Department of Neurobiology, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The objective of this study was to
determine the relative contribution of Cl channels to
volume regulation of cultured rat cortical astrocytes after hypotonic
cell swelling. Using a Coulter counter, we showed that cortical
astrocytes regulate their cell volume by ~60% within 45 min after
hypotonic challenge. This volume regulation was supported when
Cl
was replaced with Br
,
NO
, or
acetate
but was inhibited when Cl
was
replaced with isethionate
or gluconate
.
Additionally, substitution of Cl
with I
completely blocked volume regulation. Volume regulation was unaffected by furosemide or bumetanide, blockers of KCl transport, but was inhibited by Cl
channel blockers, including
5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB),
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and niflumic
acid. Surprisingly, the combination of Cd2+ with NPPB,
DIDS, or niflumic acid inhibited regulation to a greater extent than
any of these drugs alone. Volume regulation did not differ among
astrocytes cultured from different brain regions, as cerebellar and
hippocampal astrocytes exhibited behavior identical to that of cortical
astrocytes. These data suggest that Cl
flux through ion
channels rather than transporters is essential for volume regulation of
cultured astrocytes in response to hypotonic challenge.
glia; ion channels; Coulter counter
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
MOST CELLS POSSESS MECHANISMS to control or regulate their volume (18), and volume regulation has been clearly demonstrated for cultured rat cortical astrocytes in response to hypotonic challenge (14, 25). However, it appears that the mechanisms of volume regulation are ineffective in astrocytes in the brain after neurological insult, as swelling of astrocytes is a major complicating factor of conditions including ischemia, trauma, hyponatremia, and hepatic encephalopathy (16). Astrocytic swelling can decrease the volume of the extracellular space and have dramatic consequences on diffusion of neurotransmitters and on excitability (13). Additionally, swelling can have deleterious consequences on normal astrocytic functions such as K+, pH, amino acid, and transmitter homeostasis (12). Therefore, an impetus exists to provide a detailed assessment of the specific mechanisms that control cell volume in cultured cortical astrocytes, as this may provide insight into the persistence of astrocytic swelling in the brain.
In astrocytes, as in many other cell types, a significant body of
evidence supports the notion that at least two mechanisms contribute to
volume regulation in response to hypotonic challenge, namely, the
efflux of inorganic ions such as K+ or Cl and
the release of organic osmolytes such as taurine (for review see Ref.
32). Pasantes-Morales and colleagues (26)
suggested that these two mechanisms contribute approximately equally to volume regulation of cortical astrocytes. Less clear, however, are the
pathways for osmolyte and Cl
release. Both inorganic and
organic ions may be released through ion channels, such as
volume-sensitive organic osmolyte-anion channels (VSOAC) (9,
10). Alternatively, organic osmolytes may be released through
these channels, whereas Cl
may be released through other
channels or carriers such as the KCl transporters (for review see Ref.
5).
The contribution of channel-mediated vs. carrier-mediated efflux of
Cl from cells depends not only on the complement of
channels and transporters present but also on the distribution of
Cl
across the cell membrane and the equilibrium potential
of Cl
relative to the resting potential of the cell. In
cultured astrocytes, evidence clearly points to an active accumulation
of Cl
and a Cl
equilibrium potential
positive to that of the K+-dominated resting potential (for
review see Ref. 33). Therefore, activation of
Cl
channels alone could effectively result in a net
efflux of Cl
. Indeed, cultured astrocytes exhibit a
depolarization (15, 17) during volume regulation that is
consistent with activation of channels in which the permeant species
exhibits an equilibrium potential positive to the resting potential of
the cell.
Similarly, at least two studies have suggested an active accumulation
of Cl in astrocytes in situ (21, 34)
although a study by Ballanyi and colleagues (1) instead
suggested a passive distribution of Cl
in glial cells in
situ. In contrast to active accumulation, such a passive distribution
of Cl
would result in an equilibrium potential of
Cl
that is similar to that of the resting potential of
the cell. Therefore, a net efflux of Cl
through channels
would be limited by a requirement for channel activation combined with
cell hyperpolarization. In this case, a carrier-mediated component such
as KCl cotransport that is coupled to an outward driving force for
K+ might be required for effective Cl
efflux.
