Hydrogen sulfide is a partially redox-independent activator of the human jejunum Na+ channel, Nav1.5

Abstract

Hydrogen sulfide (H2S) is produced endogenously by l-cysteine metabolism. H2S modulates several ion channels with an unclear mechanism of action. A possible mechanism is through reduction-oxidation reactions attributable to the redox potential of the sulfur moiety. The aims of this study were to determine the effects of the H2S donor NaHS on NaV1.5, a voltage-dependent sodium channel expressed in the gastrointestinal tract in human jejunum smooth muscle cells and interstitial cells of Cajal, and to elucidate whether H2S acts on NaV1.5 by redox reactions. Whole cell Na+ currents were recorded in freshly dissociated human jejunum circular myocytes and NaV1.5-transfected human embryonic kidney-293 cells. RT-PCR amplified mRNA for H2S enzymes cystathionine β-synthase and cystathionine γ-lyase from the human jejunum. NaHS increased native Na+ peak currents and shifted the half-point ( V1/2) of steady-state activation and inactivation by +21 ± 2 mV and +15 ± 3 mV, respectively. Similar effects were seen on the heterologously expressed NaV1.5 α subunit with EC50s in the 10−4 to 10−3 M range. The reducing agent dithiothreitol (DTT) mimicked in part the effects of NaHS by increasing peak current and positively shifting steady-state activation. DTT together with NaHS had an additive effect on steady-state activation but not on peak current, suggesting that the latter may be altered via reduction. Pretreatment with the Hg2+-conjugated oxidizer thimerosal or the alkylating agent N-ethylmaleimide inhibited or decreased NaHS induction of NaV1.5 peak current. These studies show that H2S activates the gastrointestinal Na+ channel, and the mechanism of action of H2S is partially redox independent.