Expression of an inwardly rectifying K+ channel, Kir4.1, in satellite cells of rat cochlear ganglia

Hiroshi Hibino1,2, Yoshiyuki Horio1, Akikazu Fujita1, Atsushi Inanobe1, Katsumi Doi2, Takahiro Gotow3, Yasuo Uchiyama3, Takeshi Kubo2, and Yoshihisa Kurachi1

Departments of 1 Pharmacology II, 2 Otolaryngology, and 3 Anatomy I, Faculty of Medicine and Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Satellite cells are glial cells wrapped around somata of sensory and autonomic ganglion neurons. Neither their functional roles nor electrical properties have been fully clarified so far. Using immunohistochemistry, we found that inwardly rectifying K+ channel subunit Kir4.1 (also called Kir1.2 or KAB-2) was expressed prominently in the satellite cells of cochlear ganglia. The Kir4.1 immunoreactivity was localized specifically at the myelin sheaths of satellite cells wrapping the somata of the ganglion neurons. Developmental expression of Kir4.1 in satellite cells paralleled development of the action potential in the auditory nerve. These results suggest that this channel in satellite cells may be responsible for the regulation of K+ extruded from the ganglion neurons during excitation.

myelin sheaths; potassium-buffering action; immunohistochemistry; development; audition


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

COCHLEAR GANGLION NEURONS belong to bipolar sensory neurons and are excited at their dendrites by neurotransmitters, such as glutamate, released from the hair cells. These neurons project to the cochlear nucleus and thus transduce the hair cell signal to the central auditory system. The somata of cochlear ganglion neurons are usually surrounded by more than two satellite cells (17, 18), as in the case of other types of sensory and autonomic ganglia. Electron microscopic examination has revealed that cochlear satellite cells wrap the somata of ganglion neurons with multiple layers of myelin sheaths, the structure of which is similar to that of the myelin sheaths of Schwann cells surrounding peripheral nerve fibers (17). Because the Schwann cell myelin sheath acts as an insulator and is indispensable for saltatory conduction of action potential in myelinated axons, the satellite cell sheath may also function as an insulator to prevent electrical interaction between the neurons in a ganglion. In Schwann cells, whereas no ion channels exist in the greater part of the myelin sheath, voltage-dependent K+ (Kv) channels (Kv1.5) (11) and inwardly rectifying K+ (Kir) channels (Kir2.1 and Kir2.3) (12) are localized at the outer surfaces and microvilli, respectively, of the edges of Schwann cells facing the Ranvier node region. It has been suggested that the Kir channels are responsible for the uptake by Schwann cells of K+ extruded from axons at the Ranvier node during electrical excitation and that the Kv channel extrudes K+ to the extracellular solution (11, 12). On the other hand, the cellular electrical properties and functional roles of satellite cells have not been fully clarified so far.

We previously cloned Kir channel Kir4.1 (or Kir1.2 or KAB-2), predominantly expressed in brain glial cells (22). This is the same clone as BIR10 (4). During our previous study of Kir4.1 in the cochlear stria vascularis (8), we also detected the prominent immunoreactivity of Kir4.1 in the satellite cells of cochlear ganglia. Therefore, in this study we examined the subcellular localization and developmental expression of Kir4.1 in cochlear satellite cells. We found that Kir4.1 was specifically localized at the myelin sheath membranes of satellite cells. The developmental expression of Kir4.1 in satellite cells paralleled the formation of an action potential by the auditory nerve. These results suggest that the Kir4.1 channel is involved in the K+-buffering action of satellite cells in cochlear ganglia, a suggestion that may be applicable to other sensory ganglia, such as vestibular, trigeminal, and superior cervical ganglia.


    METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Immunohistochemistry. Affinity-purified anti-Kir4.1 antibody (anti-KAB-2C2), which was raised against the amino acid sequence in the COOH-terminal end of rat Kir4.1 (EKEGSALSVRISNV), was prepared, and immunohistochemistry was performed as described previously (8, 10). Briefly, adult female Sprague-Dawley rats (SLC, Hamamatsu, Japan; 130-170 g) were anesthetized intramuscularly with pentobarbital sodium (Nembutal; Abbott, Chicago, IL) and fixed with 4% paraformaldehyde-0.1 M sodium phosphate, pH 7.4. The ear capsules were exposed and broken out, and then cochleas were isolated. The cochleas were decalcified in EDTA solution (9% EDTA · 2Na, 10% EDTA · 4Na, pH 7.4) at 4°C for 5 days. Cochlear cryosections (10 µm thick) were incubated with anti-KAB-2C2 (0.08 µg/ml) and treated with an ABC kit (Vector Laboratories, Burlingame, CA). Nuclei were stained with hematoxylin after immunostaining. Negative-control sections were treated with anti-KAB-2C2 in the presence of an excess amount of the antigen oligopeptide. For double immunostaining, the sections were treated with anti-KAB-2C2 and anti-neurofilament 160 antibody (Boehringer Mannheim Biochemica) or anti-vimentin antibody (Zymed Laboratory, San Francisco, CA) and incubated with FITC-labeled anti-rabbit antibody and Texas red-labeled anti-mouse antibodies. Confocal images were obtained under a laser scanning microscope (MRC-1024; Bio-Rad, Hertfordshire, England) by using its sequential mode (excitation wave: FITC, 488 nm; Texas red, 568 nm).

Immunogold electron microscopy. Immunogold electron microscopic analysis was performed as described previously (7, 14). Briefly, rats were fixed with 0.1% glutaraldehyde and 4% paraformaldehyde in 0.1 M phosphate buffer and postfixed overnight. Small fixed blocks of cochlear modiolus including spiral ganglia and nerve fibers were cryoprotected by immersion in graded concentrations of glycerol (10, 20, and 30%) in phosphate buffer and plunged into liquid propane (-170°C) in a cryofixation unit (KF80; Reichert, Vienna, Austria). The samples were then immersed in 0.5% uranyl acetate dissolved in anhydrous methanol (-90°C) in a cryosubstitution unit (AFS; Reichert). The temperature was raised in steps of 4°C/h to -45°C. Samples were washed with anhydrous methanol and infiltrated with Lowicryl HM20 resin at -45°C, with a progressive increase in the ratio of resin to methanol. Polymerization was performed with UV light (360 nm) for 48 h. Ultrathin sections were cut with a Reichert ultramicrotome and mounted on nickel grids. The sections were treated with a saturated solution of NaOH in absolute ethanol (1-2 s), rinsed in phosphate buffer, and incubated sequentially in the following solutions at room temperature: 1) 0.1% sodium borohydride and 50 mM glycine in Tris buffer (5 mM) containing 0.01 or 0.1% Triton X-100 and 50 mM NaCl (TBNT; 10 min); 2) 2% human serum albumin in TBNT (10 min); 3) first antibody (anti-KAB-2C2; 30 µg/ml) diluted in the same solution as in 2 (2 h); 4) same solution as in 2 (10 min); and 5) gold-conjugated secondary antibody (10-nm particles) diluted 1:20 in TBNT containing human serum albumin and polyethylene glycol (0.5 mg/ml; 1 h). Finally, the sections were counterstained and examined in an electron microscope.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Expression of Kir4.1 (KAB-2) in satellite cells of spiral ganglia in rat inner ear. We have developed a specific antibody to the COOH terminus of Kir4.1 (anti-KAB-2C2) (7-10). Figure 1A shows an immunohistochemical examination of a sliced section of rat cochlea using anti-KAB-2C2 antibody. Nuclei in this section were stained with hematoxylin. Kir4.1 immunoreactivity was detected in marginal cells of the stria vascularis, Deiters' cells and pillar cells in the organ of Corti, and spiral ganglia, as reported previously (8, 23). Figure 1B depicts the immunostaining of Kir4.1 in spiral ganglia at higher magnification. Strong Kir4.1 immunoreactivity seemed to be localized at the surfaces of satellite cells facing towards somata of ganglion neurons (Fig. 1B and sketch at right). Cochlear ganglion neurons have been classified into type I and type II (20). The somata of the type I neurons, which constitute >90% of the ganglion neurons, are larger than those of type II (Fig. 1B). In rats, both type I and II ganglion neuronal somata are wrapped by satellite cells (17, 18). Kir4.1 immunoreactivity was detected not only in type I but also in type II ganglion neurons (Fig. 1B). These immunoreactivities were specific, because no immunoreactivity was detected when anti-KAB-2C2 antibody that had been preabsorbed with an excess amount of immunizing oligopeptide was used (data not shown). However, at the level of light microscopic examination, it was difficult to resolve whether the immunoreactivity is localized on the membranes of somata of neurons or those of satellite cells or both.