Pasantes-Morales and colleagues (27, 30) provided
additional evidence for KCl efflux through channels in cultured
cerebellar astrocytes. In their studies, volume regulation of
cerebellar astrocytes was inhibited by the K+ channel
blocker quinidine and the Cl channel blocker
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) but was not
affected by the KCl transport blocker bumetanide and only weakly
inhibited by high concentrations of the KCl transport blocker
furosemide. Kimelberg and Frangakis (14) similarly showed that volume regulation of cultured cortical astrocytes was not significantly affected by furosemide.
In this study, we examined volume regulation of astrocytes isolated
from different brain regions, including cortex, hippocampus, and
cerebellum. We found that all of these astrocytes, irrespective of
brain region, showed a regulatory volume decrease in response to
hypotonic challenge that depended on Cl efflux through
ion channels rather than transporters.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell culture. Primary astrocyte cultures were established from Sprague-Dawley rats at postnatal days 0-2 by modification of the technique described by McCarthy and deVellis (22). The protocol was reviewed and approved by the Institutional Animal Care and Use Committee. The pups were placed on ice and decapitated. The brain tissue was dissected in ice-cold Dulbecco's modified Eagle's medium (DMEM; Life Technologies, Grand Island, NY). The meninges and associated blood vessels were removed, and the cortex or region of interest was separated from surrounding regions. We then microscopically reexamined the tissue and removed any remaining blood vessels until the tissue was essentially vessel free. The tissue pieces were further minced, washed with DMEM, and incubated in enzyme solution (warmed to 37°C and bubbled with 100% O2 for 10 min before) for 20 min at 37°C. The enzyme solution consisted of DMEM supplemented with 20 U/ml papain, 1 mmol L-cysteine, 0.5 mmol EDTA, and 706 U/ml deoxyribonuclease (Worthington, Freehold, NJ). The cells were pelleted by centrifugation for 2 min. The supernatant was aspirated, and the remaining pellet was dissociated by trituration (10-15×) with a fire-polished Pasteur pipette into astrocyte medium supplemented with 10 U/ml penicillin, 10 µg/ml streptomycin, and 0.025 µg/ml amphotericin B (Life Technologies). Astrocyte medium consisted of DMEM and 7% heat-inactivated fetal calf serum (HyClone, Logan, UT). The cells were plated onto tissue culture-treated dishes (Fisher) and then kept at 37°C in a 95% O2-5% CO2 atmosphere. The medium was replaced every 3 days.
Cell volume measurements. Cell volume measurements were performed by electronic sizing with a Coulter counter Multisizer 3 (Beckman-Coulter, Miami, FL). Cells were washed in phosphate-buffered saline (PBS) and lifted by 3- to 5-min incubation with 0.05% trypsin and 0.53 mM EDTA (Life Technologies). Trypsin was inactivated by addition of an equal volume of astrocyte medium, and cells were pelleted by brief centrifugation. Cells were resuspended in bath solution of interest and passed through a 40-µm nylon cell strainer (Fisher). A single-cell suspension was verified by microscopic visualization of a sample aliquot. Cells were equilibrated for ~10 min before first reading. Cell volume measurements were obtained every minute, and each measurement was an average of 15,000 cells. Hypotonic challenge was applied after baseline readings.
Solutions for volume regulation experiments. The control NaCl bath solution for cell volume measurements was as follows (in mM): 140 NaCl, 2.5 KCl, 10.5 glucose, 25 HEPES, 1 CaCl2, and 1.2 MgCl2. Anion substitutions were made by replacement of 140 mM NaCl with the appropriate Na salt. Zero-calcium solution was made by omitting CaCl2 and by adding 500 µM EGTA. pH was adjusted to 7.4 with NaOH. Solution osmolarities were confirmed with a vapor pressure osmometer (Wescor 5500; Wescor, Logan, UT). The osmolarities of our isotonic solutions were 310 ± 5 mosM. Drugs were added directly to the bath solutions from stock solutions. Stock solutions of 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), niflumic acid, and bumetanide were dissolved at 1,000× final concentration in DMSO, CdCl2 was dissolved at 1,000× final concentration in double-distilled H2O, furosemide was dissolved at 500× final concentration in DMSO, and DIDS was dissolved at 250× final concentration in 0.1 M KHCO3. DMSO and KHCO3 did not affect volume regulation at their final concentrations. Solutions were made hyposmotic by addition of water.
