Coronary hypercontractility to acidosis owes to the greater activity of TMEM16A/ANO1 in the arterial smooth muscle cells

Background: Severe acidosis deteriorates cardiac injury. Rat coronary arteries (RCAs) are unusually hypercontractive to extracellular (o) acidosis (EA). TMEM16A-encoded anoctamin 1 (ANO1), a Ca2+-activated chloride channel (CaCC), plays an important role in regulating coronary arterial tension. Purpose: We tested the possibility that the activation of CaCCs in the arterial smooth muscle cell (ASMC) contributes to EA-induced RCA constriction. Methods: ANO1 expression was detected with immunofluorescence staining and Western blot. TMEM16A mRNA was assessed with quantitative Real-Time PCR. Cl- currents and membrane potentials were quantified with a patch clamp. The vascular tension was recorded with a myograph. Intracellular (i) level of Cl- and Ca2+ was measured with fluorescent molecular probes. Results: ANO1 was expressed in all tested arterial myocytes, but was much more abundant in RCA ASMCs as compared with ASMCs isolated from rat cerebral basilar, intrarenal and mesenteric arteries. EA reduced [Cl-]i levels, augmented CaCC currents exclusively in RCA ASMCs and depolarized RCA ASMCs to a greater extent. Cldeprivation, which depleted [Cl-]i by incubating the arteries or their ASMCs in Cl--free bath solution, decreased EA-induced [Cl-]i reduction, diminished EA-induced CaCC augmentation and time-dependently depressed EAinduced RCA constriction. Inhibitor studies showed that these EA-induced effects including RCA constriction, CaCC current augmentation, [Cl-]i reduction and/or [Ca2+]i elevation were depressed by various Cl- channel blockers, [Ca2+]i release inhibitors and L-type voltage-gated Ca2+ channel inhibitor nifedipine. ANO1 antibody attenuated all observed changes induced by EA in RCA ASMCs. Conclusion: The greater activity of RCA ASMC CaCCs complicated with an enhanced Ca2+ mobilization from both [Ca2+]i release and [Ca2+]o influx plays a pivotal role in the distinctive hypercontractility of RCAs to acidosis. Translation of these findings to human beings may lead to a new conception in our understanding and treating cardiac complications in severe acidosis.