Molecular and pharmacological bases for the gating regulation of L-type voltage-dependent Ca²⁺ channels

Abstract

The voltage-dependent L-type Ca²⁺ channel plays a key role in the spacial and temporal regulation of Ca²⁺. In cardiac excitation-contraction coupling, Ca²⁺-induced Ca²⁺ release (CICR) from ryanodine receptors (RyRs), triggered by Ca²⁺ entry through the nearby L-type Ca²⁺ channel, induces the Ca²⁺-dependent inactivation (CDI) of the Ca²⁺ channel. We demonstrated that the CICR-dependent CDI of L-type Ca²⁺ channels, under control of the privileged cross-signaling between L-type Ca²⁺ channels and RyRs, plays important roles for monitoring and tuning the SR Ca²⁺ content via changes of AP waveform and the amount of Ca²⁺-influx during AP in ventricular myocytes. L-type Ca²⁺ channels are modulated by the binding of Ca²⁺ channel antagonists and agonists to the pore-forming α_1C subunit. We identified Phe¹¹¹² and Ser¹¹¹⁵ in the pore-forming IIIS5-S6 linker region of the α_1C subunit as critical determinants of the binding of dihydropyridines (DHP). Interestingly, double mutant Ca²⁺ channel (F1112A/S1115A) failed to discriminate between a DHP Ca²⁺ channel agonist and antagonist stereoisomers. We proposed that Phe¹¹¹² and Ser¹¹¹⁵ in the pore-forming IIIS5-S6 linker region is required for the stabilization of the Ca²⁺ channel in the open state by Ca²⁺ channel agonists and further proposed a novel model for the DHP-binding pocket of the α_1C subunit. These integrative studies on the gating regulation of cardiac L-type Ca²⁺ channels will provide the molecular basis for the pharmacology of Ca²⁺ channel modulators.