dependent Ca2+ channels in bovine but not in rat fasciculata cells.
Endocrinology
124:
2383-2391,
1989[Abstract].
39.
Zamponi, GW,
Bourinet E,
and
Snutch TP.
Nickel block of a family of neuronal calcium channels: subtype and subunit-dependent action at multiple sites.
J Membr Biol
151:
77-90,
1996[ISI][Medline].