View larger version (62K):
[in this window]
[in a new window]
 
Fig. 1.   Immunohistochemical localization of Kir4.1 in rat cochlea. A: immunohistochemistry of cochlea by using anti-Kir4.1 antibody. Kir4.1 immunoreactivity was localized in spiral ganglia (large arrow), stria vascularis (small arrowheads), and Deiters' and pillar cells in organ of Corti (small arrow). B: high-power magnification of spiral ganglia stained with anti-Kir4.1 antibody. Immunoreactivity was localized at surfaces of satellite cells (SC) facing toward somata of ganglion neurons (GC; boldface line in sketch at right). Type II ganglia (white arrow) also showed immunoreactivity. Scale bars: A, 100 µm; B, 20 µm.

Confocal microscopic analysis of Kir4.1 immunoreactivity. To determine in which cell of the cochlear ganglion Kir4.1 is expressed, we performed double immunostaining of Kir4.1 and either neurofilament (NF), a marker of neurons, or vimentin, an intermediate filament specifically expressed in glial cells (Fig. 2).


View larger version (77K):
[in this window]
[in a new window]
 
Fig. 2.   Double immunostaining of spiral ganglia with anti-Kir4.1 and neurofilament (NF) (top) or vimentin (bottom). Immunoreactivity of Kir4.1 (green) was colocalized with that of vimentin (red at bottom) but not that of NF (red at top). "Transmitted" indicates transparent image. Scale bar: 50 µm.

Figure 2, top, shows the confocal microscopic images of the double immunostaining of Kir4.1 (green) and NF (red) in spiral ganglia. NF immunoreactivity was detected in somata and nerve fibers of ganglion neurons but not in the satellite cells, as reported previously (2, 16). The overlaid image of Kir4.1 and NF immunoreactivities generated no yellow color, indicating that Kir4.1 was not expressed either in the somata or in the nerve fibers of the ganglion neurons.

On the other hand, vimentin immunoreactivity (red) was detected in satellite cells but not in ganglion neurons (Fig. 2, bottom) (1, 24). The overlay of the images of Kir4.1 and vimentin generated prominent yellow signals. These results strongly suggest that Kir4.1 is expressed in satellite cells but not either in the somata or in the nerve fiber of ganglion neurons.

Subcellular localization of Kir4.1 in the satellite cells of cochlear ganglia. The subcellular localization of Kir4.1 was further examined by immunoelectron microscopy of ultrathin sections in cochlear type I spiral ganglia (Fig. 3). The somata of spiral ganglion neurons were surrounded by multiple layers of myelin sheaths of satellite cells (Fig. 3, A and B). The myelin sheaths of satellite cells were looser and thinner than those of Schwann cells, which wrapped axonal fibers of the ganglion neurons (compare the sheaths shown in Fig. 3, A and B, with those in Fig. 3, D and E) (17). Gold particles of Kir4.1 immunoreactivity were detected abundantly on the layers of myelin sheaths of satellite cells (Fig. 3, A and B) but not either on the outermost membranes of satellite myelin sheaths (Fig. 3, A and B) or on the somatic membranes of satellite cells (Fig. 3C), both of which face the connective tissue. Gold particles were also not detected at the somatic membranes of ganglion neurons (Fig. 3, A, A insets, and B). The same results were obtained with type II ganglion neurons (data not shown). On the other hand, no gold particles were detected on the Schwann cell sheaths wrapping the axonal nerve fibers of ganglion neurons (Fig. 3, D and E). Furthermore, we did not detect any gold particles of Kir4.1 immunoreactivity on either the outer surfaces or microvilli (Fig. 3D) of the edges of Schwann cells facing the Ranvier node region, where the Kv channel (Kv1.5) (11) and Kir channel (Kir2.1 and Kir2.3) (12), respectively, are reported to be expressed. These results clearly indicate that Kir4.1 is specifically localized at the myelin sheaths of satellite cells.


