The voltage‐dependent L‐type Ca²⁺ (Ca_V1.2) channel C‐terminus fragment is a bi‐modal vasodilator

Abstract

Key points Voltage‐dependent L‐type Ca 2+ (Ca V 1.2) channels are the major Ca 2+ influx pathway and are central to contractility regulation in arterial smooth muscle cells. Ca V 1.2 exists as a full‐length channel and undergoes cleavage to a short Ca V 1.2 and a C‐terminus (CCt) fragment in rat and human arterial smooth muscle cells. CCt decreases Ca V 1.2 transcription and shifts the voltage dependence of current activation and inactivation to more depolarized potentials in arterial smooth muscle cells. CCt reduces pressure‐ and depolarization‐induced vasoconstriction. CCt is a bi‐modal vasodilator. Abstract Voltage‐dependent L‐type Ca 2+ channels (Ca V 1.2) are the primary Ca 2+ entry pathway in vascular smooth muscle cells (myocytes). Ca V 1.2 channels control systemic blood pressure and organ blood flow and are pathologically altered in vascular diseases, which modifies vessel contractility. The Ca V 1.2 distal C‐terminus is susceptible to proteolytic cleavage, which yields a truncated Ca V 1.2 subunit and a cleaved C‐terminal fragment (CCt). Previous studies in cardiac myocytes and neurons have identified CCt as both a transcription factor and Ca V 1.2 channel inhibitor, with different signalling mechanisms proposed to underlie some of these effects. CCt existence and physiological functions in arterial myocytes are unclear, but important to study given the functional significance of Ca V 1.2 channels. Here, we show that CCt exists in myocytes of both rat and human resistance‐size cerebral arteries, where it locates to both the nucleus and plasma membrane. Recombinant CCt expression in arterial myocytes inhibited Ca V 1.2 transcription and reduced Ca V 1.2 protein. CCt induced a depolarizing shift in the voltage dependence of both Ca V 1.2 current activation and inactivation, and reduced non‐inactivating current in myocytes. Recombinant truncated CCt lacking a putative nuclear localization sequence (Δ92CCt) did not locate to the nucleus and had no effect on arterial Ca V 1.2 transcription or protein. However, Δ92CCt shifted the voltage dependence of Ca V 1.2 activation and inactivation similarly to CCt. CCt and Δ92CCt both inhibited pressure‐ and depolarization‐induced vasoconstriction, although CCt was a far more effective vasodilator. These data demonstrate that endogenous CCt exists and reduces both Ca V 1.2 channel expression and voltage sensitivity in arterial myocytes. Thus, CCt is a bi‐modal vasodilator.