Myosin light chain kinase controls voltage-dependent calcium channels in vascular smooth muscle

The Ca2+-dependent kinase myosin light chain kinase (MLCK) is the activator of smooth muscle contraction. In addition, it has been reported to be involved in Ca2+ channel regulation in cultured cells, and we previously showed that the MLCK inhibitor ML-7 decreases arginine vasopressin (AVP)-induced Ca2+ influx in rat aorta. This study was designed to investigate whether MLCK is involved in Ca2+ regulation in resistance artery smooth muscle cell, which plays a major role in the control of blood pressure. As ML compounds were shown to have off-target effects, MLCK was downregulated by transfection with a small interfering RNA targeting MLCK (MLCK-siRNA) in rat small resistance mesenteric artery (RMA) and in the rat embryonic aortic cell line A7r5. Noradrenaline-induced contraction and Ca2+ signal were significantly depressed in MLCK-siRNA compared to scramble-siRNA-transfected RMA. Contraction and Ca2+ signal induced by high KCl and voltage-activated Ca2+ current were also significantly decreased in MLCK-siRNA-transfected RMA, suggesting that MLCK depletion modifies voltage-operated Ca2+ channels. KCl- and AVP-induced Ca2+ signals and voltage-activated Ca2+ current were decreased in MLCK-depleted A7r5 cells. Eventually, real-time quantitative PCR analysis indicated that in A7r5, MLCK controlled mRNA expression of Ca(V)1.2 (L-type) and Ca(V)3.1 (T-type) voltage-dependent Ca2+ channels. Our results suggest that MLCK controls the transcription of voltage-dependent Ca2+ channels in vascular smooth muscle cells.