Molecular Determinants of Ca2 Potentiation of Diltiazem Block and Ca2-Dependent Inactivation in the Pore Region of

Diltiazem block of Cav1.2 is frequency-dependent and poten-tiated by Ca2. We examined the molecular determinants of these characteristics using mutations that affect Ca2 interac-tions with Cav1.2. Mutant and wild-type (WT) Cav1.2 channels were transiently expressed in tsA 201 cells with 1b and 2 subunits. The four conserved glutamates that compose the Ca2 selectivity filter in Cav1.2 were mutated to Gln (E363Q, E709Q, E1118Q, E1419Q), and each single mutant was as-sayed for block by diltiazem using whole-cell voltage-clamp recordings in either 10 mM Ba2 or 10 mM Ca2. In Ba2, none of the mutations affected the potency of diltiazem block of closed channels (0.05 Hz stimulation). However, frequency-dependent block (1Hz stimulation) was eliminated in the mutant E1419Q (domain IV), which recovered more rapidly than W