Media for overnight anion substitution were prepared identically to minimum essential medium (MEM; no. 51200, Life Technologies) except for the equimolar substitution of NaCl with the appropriate Na salt. The solutions consisted of (in mM) 116 Na salt, 5.4 KCl, 26 NaHCO3, 1 NaH2PO4, 0.8 MgSO4, 1.8 CaCl2, and 25.5 glucose with 10 mg/l phenol red, 1× MEM amino acids (Mediatech, Herndon, VA), and 1× MEM vitamin solution (Mediatech). During overnight incubation in these media, cells were kept at 37°C in a 95% O2-5% CO2 atmosphere. Volume regulation after overnight incubation in MEM-like solution with NaCl was similar to that of normal DMEM media (data not shown).Data analysis for volume regulation experiments.
Coulter counter data were collected with Multisizer 3 software, and
size listings were exported to Excel. Time points were rounded to whole
minutes, and mean cell volumes were normalized to baseline value. All
data were plotted in Origin 6.0 (MicroCal, Northampton, MA) as
means ± SE with the number of experiments performed
(n). Significance (P) was determined by
Student's t-test of relative volumes at 30 min after
swelling. Percent regulation was determined as [1 (relative
volume at 30 min/peak relative volume)].
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Astrocytes exhibit volume regulation in response to hypotonic
challenge.
The first step in this study was to establish a consistent and
reproducible cell swelling and regulation of cell volume in primary rat
cortical astrocytes upon hypotonic challenge. Therefore, cells were
suspended in a given volume of NaCl bath solution (see MATERIALS
AND METHODS) and exposed to a 25%, 50%, or 70% reduction in
osmolarity. Mean cell volume of 15,000 cells was monitored once every
minute by electronic sizing with a Coulter counter (see MATERIALS
AND METHODS). Figure 1A
shows the mean normalized peak swelling response of astrocytes to these
degrees of hypotonic challenge. On average, cells swelled to 122 ± 4%, 154 ± 12%, and 180 ± 10% of their original volume
in response to a 25%, 50%, and 70% reduction in osmolarity,
respectively. Addition of the same volume of isosmotic NaCl bath or
sucrose solution produced no swelling (Fig. 1B). It should
be noted that actual cell swelling was less than theoretically
predicted for a given reduction in osmolarity, which could be
attributed to nonosmotically active space within the cells. For
astrocytes, Olson and Holtzman (24) approximated the
nonsolvent volume of astrocytes to be 30%.
|
Volume regulation of astrocytes requires anion flux.
To determine the contribution of anion flux to volume regulation, we
performed anion substitution experiments. We incubated cells overnight
in media in which NaCl was replaced with equimolar Na salts of various
monovalent anions (see MATERIALS AND METHODS). Overnight
incubation allowed for maximal exchange of intracellular Cl with the test anion. It has been shown that with only
20-min incubation in gluconate
- or
NO
content decreases by 80% and 95%, respectively in
cerebellar astrocytes (30). We did not measure the
intracellular Cl
content after overnight substitution in
cortical astrocytes. However, we did observe that the magnitude of
volume regulation after overnight substitution differed from that after
acute substitution for selected anions. An example of this is shown in
Figs. 2B and 3A for
isethionate
substitution. The enhanced inhibition of
volume regulation after overnight substitution of
isethionate
was consistent with successful intracellular
substitution of Cl
with a less permeant anion. An
exception to this was I
substitution, for which
inhibition of regulation was observed after both acute and overnight
exposure as explained below and in Acute I
substitution inhibits volume regulation of astrocytes.
|
|
Acute I substitution inhibits
volume regulation of astrocytes.
The Cl
> I
permeability sequence in
volume regulation was surprising because many Cl
channels
show a lyotropic permeability sequence in which I
is more
permeable than Cl
(8). Therefore, this
observation was further explored. Permeability ratios of
I
to Cl
can be confounded by a blocking
action of I
(8), and both intracellular and
extracellular I
can reduce currents through some
Cl
channels (6).
Cl channel blockers, but not
Cl
transport blockers, inhibit volume
regulation of astrocytes.
To examine the relative contribution of Cl
transporters
vs. channels to volume regulation, the effects of several
Cl
transport and channel blockers were investigated.
First, drugs known to block the Na-K-2Cl and KCl families of
transporters were tested. Either 200 µM furosemide or 50 µM
bumetanide was applied to the suspension of astrocytes before swelling.
