Calcium Currents in Hair Cells Isolated from Semicircular Canals of the Frog


AbstractL-type and R-type Ca2+ currents were detected in frog semicircular canal hair cells. The former was noninactivating and nifedipine-sensitive (5μM); the latter, partially inactivated, was resistant to ω-conotoxin GVIA (5μM), ω-conotoxin MVIIC (5μM), and ω-agatoxin IVA (0.4μM), but was sensitive to mibefradil (10μM). Both currents were sensitive to Ni2+ and Cd2+ (>10μM). In some cells the L-type current amplitude increased almost twofold upon repetitive stimulation, whereas the R-type current remained unaffected. Eventually, run-down occurred for both currents, but was prevented by the protease inhibitor calpastatin. The R-type current peak component ran down first, without changing its plateau, suggesting that two channel types generate the R-type current. This peak component appeared at −40mV, reached a maximal value at −30mV, and became undetectable for voltages ≥0mV, suggestive of a novel transient current: its inactivation was indeed reversibly removed when Ba2+ was the charge carrier. The L-type current and the R-type current plateau were appreciable at −60mV and peaked at −20mV: the former current did not reverse for voltages up to +60mV, the latter reversed between +30 and +60mV due to an outward Cs+ current flowing through the same Ca2+ channel. The physiological role of these currents on hair cell function is discussed

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Last time updated on 6/5/2019

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