SCN5A mutation G615E results in Na_V1.5 voltage-gated sodium channels with normal voltage-dependent function yet loss...

SCN5A is expressed in cardiomyocytes and gastrointestinal (GI) smooth muscle cells (SMCs) as the voltage-gated mechanosensitive sodium channel Na_V1.5. The influx of Na⁺ through Na_V1.5 produces a fast depolarization in membrane potential, indispensable for electrical excitability in cardiomyocytes and important for electrical slow waves in GI smooth muscle. As such, abnormal Na_V1.5 voltage gating or mechanosensitivity may result in channelopathies. SCN5A mutation G615E - found separately in cases of acquired long-QT syndrome, sudden cardiac death, and irritable bowel syndrome - has a relatively minor effect on Na_V1.5 voltage gating. The aim of this study was to test whether G615E impacts mechanosensitivity. Mechanosensitivity of wild-type (WT) or G615E-Na_V1.5 in HEK-293 cells was examined by shear stress on voltage- or current-clamped whole cells or pressure on macroscopic patches. Unlike WT, voltage-clamped G615E-Na_V1.5 showed a loss in shear- and pressure-sensitivity of peak current yet a normal leftward shift in the voltage-dependence of activation. In current-clamp, shear stress led to a significant increase in firing spike frequency with a decrease in firing threshold for WT but not G615E-Na_V1.5. Our results show that the G615E mutation leads to functionally abnormal Na_V1.5 channels, which cause disruptions in mechanosensitivity and mechano-electrical feedback and suggest a potential contribution to smooth muscle pathophysiology.