Volume regulation was similar to control in the presence of either drug
(Fig. 4A; n = 4 for each
drug), suggesting that ion flux by these
transporters is not necessary during the acute volume regulatory phase
of cultured cortical astrocytes.
|
Removal of extracellular Ca2+ does
not mimic effects of cadmium.
Cadmium is also a potent blocker of voltage-gated Ca2+
channels that are present in glial cells (20). Activation
of Ca2+ channels causes a rise in intracellular
Ca2+ that could act as a second messenger to influence
volume regulation via downstream targets. These targets could include
but are not limited to inhibition of Ca2+-activated
Cl channels. For example, inhibition of
Ca2+-activated K+ channels could also influence
volume regulation. Therefore, we wanted to test whether the inhibition
of volume regulation by Cd2+ could be mediated through
Ca2+ channels rather than direct inhibition of
Cl
channels.
|
Different brain regions show similar volume regulation.
The above data suggest a major role for Cl channels in
volume regulation of rat cortical astrocytes. We next tested whether this is a phenomenon that is specific for cortical astrocytes or
whether similar Cl
channels are also involved in volume
regulation of astrocytes from other brain regions. Volume regulation of
cerebellar, hippocampal, and cortical astrocytes was compared. As shown
in Fig. 6A (n = 4 for cerebellum, n = 4 for hippocampus,
n = 9 for cortex), volume regulation was similar in
astrocytes from all three brain regions. Also, volume regulation of
each region was sensitive to I
and NPPB
(n = 3 for cerebellum, Fig. 6B; hippocampus, not
shown), suggesting that Cl
channels are important in
volume regulation of astrocytes isolated from different regions of the
brain.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
This study addressed the contribution of Cl channels
to volume regulation of rat cortical astrocytes, and our data suggested that under our experimental conditions, Cl
channel-mediated efflux of anions is essential for volume regulation. Ion replacement studies suggest that volume regulation is supported by
some anions that have previously been shown to permeate
Cl
channels but not by anions with little or no
permeability. Moreover, from this data, we constructed a relative
permeability sequence for anions through the pathway mediating volume
regulation. Both isethionate
and gluconate
inhibited volume regulation, in line with their typical poor permeability through Cl
channels. This clearly implied a
dependence of volume regulation on anion flux. These data also
suggested that the pathway involved was not exclusively dependent on
Cl
, as expected for a transporter-mediated pathway, but
rather allowed a number of different anions to permeate, as expected
for a channel-mediated pathway.
Furthermore, we evaluated the effects of Cl channel and
transporter blockers on volume regulation. Neither bumetanide nor furosemide, selective blockers of Cl
transporters,
affected volume regulation, whereas typical Cl
channel
blockers inhibited volume regulation. Therefore, we propose that volume
regulation of cultured astrocytes is dependent on an efflux of anions
through Cl
channels and that to induce volume change
these channels likely cooperate with separate cation and water channels.
Previous studies have shown that cortical astrocytes also release
significant amounts of their intracellular osmolyte pool in response to
hypotonic challenge (26). Necessarily, this efflux of
osmolytes along with water also opposes increases in cell volume and is
likely cooperative with KCl efflux. On the basis of their work on C6
glioma cells, Jackson and colleagues (9, 10) proposed that
in response to cell swelling, Cl and osmolytes permeate a
common pathway that they termed volume-sensitive organic osmolyte-anion
channel (VSOAC). Similarly, Roy (28) showed that amino
acids could diffuse through anion channels in U-138 glioma cells. Our
experiments did not address whether the Cl
channels that
contribute to volume regulation of astrocytes also flux osmolytes.
However, overnight substitution of Cl
with
methanesulfonate
, which is structurally related to
taurine, supported volume regulation similarly to control (Fig.
2B). The fact that methanesulfonate
but not
other large anions such as isethionate
and
gluconate
supported volume regulation was a bit
surprising. However, it is possible that the Cl
channels
involved in volume regulation show a higher than expected permeability
to taurine and its analogs. Therefore, the Cl
channels
involved in volume regulation of cortical astrocytes may regulate cell
volume through both KCl and osmolyte efflux.
The molecular identity of the Cl channels responsible for
volume regulation is not known. Our pharmacology experiments did suggest that more than one channel population might be involved: one
that is inhibited by NPPB and partially by niflumic acid and DIDS and
one that is inhibited by Cd2+. Therefore, the biophysical
properties that we observed, such as anion permeabilities, may have
been derived from a combination of more than one channel. This may
explain why our permeabilities did not follow either the typical
lyotropic sequence described for many anion channels including typical
swelling-activated Cl
channels nor the alternative
sequence described for the voltage-gated Cl
channel
ClC-1, in which larger anions have reduced permeability (8).