View larger version (108K):
[in this window]
[in a new window]
 
Fig. 3.   Immunogold electron microscopic analysis of Kir4.1 immunoreactivity in satellite cells (SC). Electron microscopic images of portions are indicated in schema at top. Positive gold particles were detected only in myelin sheaths (A and B), but not at outermost membranes (A and B; thin arrows) of satellite cells. Somatic membrane of satellite cell (C; arrows), ganglion neuron (GC) (A, A insets, and B; arrowheads), and myelin sheaths of Schwann cells (SwC) surrounding nerve fibers (NF; D and E; *) were free from positive gold particles. Gold particles were also not detected at either outer surfaces (D; arrows) or microvilli (MV; D) of Schwann cells facing Ranvier node region. A, insets: high-magnification view of regions marked with thick arrows. C, star  nucleus of satellite cell. Scale bars: A-E, 150 nm; A, insets, 50 nm.

Developmental expression of Kir4.1 in the satellite cells of cochlear ganglia. In rats just after birth, the function and structure of auditory systems, including the cochlea, are immature and nonfunctional. They are gradually developed and become mature within ~2 wk after birth, when the onset of hearing in rats is known to occur (3). To clarify the relationship between auditory function and Kir4.1 expression in satellite cells, we examined the developmental change of Kir4.1 immunoreactivity in cochlear satellite cells of rats at various postnatal days [postnatal days 1-14 (P1-P14)] (Fig. 4).


View larger version (123K):
[in this window]
[in a new window]
 
Fig. 4.   Developmental studies of expression of Kir4.1 in satellite cells. All sections were stained by the ABC-diaminobenzidine method. Arrowheads, cochlear satellite cells that show Kir4.1 immunoreactivity. A and D, postnatal day 10 (P10); B and E, P12; C and F, P14. Scale bar: 30 µm.

At the first day after birth (P1) and P5, cochlear ganglion cells were small and poorly developed but had already been enveloped by satellite cells (21). No satellite cells expressed Kir4.1 at P1 and P5. At P8, approximately when the myelin sheaths of satellite cells begin to envelop the somata of ganglion neurons (21), weak immunoreactivity of Kir4.1 could be detected in some but not all satellite cells. The Kir4.1 immunoreactivity gradually increased in the following several days [Fig. 4, A and D (P10), and B and E (P12)] and reached the adult level at P14. This pattern of developmental expression of Kir4.1 was the same in all turns of the cochlea (data not shown). The time course of Kir4.1 expression in satellite cells was in parallel with that in marginal cells of the stria vascularis (8) and also with the development of the action potential of the auditory nerve (13). Because the onset of hearing occurs at P14, which is just after the complete maturation of Kir4.1 expression in satellite cells as well as in the stria vascularis, it is possible that Kir4.1 in satellite cells as well as in the stria vascularis may play an important functional role in establishing auditory function.

Immunohistochemistry of Kir4.1 in various types of ganglia and peripheral nerves. Satellite cells are known to sheathe neuronal somata in all sensory and autonomic ganglia (15). To investigate whether the expression of Kir4.1 was specific to the ganglia of the eighth cranial nerve, we examined the distribution of Kir4.1 in other types of ganglia.

Kir4.1 immunoreactivity could be detected in the satellite cells of vestibular ganglia of the inner ear in a pattern similar to that in cochlear ganglia (Fig. 5A). We could also show prominent Kir4.1 immunoreactivity of trigeminal ganglia, another type of sensory ganglion of cranial nerves (Fig. 5B). We could find the expression of Kir4.1 in the satellite cells of superior cervical ganglia, one of the sympathetic ganglia of autonomic neurons (Fig. 5C). The patterns of Kir4.1 immunoreactivity of trigeminal and superior cervical ganglia seemed to be similar to that of auditory ganglia. On the other hand, the satellite cells of either dorsal root ganglia of general somatic sensory neurons or those in Auerbach's plexus of the small intestine, which are parasympathetic neurons, did not express Kir4.1 (Fig. 5, D and E, respectively).


