Role of Nitric Oxide in the Regulation of Mechanosensitive Ionic Channels in Cardiomyocytes: Contribution of NO-Synthases

The role of NO in the regulation of currents passing through ion channels activated by cell stretching (mechanically gated channels, MGC), particularly through cation-selective K+-channels TRPC6, TREK1 (K2P2.1), and TREK2 (K2P10.1), was studied on isolated mouse, rat, and guinea pig cardiomyocytes using whole-cell patch-clamp technique. In non-deformed cells, binding of endogenous NO with PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline- 1-1-oxy-3-oxide) irreversibly shifted the diastolic membrane potential towards negative values, modulates Kir-channels by reducing IK1, and blocks MGC. Perfusion of stretched cells with PTIO solution completely blocked MG-currents. NO-synthase inhibitors L-NAME and L-NMMA completely blocked MGC. Stretching of cardiomyocytes isolated from wild type mice and from NOS1–/–- and NOS2–/–- knockout mice led to the appearance in MG-currents typical for the specified magnitude of stretching, while stretching of cardiomyocytes from NOS3–/–- knockout mice did not produce in MG-current. These findings suggest that NO plays a role in the regulation of MGC activity and that endothelial NO-synthase predominates as NO source in cardiomyocyte response to stretching.