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

Abstract

SCN5A is expressed in cardiomyocytes and gastrointestinal (GI) smooth muscle cells (SMCs) as the voltage-gated mechanosensitive sodium channel Na V 1.5. The influx of Na + through Na V 1.5 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 V 1.5 voltage gating or mechanosensitivity may result in channelopathies. SCN5A mutation G615Efound separately in cases of acquired long-QT syndrome, sudden cardiac death, and irritable bowel syndromehas a relatively minor effect on Na V 1.5 voltage gating. The aim of this study was to test whether G615E impacts mechanosensitivity. Mechanosensitivity of wild-type (WT) or G615E-Na V 1.5 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 V 1.5 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 V 1.5. Our results show that the G615E mutation leads to functionally abnormal Na V 1.5 channels, which cause disruptions in mechanosensitivity and mechano-electrical feedback and suggest a potential contribution to smooth muscle pathophysiology.

Mechanotransduction in gastrointestinal smooth muscle cells: role of mechanosensitive ion channels

“…Indeed, in human GI SMCs, the influx of Na þ through Na V 1.5 quickly depolarizes the membrane potential, which was found to be important for the regulation of the electrical slow waves in GI smooth muscle (100). Na V 1.5 is also mechanosensitive (22,101,102). Mechanical forces have several important effects on Na V 1.5, including their gating, kinetics, and inactivation (22,53).…”

“…Perhaps most importantly, human SCN5A mutations are associated with multiple clinical phenotypes, including conduction disorders in the heart and irritable bowel syndrome (IBS) in the GI tract (104,105). IBS-associated SCN5A mutations frequently impact voltage gating (106) and/or mechanosensitivity (101,102).…”

Capsaicin alters human NaV1.5 mechanosensitivity

“…These complementary techniques allow us to highlight different aspects of the channels' mechanosensitivity due to both techniques' intrinsic strengths and weaknesses. 11,[21][22][23] The effect of pressure was tested in a pairwise fashion 1,11,14 , with pressure at 0 or -30 mmHg applied at each voltage step (Figure 2A,C,E-H). Whole-cell current responses to shear was tested by perfusion at 0 or 10 mL/min (Figure 2B,D,E-H In the absence of drug, pressure and shear accelerated Na + current activation, decreasing the activation constant (τACT) by 20.0±5.3% or 20.4±3.3%, respectively (n = 12-14, P<0.05 to no force controls; Figure 2F).…”

“…These complementary techniques allow us to highlight different aspects of the channels' mechanosensitivity due to both techniques' intrinsic strengths and weaknesses. 11,[21][22][23] The effect of pressure was tested in a pairwise fashion 1,11,14 , with pressure at 0 or -30 mmHg applied at each voltage step (Figure 2A,C,E-H). Whole-cell current responses to shear was tested by perfusion at 0 or 10 mL/min (Figure 2B,D,E-H).…”

“…6,7 Many SCN5A mutations lead to voltage-gating abnormalities, some associated with abnormal responses to mechanical stimuli. [7][8][9][10] Impaired stretch modulation in NaV1.5, for example, occurs in some mutations that also cause LQT3-type cardiac arrhythmias, 8,11 and some mutations that lead to altered NaV1.5 MS are found in patients with IBS. 10,12 Because of their involvement in many diseases, ion channels are prime targets for pharmacological treatment.…”