View larger version (116K):
[in this window]
[in a new window]
 
Fig. 5.   Immunohistochemistry of Kir4.1 in various types of ganglia and peripheral nerves. Kir4.1 was expressed in the satellite cells of vestibular ganglia (A), trigeminal ganglia (B), and superior cervical ganglia (C), but not in either dorsal root ganglia (D) or ganglia of Auerbach's plexus in small intestine (E, arrowheads). No immunoreactivity was observed in cauda equina (F) and optic nerves (G). * Crypt of small intestine. Scale bars: A, 50 µm; B, C, and D, 100 µm; E, 30 µm; F and G, 100 µm.

Peripheral nerves are known to be compactly covered by myelin sheaths. The fibers of the cauda equina and optic nerve are wrapped with the myelin sheaths of Schwann cells and oligodendrocytes, respectively. We observed no immunoreactivity of Kir4.1 in the cauda equina (Fig. 5F) and in optic nerves (Fig. 5G).

These results indicate that Kir4.1 is localized in the satellite sheaths of some ganglia but not in the myelin sheaths of peripheral nerves.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The major findings of this study are the following: 1) in cochlear ganglia, Kir4.1 was specifically expressed in myelin sheaths of the satellite cells surrounding neurons; 2) developmental expression of Kir4.1 in satellite cells approximately paralleled the formation of action potential by the auditory nerve; and 3) Kir4.1 was also expressed in the satellite cells of some ganglia, such as vestibular, trigeminal, and superior cervical ganglia.

Putative functions of Kir4.1 in cochlear satellite cells. Although satellite cells surround the somata of ganglion neurons with myelin sheaths, the sheaths, compared with those of Schwann cells surrounding axon fibers, are not as tight and are not devoid of cytosol (Fig. 3 and Ref. 17). They may, therefore, have functions other than just the insulation of individual ganglion neurons from their neighbors and the prevention of electrical interference. Schwann cell membranes are not entirely devoid of ion channels. Kir and Kv channels are localized to the Schwann cell membrane at the node of Ranvier where axonal K+ flows occur, and they may be involved in the absorption of extra-axonal K+ via Kir and the extrusion of K+ via Kv channels into the external space (11, 12). Because the somata of ganglion neurons generate the action potential (5, 6, 19), the extracellular K+ may increase during excitation. Thus the localization of Kir4.1 in the myelin sheaths of satellite cells but not in the external membranes may suggest a role in the buffering of K+ extruded from the ganglion neurons. Further studies are required to determine whether and where Kv or other types of K+ channels might be expressed in satellite cells to complete the picture of K+ cycling from the neuron to the extracellular space.

Developmental expression of Kir4.1 in cochlear satellite cells. Developmental expression of Kir4.1 in satellite cells paralleled the maturation of auditory function. In mice, the action potential of the cochlear nerve was first detected at P9, increased over several days, and reached a plateau at P14 (13), when hearing onset is known to occur (3). This time course of development of action potential formation is in parallel with that of Kir4.1 expression in cochlear ganglia. It could be speculated that Kir4.1 allows ganglion neurons to achieve the mature level of excitation in response to sounds. This was also the case in the stria vascularis (8). The subcellular localization of Kir4.1 shown in this study suggested that this channel may play a role in buffering the K+ extruded from the ganglion neurons and that an increase of extracellular K+ might be a signal for induction of the channel in the satellite cells. The developmental alteration of Kir channels in Schwann cells is clearly different from that of Kir4.1 in cochlear satellite cells. Wilson and Chiu (25) reported the early postnatal change of the somal Kir current in Schwann cells by a patch-clamp technique (25). At 1-2 days after birth, a large and remarkable Kir current was observed on the somata of Schwann cells. Whereas the average number of myelin sheath lamellae of Schwann cells increased from 2 to 8 days after birth, Kir currents decreased by 94% and became concentrated in the regions near the node, where K+ is extruded (25). Therefore, the distribution of Kir2.1 and Kir2.3 in Schwann cells may also be regulated by the excretion of K+ from axons. Further studies are needed to determine how the extracellular K+ concentration regulates the distribution of the Kir channels.

