Variable Contribution of TMEM16A to Tone in Murine Arterial Vasculature

Abstract

TMEM16A is essential for Ca²⁺ -activated Cl^- conductance in vascular smooth muscle. The importance of TMEM16A for agonist-induced vascular constriction and blood pressure control is, however, under debate. Previous studies suggested that TMEM16A might have a complex cellular function beyond being essential for the Ca²⁺ -activated Cl^- conductance, for example modulation of Ca²⁺ channel expression. Mice with constitutive, smooth muscle-specific expression of siRNA directed against Tmem16a (transgenic mice, TG) were generated. Isometric constrictions of isolated aorta, mesenteric, femoral and tail arteries from TG mice were compared with wild-types. Protein expression was analysed by Western blots. Blood pressure and heart rate were studied telemetrically. Significant TMEM16A down-regulation was seen in aorta and tail arteries, while no changes were detected in mesenteric and femoral arteries. Contractile responses of mesenteric and femoral arteries from TG and wild-type mice were not different. Aorta from TG mice showed reduced agonist-induced constriction, while their responses to elevated K⁺ were unchanged. Tail arteries from TG mice also constricted less to adrenergic stimulation than wild-types. Surprisingly, tail arteries from TG mice constricted less to elevated K⁺ too and were more sensitive to nifedipine-induced relaxation. Consistently, TMEM16A down-regulation in tail arteries was associated with reduction in CACNA1C protein (i.e. vascular L-type Ca²⁺ channel) expression. No differences in blood pressure and heart rate between the groups were seen. This study suggests a complex contribution of TMEM16A in vascular function. We suggest that TMEM16A modulates arterial contractility, at least in part, indirectly via regulation of CACNA1C expression.