Potassium depolarization of mammalian vestibular sensory cells increases [Ca2+]i through voltage‐sensitive calcium channels |
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Authors: | C Boyer J Lehouelleur & A Sans |
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Institution: | INSERM U‐432, Neurobiologie et Développement du système vestibulaire, UniversitéMontpellier II, CP 089, 34095 Montpellier cedex 05, France |
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Abstract: | The existence of voltage-sensitive Ca2+ channels in type I vestibular hair cells of mammals has not been conclusively proven. Furthermore, Ca2+ channels present in type II vestibular hair cells of mammals have not been pharmacologically identified. Fura-2 fluorescence was used to estimate, in both cell types, intracellular Ca2+ concentration (Ca2+]i) variations induced by K+ depolarization and modified by specific Ca2+ channel agonists and antagonists. At rest, Ca2+]i was 90 ± 20 nm in both cell types. Microperifusion of high-K+ solution (50 mm ) for 1 s increased Ca2+]i to 290 ± 50 nm in type I (n = 20) and to 440 ± 50 nm in type II cells (n = 10). In Ca2+-free medium, K+ did not alter Ca2+]i. The specific L-type Ca2+ channel agonist, Bay K, and antagonist, nitrendipine, modified in a dose-dependent manner the K+-induced Ca2+]i increase in both cell types with maximum effect at 2 μm and 400 nm , respectively. Ni2+, a T-type Ca2+ channel blocker, reduced K+-evoked Ca2+ responses in a dose-dependent manner. For elevated Ni2+ concentrations, the response was differently affected by Ni2+ alone, or combined to nitrendipine (500 nm ). In optimal conditions, nitrendipine and Ni2+ strongly depressed by 95% the Ca2+]i increases. By contrast, neither ω-agatoxin IVA (1 μm ), a specific P- and Q-type blocker, nor ω-conotoxin GVIA (1 μm ), a specific N-type blocker, affected K+-evoked Ca2+i responses. These results provide the first direct evidence that L- and probably T-type channels control the K+-induced Ca2+ influx in both types of sensory cells. |
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Keywords: | calcium channels fura‐2 guinea‐pig type I and type II vestibular hair cells |
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