Calcium currents in mouse inner hair cells (IHC) are carried predominantly by the Ca_v1.3 subtype of L-type voltage gated calcium channels. They differ from Ca_v1.2 channels in many aspects including differential pharmacological properties. We investigated the effect of phenylalkylamine (PAA) verapamil and benzothiazepines (BTZ) diltiazem and gallopamil on the Ca²⁺ currents in mouse IHCs. We recorded calcium currents of IHCs in acute preparations of the organ of Corti (age: P3-P7) by using the whole-cell configuration of the patch-clamp method with 5 mM Ca²⁺ as charge carrier. Both PAA and BTZs inhibited about 90 % of the current at the concentration of 3 mM. This effect was largely reversible. For verapamil, IC₅₀ was 199 ± 19 mM and the Hill coefficient was 0.64 ± 0.02. For diltiazem IC₅₀ was 334 ± 52 mM and for gallopamil 467 ± 151 mM. Corresponding Hill coefficients were 0.98 ± 0.12 and 0.84 ± 0.20, respectively.

These concentrations were similar to those needed to block recombinant Ca_v1.2 channels (Lacinova et al., J. Pharmacol. Exp. Ther. 1995) or L-type, supposedly Ca_v1.3 Ca²⁺ channels in turtle hair cells (Schnee and Ricci, J. Physiol. 2003). Supported by the EU Marie-Curie Trainings Site programme.