Most interesting was that either overnight or acute substitution of
I resulted in complete inhibition of volume regulation.
This may suggest that I
sensitivity is a property shared
among the different channels involved. Such sensitivity has been
described for several anion channels including ClC-1 and cystic
fibrosis transmembrane conductance regulator (CFTR) (6, 19,
29). More experiments are needed to characterize and identify
the channel(s) involved, and this will be addressed in future
electrophysiological and molecular experiments.
![]() |
ACKNOWLEDGEMENTS |
---|
This work was supported by National Institute of Neurological Disorders and Stroke Grant RO1-NS-36692 to H. Sontheimer. K. A. Parkerson was supported by the National Institutes of Health Medical Scientist Training Program.
![]() |
FOOTNOTES |
---|
Address for reprint requests and other correspondence: H. Sontheimer, 1719 6th Ave. South, CIRC 545, Birmingham, AL 35294 (E-mail: sontheimer{at}uab.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.
First published February 26, 2003;10.1152/ajpcell.00603.2002
Received 26 December 2002; accepted in final form 17 February 2003.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Ballanyi, K,
Grafe P,
and
Ten Bruggencate G.
Ion activities and potassium uptake mechanisms of glial cells in guinea-pig olfactory cortex slices.
J Physiol
382:
159-174,
1987[Abstract].
2.
Bond, TD,
Ambikapathy S,
Mohammad S,
and
Valverde MA.
Osmosensitive Cl currents and their relevance to regulatory volume decrease in human intestinal t84 cells: outwardly vs. inwardly rectifying currents.
J Physiol
511:
45-54,
1998
3.
Duan, D,
Ye L,
Britton F,
Horowitz B,
and
Hume JR.
A novel anionic inward rectifier in native cardiac myocytes.
Circ Res
86:
E63-E71,
2000[ISI][Medline].
4.
Enz, R,
Ross BJ,
and
Cutting GR.
Expression of the voltage-gated chloride channel ClC-2 in rod bipolar cells of the rat retina.
J Neurosci
19:
9841-9847,
1999
5.
Eveloff, JL,
and
Warnock DG.
Activation of ion transport systems during cell volume regulation.
Am J Physiol Renal Fluid Electrolyte Physiol
252:
F1-F10,
1987
6.
Fahlke, C,
Durr C,
and
George AL, Jr.
Mechanism of ion permeation in skeletal muscle chloride channels.
J Gen Physiol
110:
551-564,
1997
7.
Ferroni, S,
Marchini C,
Nobile M,
and
Rapisarda C.
Characterization of an inwardly rectifying chloride conductance expressed by cultured rat cortical astrocytes.
Glia
21:
217-227,
1997[ISI][Medline].
8.
Halm, DR.
Identifying swelling-activated channels from ion selectivity patterns.
J Gen Physiol
112:
369-371,
1998
9.
Jackson, PS,
Morrison R,
and
Strange K.
The volume-sensitive organic osmolyte-anion channel VSOAC is regulated by nonhydrolytic ATP binding.
Am J Physiol Cell Physiol
267:
C1203-C1209,
1994
10.
Jackson, PS,
and
Strange K.
Volume-sensitive anion channels mediate swelling-activated inositol and taurine efflux.
Am J Physiol Cell Physiol
265:
C1489-C1500,
1993
11.
Kajita, H,
Omori K,
and
Matsuda H.
The chloride channel ClC-2 contributes to the inwardly rectifying Cl conductance in cultured porcine choroid plexus epithelial cells.
J Physiol
523:
313-324,
2000
12.
Kimelberg, HK.
Swelling and volume control in brain astroglial cells.
In: Advances in Comparative and Environmental Physiology, edited by Gilles R.. Berlin: Springer, 1991.
13.
Kimelberg, HK.
Cell volume in the CNS: regulation and implication for nervous system function and pathology.
Neuroscientist
6:
13-24,
2000.
14.
Kimelberg, HK,
and
Frangakis MV.
Furosemide- and bumetanide-sensitive ion transport and volume control in primary astrocyte cultures from rat brain.
