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Predominance of the alpha1D subunit in L-type voltage-gated Ca2+ channels of hair cells in the chicken's cochlea.

ABSTRACT: The voltage-gated Ca2+ channels that effect tonic release of neurotransmitter from hair cells have unusual pharmacological properties: unlike most presynaptic Ca2+ channels, they are sensitive to dihydropyridines and therefore are L-type. To characterize these Ca2+ channels, we investigated the expression of L-type alpha1 subunits in hair cells of the chicken's cochlea. In PCRs with five different pairs of degenerate primers, we always obtained alpha1D products, but only once an alpha1C product and never an alpha1S product. A full-length alpha1D mRNA sequence was assembled from overlapping PCR products; the predicted amino acid sequence of the alpha1D subunit was about 90% identical to those of the mammalian alpha1D subunits. In situ hybridization confirmed that the alpha1D mRNA is present in hair cells. By using a quantitative PCR assay, we determined that the alpha1D mRNA is 100-500 times more abundant than the alpha1C mRNA. We conclude that most, if not all, voltage-gated Ca2+ channels in hair cells contain an alpha1D subunit. Furthermore, we propose that the alpha1D subunit plays a hitherto undocumented role at tonic synapses.

SUBMITTER: Kollmar R

PROVIDER: S-EPMC25132 | biostudies-literature | 1997 Dec

REPOSITORIES: biostudies-literature

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Predominance of the alpha1D subunit in L-type voltage-gated Ca2+ channels of hair cells in the chicken's cochlea.

Kollmar R R Montgomery L G LG Fak J J Henry L J LJ Hudspeth A J AJ

Proceedings of the National Academy of Sciences of the United States of America 19971201 26

The voltage-gated Ca2+ channels that effect tonic release of neurotransmitter from hair cells have unusual pharmacological properties: unlike most presynaptic Ca2+ channels, they are sensitive to dihydropyridines and therefore are L-type. To characterize these Ca2+ channels, we investigated the expression of L-type alpha1 subunits in hair cells of the chicken's cochlea. In PCRs with five different pairs of degenerate primers, we always obtained alpha1D products, but only once an alpha1C product ...[more]

PMID: 9405708

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Project description:Voltage-dependent Na+ channel activation underlies action potential generation fundamental to cellular excitability. In skeletal and cardiac muscle this triggers contraction via ryanodine-receptor (RyR)-mediated sarcoplasmic reticular (SR) Ca2+ release. We here review potential feedback actions of intracellular [Ca2+] ([Ca2+]i) on Na+ channel activity, surveying their structural, genetic and cellular and functional implications, translating these to their possible clinical importance. In addition to phosphorylation sites, both Nav1.4 and Nav1.5 possess potentially regulatory binding sites for Ca2+ and/or the Ca2+-sensor calmodulin in their inactivating III-IV linker and C-terminal domains (CTD), where mutations are associated with a range of skeletal and cardiac muscle diseases. We summarize in vitro cell-attached patch clamp studies reporting correspondingly diverse, direct and indirect, Ca2+ effects upon maximal Nav1.4 and Nav1.5 currents (Imax) and their half-maximal voltages (V1/2) characterizing channel gating, in cellular expression systems and isolated myocytes. Interventions increasing cytoplasmic [Ca2+]i down-regulated Imax leaving V1/2 constant in native loose patch clamped, wild-type murine skeletal and cardiac myocytes. They correspondingly reduced action potential upstroke rates and conduction velocities, causing pro-arrhythmic effects in intact perfused hearts. Genetically modified murine RyR2-P2328S hearts modelling catecholaminergic polymorphic ventricular tachycardia (CPVT), recapitulated clinical ventricular and atrial pro-arrhythmic phenotypes following catecholaminergic challenge. These accompanied reductions in action potential conduction velocities. The latter were reversed by flecainide at RyR-blocking concentrations specifically in RyR2-P2328S as opposed to wild-type hearts, suggesting a basis for its recent therapeutic application in CPVT. We finally explore the relevance of these mechanisms in further genetic paradigms for commoner metabolic and structural cardiac disease.

Dataset Information

Predominance of the alpha1D subunit in L-type voltage-gated Ca2+ channels of hair cells in the chicken's cochlea.

Publications

Predominance of the alpha1D subunit in L-type voltage-gated Ca2+ channels of hair cells in the chicken's cochlea.

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