TRPC3 participates in angiotensin II type 1 receptor-dependent stress-induced slow increase in intracellular Ca²⁺ concentration in mouse cardiomyocytes

When a cardiac muscle is held in a stretched position, its [Ca²⁺] transient increases slowly over several minutes in a process known as stress-induced slow increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) (SSC). Transient receptor potential canonical (TRPC) 3 forms a non-selective cation channel regulated by the angiotensin II type 1 receptor (AT1R). In this study, we investigated the role of TRPC3 in the SSC. Isolated mouse ventricular myocytes were electrically stimulated and subjected to sustained stretch. An AT1R blocker, a phospholipase C inhibitor, and a TRPC3 inhibitor suppressed the SSC. These inhibitors also abolished the observed SSC-like slow increase in [Ca²⁺]_i induced by angiotensin II, instead of stretch. Furthermore, the SSC was not observed in TRPC3 knockout mice. Simulation and immunohistochemical studies suggest that sarcolemmal TRPC3 is responsible for the SSC. These results indicate that sarcolemmal TRPC3, regulated by AT1R, causes the SSC.