Two types of calcium channels in bullfrog saccular hair cells

Su, Zhixun; Jiang, S; Gu, Rui; Wei, Yang

doi:10.1016/0378-5955(95)00079-j

Cited by 45 publications

(36 citation statements)

References 27 publications

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“…Several lines of evidence indicate that multiple types of Ca 2+ currents mediate depolarization-induced Ca 2+ influx across the membrane of inner ear hair cells in both mammalian and non-mammalian vertebrates [13,17,29,34,40]. The present study provides new evidence about the nature and the expression of DHP-sensitive and -insensitive Ca 2+ currents in hair cells of the frog crista ampullaris.…”

Section: Discussionmentioning

confidence: 70%

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

Russo

Lelli

Gioglio

et al. 2003

Pflugers Arch - Eur J Physiol

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Ca(2+) currents in hair cells of the frog crista ampullaris were studied using the whole-cell patch-clamp technique. Currents were recorded in situ from hair cells in peripheral, intermediate and central regions of the sensory epithelium. Two types of Ca(2+) currents were found: a partially inactivating current that was expressed by nearly all central cells and by about 65% of intermediate and peripheral cells, and a sustained current expressed by the remaining cell population. The mean Ca(2+) current amplitude was larger in intermediate cells than in central or peripheral cells. The two types of Ca(2+) currents were composed of two components: a large, nifedipine-sensitive (NS) current and a small, nifedipine-insensitive (NI) current. The latter was resistant to SNX-482, omega-conotoxin MVIIC and omega-agatoxin IVA and to omega-conotoxin GVIA, antagonists of R, P/Q and N-type Ca(2+) channels. The amplitude of NS and NI currents varied among peripheral cells, where the current density gradually increased from the beginning of the region toward its end. No significant variation of Ca(2+) current density was detected in hair cells of either intermediate or central regions. These results demonstrate the presence of regional and intraregional variations in the expression of L and non-L Ca(2+) channels in the frog crista ampullaris. Finally, immunocytochemical investigations revealed the presence of Ca(2+) channel subunits of the alpha(1D) type and the unexpected expression of alpha(1B)-subunits.

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Section: Discussionmentioning

confidence: 70%

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

Russo

Lelli

Gioglio

et al. 2003

Pflugers Arch - Eur J Physiol

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“…For example, an mRNA encoding a non-L-type ␣ 1 subunit has been found in the sensory epithelium of the rainbow trout's sacculus. ‡ Moreover, low-conductance channels have been detected in single-channel recordings from hair cells of the chicken's cochlea (45), and putative N-type channels have been described in hair cells of the frog's sacculus (46). In hair cells of the chicken's cochlea, however, at least 95% of the Ca 2ϩ conductance is sensitive to dihydropyridines and can be described by a single activation process (9).…”

Section: Discussionmentioning

confidence: 99%

Predominance of the α _1D subunit in L-type voltage-gated Ca ²⁺ channels of hair cells in the chicken’s cochlea

