The Ca V3.1 T-type Ca 2+channel contributes to voltage-dependent calcium currents in rat outer hair cells

Abstract

Calcium currents through voltage-dependent Ca 2+channels (VDCCs) in mammalian outer hair cells (OHCs) are generally considered to possess the pharmacological properties of L-type (dihydropyridine-sensitive) currents. However, the OHCs' low resting potentials and their slight depolarization upon sound stimuli suggest that the low voltage-activated channels may contribute to Ca 2+regulation. We present morphological and electrophysiological evidence for the presence of the Ca V3.1 T-type Ca 2+channels, one of the low voltage-activated Ca 2+channels, in mature rat OHCs. PCR experiments revealed the expression of Ca V3.1, but not Ca V3.2 or Ca V3.3, in the mature rat cochlea. In situ hybridization and immunohistochemistry revealed expression of Ca V3.1 in both inner and outer hair cells at the mRNA level, but only in the OHCs at the protein level. Western blot analysis of anti-Ca V3.1 antibody showed a 242 kDa band in mature rat cochlear lysates. Patch-clamp recordings of OHCs isolated from rat cochleae after the onset of hearing revealed that whole-cell voltage-dependent Ca 2+ currents were significantly increased in depolarizing steps from a holding potential of − 100 mV when compared with those from − 70 mV. Only the currents from − 100 mV manifested a distinct transient inward Ca 2+ current, and this transient component was effectively blocked by 1 μM of the T-type-specific antagonist, mibefradil. Our data suggest an involvement of Ca V3.1 in intracellular Ca 2+regulation in mature OHCs.