Brain Res
361:
125-134,
1985[ISI][Medline].
15.
Kimelberg, HK,
and
Kettenmann H.
Swelling-induced changes in electrophysiological properties of cultured astrocytes and oligodendrocytes. I. Effects on membrane potentials, input impedance and cell-cell coupling.
Brain Res
529:
255-261,
1990[ISI][Medline].
16.
Kimelberg, HK,
and
Mongin AA.
Swelling-activated release of excitatory amino acids in the brain: relevance for pathophysiology.
Contrib Nephrol
123:
240-257,
1998[ISI][Medline].
17.
Kimelberg, HK,
and
O'Connor E.
Swelling of astrocytes causes membrane potential depolarization.
Glia
1:
219-224,
1988[ISI][Medline].
18.
Lang, F,
Busch GL,
Ritter M,
Volkl H,
Waldegger S,
Gulbins E,
and
Haussinger D.
Functional significance of cell volume regulatory mechanisms.
Physiol Rev
78:
247-306,
1998
19.
Linsdell, P.
Relationship between anion binding and anion permeability revealed by mutagenesis within the cystic fibrosis transmembrane conductance regulator chloride channel pore.
J Physiol
531:
51-66,
2001
20.
MacVicar, BA.
Voltage-dependent calcium channels in glial cells.
Science
226:
1345-1347,
1984[ISI][Medline].
21.
MacVicar, BA,
Tse FWY,
Crichton SA,
and
Kettenmann H.
GABA-activated Cl channels in astrocytes of hippocampal slices.
J Neurosci
9:
3577-3583,
1989[Abstract].
22.
McCarthy, KD,
and
deVellis J.
Preparation of separate astroglial and oligodendroglial cell cultures from rat cerebral tissue.
J Physiol
85:
890-902,
1980.
23.
O'Connor, ER,
and
Kimelberg HK.
Role of calcium in astrocyte volume regulation and in the release of ions and amino acids.
J Neurosci
13:
2638-2650,
1993[Abstract].
24.
Olson, J,
and
Holtzman D.
Respiration and cell volume of primary cultured cerebral astrocytes in media of various osmolarities.
Brain Res
246:
273-279,
1982[ISI][Medline].
25.
Olson, JE,
Sankar R,
Holtzman D,
James A,
and
Fleischhacker D.
Energy-dependent volume regulation in primary cultured cerebral astrocytes.
J Cell Physiol
128:
209-215,
1986[ISI][Medline].
26.
Pasantes-Morales, H,
Alavez S,
Sanchez OR,
and
Moran J.
Contribution of organic and inorganic osmolytes to volume regulation in rat brain cells in culture.
Neurochem Res
18:
445-452,
1993[ISI][Medline].
27.
Pasantes-Morales, H,
Murray RA,
Lilja L,
and
Moran J.
Regulatory volume decrease in cultured astrocytes. I. potassium- and chloride-activated permeability.
Am J Physiol Cell Physiol
266:
C165-C171,
1994
28.
Roy, G.
Amino acid current through anion channels in cultured human glial cells.
J Membr Biol
147:
35-44,
1995[ISI][Medline].
29.
Rychkov, GY,
Pusch M,
Roberts ML,
Jentsch TJ,
and
Bretag AH.
Permeation and block of the skeletal muscle chloride channel, ClC-1, by foreign anions.
J Gen Physiol
111:
653-665,
1998
30.
Sanchez-Olea, R,
Moran J,
Martinez A,
and
Pasantes-Morales H.
Volume-activated Rb+ transport in astrocytes in culture.
Am J Physiol Cell Physiol
264:
C836-C842,
1993
31.
Schmidt-Nielsen, B.
Comparative physiology of cellular ion and volume regulation.
J Exp Zool
194:
207-220,
1975[ISI][Medline].
32.
Waldegger, S,
Steuer S,
Risler T,
Heidland A,
Capasso G,
Massry S,
and
Lang F.
Mechanisms and clinical significance of cell volume regulation.
Nephrol Dial Transplant
13:
867-874,
1998[Abstract].
33.
Walz, W.
Chloride/anion channels in glial cell membranes.
Glia
40:
1-10,
2002[ISI][Medline].
34.
Walz, W,
and
Wuttke WA.
Independent mechanisms of potassium clearance by astrocytes in gliotic tissue.
J Neurosci Res
56:
595-603,
1999[ISI][Medline].