Kollmar

Montgomery

Fak

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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The voltage-gated Ca 2؉ channels that effect tonic release of neurotransmitter from hair cells have unusual pharmacological properties: unlike most presynaptic Ca 2؉ channels, they are sensitive to dihydropyridines and therefore are L-type. To characterize these Ca 2؉ channels, we investigated the expression of L-type ␣ 1 subunits in hair cells of the chicken's cochlea. In PCRs with five different pairs of degenerate primers, we always obtained ␣ 1D products, but only once an ␣ 1C product and never an ␣ 1S product. A full-length ␣ 1D mRNA sequence was assembled from overlapping PCR products; the predicted amino acid sequence of the ␣ 1D subunit was about 90% identical to those of the mammalian ␣ 1D subunits. In situ hybridization confirmed that the ␣ 1D mRNA is present in hair cells. By using a quantitative PCR assay, we determined that the ␣ 1D mRNA is 100-500 times more abundant than the ␣ 1C mRNA. We conclude that most, if not all, voltage-gated Ca 2؉ channels in hair cells contain an ␣ 1D subunit. Furthermore, we propose that the ␣ 1D subunit plays a hitherto undocumented role at tonic synapses. At most synapses, transmitter release depends on N-type or P-type Ca 2ϩ channels, which are blocked by -conotoxin GIVA and -agatoxin IVA, respectively (reviewed in ref. 5). In hair cells, however, the Ca 2ϩ channels have different pharmacological properties: they are sensitive to dihydropyridines and therefore are L-type channels (6-9). In only a few other cell types, such as cultured sensory neurons (10) and retinal bipolar cells (11), have L-type channels been shown to effect neurotransmitter release.The drug sensitivity and permeability of a voltage-gated Ca 2ϩ channel depend on its type of ␣ 1 subunit (reviewed in ref.12). The pore-forming ␣ 1 protein is 160-240 kDa in size, with a cytoplasmic amino terminus, four homologous repeats (I-IV) of six transmembrane segments (S1-S6) each, and a cytoplasmic carboxyl terminus. L-type channels contain the product of the ␣ 1C (cardiac), the ␣ 1D (neuroendocrine), or the ␣ 1S (skeletal muscle) gene. To characterize the unusual L-type Ca 2ϩ channels that control synaptic transmission, we sought to determine which of these three ␣ 1 genes are expressed in hair cells of the chicken's cochlea. MATERIALS AND METHODSHistology. White Leghorn chickens (Gallus gallus) were asphyxiated with CO 2 and decapitated. The temporal bones with intact cochleae were excised and fixed overnight at 4°C with 0.75% (wt͞vol) paraformaldehyde and 2.5% (vol͞vol) glutaraldehyde in a buffer solution containing 70 mM sodium phosphate (pH 7.4), 75 mM sucrose, and 0.9 mM CaCl 2 . After two rinses in the buffer solution, the cochleae were carefully dissected from the bone, fixed with 1% (wt͞vol) OsO 4 in buffer solution, dehydrated successively with ethanol and propylene oxide, and embedded in epoxy resin consisting of EMbed 812, Araldite 6005, dodecenyl succinic anhydride, and 2,4,6-tris(dimethylaminomethyl)phenol (25:20:60:1 by volume; Electron Microscopy Sciences, Fort Washington, PA). Semithin ...

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“…Molecular biological studies have demonstrated the existence of several VGCC subunits in the auditory and vestibular organs (Beisel et al 1998;Fuchs 1996;Green et al 1996;Kollmar et al 1997a, b;Lopez et al 1999;Platzer et al 2000;Su et al 1995;Zidanic and Fuchs 1995). A critical role of the a1D VGCC subunit in auditory function has been demonstrated, in that a1D-deficient mice are deaf (Engel et al 2002;Platzer et al 2000).…”

Section: Introductionmentioning

confidence: 95%

Immunolocalization of voltage-gated calcium channel ?1�subunits in the chinchilla cochlea

López

Ishiyama

Acuña

et al. 2003

Cell and Tissue Research

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The immunohistochemical localization of alpha1A, alpha1B, alpha1C, alpha1D, and alpha1E voltage-gated calcium channel subunits was investigated in the chinchilla organ of Corti and spiral ganglia with the use of specific antipeptide antibodies. The inner and outer hair cells were immunoreactive for alpha1A and alpha1D subunit antibodies. Alpha1C immunoreactivity localized to the nerve terminals innervating inner hair cells and the basal pole of the outer hair cell. There was only non-specific staining to alpha1B and alpha1E. Supporting cells were non-immunoreactive. Spiral ganglia neurons were alpha1B, alpha1C, and alpha1D immunoreactive. A few spiral ganglia neurons were alpha1E immunoreactive. The importance of alpha1D, the pore-forming subunit of the L-type channel, in outer and inner hair cell function has been clearly demonstrated in electrophysiological, molecular biological, and knockout models. The presence of alpha1A, the pore-forming subunit of the P/Q type channels, has not previously been demonstrated in inner and outer hair cells, and its function in the cochlear hair cell is unknown.

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Two types of calcium channels in bullfrog saccular hair cells

Cited by 45 publications

References 27 publications

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

Predominance of the α _1D subunit in L-type voltage-gated Ca ²⁺ channels of hair cells in the chicken’s cochlea

Immunolocalization of voltage-gated calcium channel ?1�subunits in the chinchilla cochlea

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Two types of calcium channels in bullfrog saccular hair cells

Cited by 45 publications

References 27 publications

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

Predominance of the α 1D subunit in L-type voltage-gated Ca 2+ channels of hair cells in the chicken’s cochlea

Immunolocalization of voltage-gated calcium channel ?1�subunits in the chinchilla cochlea

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Predominance of the α _1D subunit in L-type voltage-gated Ca ²⁺ channels of hair cells in the chicken’s cochlea