Kir4.1 is expressed in specific types of satellite cells. Kir4.1 was specifically expressed in satellite cells, but not either in Schwann cells of peripheral nerves or oligodendrocytes of the optic nerve (Figs. 3, D and E, and 5, F and G). However, the expression of Kir4.1 was not detected in satellite cells of all types of ganglia (Fig. 5); it was detected in vestibular ganglia that also belong to the eighth cranial nerve, trigeminal ganglia, and superior cervical ganglia of sympathetic ganglia, but no immunoreactivity of Kir4.1 was detected in either dorsal root ganglia of the somatic sensory system or Auerbach's ganglia of parasympathetic ganglia. Because the expression of Kir4.1 in satellite cells seems to be related to the excretion of K+ from neuronal somata, the electrophysiological properties of neurons might be different in these two types of ganglia. It is also possible that other types of Kir channels, which do not exhibit Kir4.1 immunoreactivity, are expressed in those satellite cells. Further studies are also needed to clarify this point.


    ACKNOWLEDGEMENTS

We thank Dr. Ian Findlay (Tours, France) for critical reading of this manuscript, Akie Ito and Mari Imanishi for technical assistance, and Keiko Tsuji for secretarial work.


    FOOTNOTES

This work was supported by grants to Y. Kurachi from the Ministry of Education, Culture, Sports and Science of Japan, from the Research for the Future Program of the Japan Society for the Promotion of Science (96L00302), and from the Human Frontier Science Program (RG0158/1997-B).

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. §1734 solely to indicate this fact.

Address for reprint requests and other correspondence: Y. Kurachi, Department of Pharmacology II, Faculty of Medicine and Graduate School of Medicine, Osaka University, 2-2, Yamada-Oka, Suita, Osaka 565-0871, Japan (E-mail: ykurachi{at}pharma2.med.osaka-u.ac.jp).

Received 9 December 1998; accepted in final form 7 June 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Anniko, M., W. Arnold, T. Stigbrand, and A. Ström. The human spiral ganglion. ORL J. Otorhinolaryngol Relat. Spec. 57: 68-77, 1995[Medline].

2.   Baxter, R., L. H. Bannister, H. C. Dodson, and D. V. Gathercole. Protein gene product 9.5 in the developing cochlea of the rat: cellular distribution and relation to the cochlear cytoskeleton. J. Neurocytol. 22: 14-25, 1993[Medline].

3.   Blatchley, B. J., W. A. Cooper, and J. R. Coleman. Development of auditory brainstem response to tone pip stimuli in the rat. Dev. Brain Res. 32: 75-84, 1987.

4.   Bond, C. T., M. Pessia, X.-M. Xia, A. Lagrutta, M. P. Kavanaugh, and J. P. Adelman. Cloning and expression of a family of inward rectifier potassium channels. Receptors Channels 2: 183-191, 1994[Medline].

5.   Czéh, G., N. Kudo, and M. Kuno. Membrane properties and conduction velocity in sensory neurones following central or peripheral axotomy. J. Physiol. (Lond.) 270: 165-180, 1977[Medline].

6.   Gallego, R., and C. Eyzaguirre. Membrane and action potential characteristics of A and C nodose ganglion cells studied in whole ganglia and in tissue slices. J. Neurophysiol. 41: 1217-1232, 1978[Free Full Text].

7.   Gotow, T., J. Tanaka, and M. Takeda. The organization of neurofilaments accumulated in perikaryon following aluminum administration: relationship between structure and phosphorylation of neurofilaments. Neuroscience 64: 553-569, 1995[Medline].

8.   Hibino, H., Y. Horio, A. Inanobe, K. Doi, M. Ito, M. Yamada, T. Gotow, Y. Uchiyama, M. Kawamura, T. Kubo, and Y. Kurachi. An ATP-dependent inwardly rectifying potassium channel, KAB-2 (Kir4.1), in cochlear stria vascularis of inner ear: its specific subcellular localization and correlation with the formation of endo-cochlear potential. J. Neurosci. 17: 4711-4721, 1997[Abstract/Free Full Text].

9.   Ishii, M., Y. Horio, Y. Tada, H. Hibino, A. Inanobe, M. Ito, M. Yamada, T. Gotow, Y. Uchiyama, and Y. Kurachi. Expression and clustered distribution of an inwardly rectifying potassium channel, KAB-2/Kir4.1, on mammalian retinal Müller cell membrane: their regulation by insulin and laminin signals. J. Neurosci. 17: 7725-7735, 1997[Abstract/Free Full Text].

