Details

Autor(en) / Beteiligte

• Martini, M.
• Rossi, M.L.
• Rubbini, G.
• Rispoli, G.

Titel

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

Ist Teil von

• Biophysical journal, 2000-03, Vol.78 (3), p.1240-1254

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2000

Quelle

Electronic Journals Library

Beschreibungen/Notizen

• L-type and R-type Ca 2+ currents were detected in frog semicircular canal hair cells. The former was noninactivating and nifedipine-sensitive (5 μM); the latter, partially inactivated, was resistant to ω-conotoxin GVIA (5 μM), ω-conotoxin MVIIC (5 μM), and ω-agatoxin IVA (0.4 μM), but was sensitive to mibefradil (10 μM). Both currents were sensitive to Ni 2+ and Cd 2+ (>10 μM). 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 −40 mV, reached a maximal value at −30 mV, and became undetectable for voltages ≥0 mV, suggestive of a novel transient current: its inactivation was indeed reversibly removed when Ba 2+ was the charge carrier. The L-type current and the R-type current plateau were appreciable at −60 mV and peaked at −20 mV: the former current did not reverse for voltages up to +60 mV, the latter reversed between +30 and +60 mV due to an outward Cs + current flowing through the same Ca 2+ channel. The physiological role of these currents on hair cell function is discussed.