A Novel Ca_V1.2 N Terminus Expressed in Smooth Muscle Cells of Resistance Size Arteries Modifies Channel Regulation by Auxiliary Subunits*

Voltage-dependent L-type Ca²⁺ (Ca_V1.2) channels are the principal Ca²⁺ entry pathway in arterial myocytes. Ca_V1.2 channels regulate multiple vascular functions and are implicated in the pathogenesis of human disease, including hypertension. However, the molecular identity of Ca_V1.2 channels expressed in myocytes of myogenic arteries that regulate vascular pressure and blood flow is unknown. Here, we cloned Ca_V1.2 subunits from resistance size cerebral arteries and demonstrate that myocytes contain a novel, cysteine rich N terminus that is derived from exon 1 (termed “exon 1c”), which is located within CACNA1C, the Ca_V1.2 gene. Quantitative PCR revealed that exon 1c was predominant in arterial myocytes, but rare in cardiac myocytes, where exon 1a prevailed. When co-expressed with α₂δ subunits, Ca_V1.2 channels containing the novel exon 1c-derived N terminus exhibited: 1) smaller whole cell current density, 2) more negative voltages of half activation (V_1/2,act) and half-inactivation (V_1/2,inact), and 3) reduced plasma membrane insertion, when compared with channels containing exon 1b. β_1b and β_2a subunits caused negative shifts in the V_1/2,act and V_1/2,inact of exon 1b-containing Ca_V1.2α₁/α₂δ currents that were larger than those in exon 1c-containing Ca_V1.2α₁/α₂δ currents. In contrast, β₃ similarly shifted V_1/2,act and V_1/2,inact of currents generated by exon 1b- and exon 1c-containing channels. β subunits isoform-dependent differences in current inactivation rates were also detected between N-terminal variants. Data indicate that through novel alternative splicing at exon 1, the Ca_V1.2 N terminus modifies regulation by auxiliary subunits. The novel exon 1c should generate distinct voltage-dependent Ca²⁺ entry in arterial myocytes, resulting in tissue-specific Ca²⁺ signaling.