10.   Ito, M., A. Inanobe, Y. Horio, H. Hibino, S. Isomoto, H. Ito, K. Mori, A. Tonosaki, H. Tomoike, and Y. Kurachi. Immunolocalization of an inwardly rectifying K+ channel, KAB-2 (Kir4.1), in the basolateral membrane of distal renal tubular epithelia. FEBS Lett. 388: 11-15, 1996[Medline].

11.   Mi, H., T. J. Deerinck, M. H. Ellisman, and T. L. Schwarz. Differential distribution of closely related potassium channels in rat Schwann cells. J. Neurosci. 15: 3761-3774, 1995[Abstract].

12.   Mi, H., T. J. Deerinck, M. Jones, M. H. Ellisman, and T. L. Schwarz. Inwardly rectifying K+ channels that may participate in K+ buffering are localized in microvilli of Schwann cells. J. Neurosci. 16: 2421-2429, 1996[Abstract].

13.   Mikaelian, D., and R. J. Ruben. Development of hearing in the normal CBA-J mouse. Acta Otol. Laryngol.. 59: 451-461, 1965.

14.   Nagelhus, E. A., M. L. Veruki, R. Torp, F.-M. Haug, J. H. Laake, S. Nielsen, P. Agre, and O. P. Ottersen. Aquaporin-4 water channel protein in the rat retina and optic nerve: polarized expression in Muller cells and fibrous astrocytes. J. Neurosci. 18: 2506-2519, 1998[Abstract/Free Full Text].

15.   Pannese, E. The satellite cells of the sensory ganglia. Adv. Anat. Embryol. Cell Biol. 65: 1-111, 1981[Medline].

16.   Romand, R., H. Sobkowicz, M. Emmerling, D. Whitlon, and D. Dahl. Patterns of neurofilament stain in the spiral ganglion of the developing and adult mouse. Hear. Res. 49: 119-126, 1990[Medline].

17.   Rosenbluth, J. The fine structure of acoustic ganglia in the rat. J. Cell Biol. 12: 329-359, 1962[Abstract/Free Full Text].

18.   Ryan, A. F., and I. R. Schwartz. Preferential amino acid uptake identifies Type II spiral ganglion neurons in the gerbil. Hear. Res. 9: 173-184, 1983[Medline].

19.   Santos-Sacchi, J. Voltage-dependent ionic conductances of type I spiral ganglion cells from the guinea pig inner ear. J. Neurosci. 13: 3599-3611, 1993[Abstract].

20.   Schuknecht, H. F. Anatomy. In: Pathology of the Ear, edited by H. F. Schuknecht. Malvern, PA: Lea & Febiger, 1993, p. 31-75.

21.   Sobkowicz, H. M. The development of innervation in the organ of Corti. In: Development of Auditory and Vestibular Systems 2, edited by R. Romand. Amsterdam: Elsevier, 1992, p. 59-100.

22.   Takumi, T., T. Ishii, Y. Horio, K.-I. Morishige, N. Takahashi, M. Yamada, T. Yamashita, H. Kiyama, K. Sohmiya, S. Nakanishi, and Y. Kurachi. A novel ATP-dependent inward rectifier potassium channel expressed predominantly in glial cells. J. Biol. Chem. 270: 16339-16349, 1995[Abstract/Free Full Text].

23.  Takumi, Y., S. Matsubara, S. Usami, H. Shinkawa, A. Fujita, Y. Horio, A. Inanobe, Y. Kurachi, S. Nielsen, E. A. Nagelhus, and O. P. Ottersen. Differential localization of Kir4.1 and AQP4 in supporting cells: a high resolution immunogold study in the rat organ of Corti (Abstract). Proc. Annu. Meet. Association for Research in Otolaryngology 1999 (http://www.aro.org/archives/1999/327.html).

24.   Vega, J. A., C. Rodriguez, M. Medina, M. E. del Valle-Soto, and L. C. Hernandez. Expression of cytoskeletal proteins in glial cells of dorsal root ganglia. Cell. Mol. Biol. 35: 635-641, 1989[Medline].

25.   Wilson, G. F., and S. Y. Chiu. Potassium channel regulation in Schwann cells during early developmental myelinogenesis. J. Neurosci. 10: 1615-1625, 1990[Abstract].


Am J Physiol Cell Physiol 277(4):C638-C644
0002-9513/99 $5.00 Copyright © 1999 the American Physiological Society