Unidirectional sodium and potassium flux in myogenic L6 cells: mechanisms and volume-dependent regulation

Abstract

To clarify the relative participation of particular ion transport systems in net univalent cation fluxes under basal conditions and altered volume of skeletal muscle-derived cells, the effect of inhibitors of the Na(+)-K+ pump (ouabain), univalent ion cotransporters [bumetanide, furosemide, and (dihydroindenyl)oxy alkanoic acid], and N+/H+ exchanger (ethylisopropylamiloride) on 86Rb and 22Na fluxes has been studied in L6 myoblasts incubated in isosmotic (320 mosmol/kg) and anisosmotic media. Under the isosmotic condition, the relative contribution of ouabain-inhibited and ouabain-insensitive bumetanide-inhibited component of 86Rb influx was approximately 15–20 and 60%, respectively. 22Na influx was inhibited by bumetanide and ethylisopropylamiloride by 25 and 15%, respectively. Under isosmotic conditions, an increase of L6 cell volume was observed after addition of extracellular acetylcholine, extracellular K(+)-induced depolarization, or lowering of the pH of the incubation medium. High extracellular glutathione (150 microM) did not affect the cell volume of the muscle-derived cells bathed in isosmotic medium. Results of this study suggest that the bumetanide-inhibited component of K+ influx plays a key role in the adjustment of transmembrane K+ gradient in L6 myoblasts. The Na+/H+ exchanger appears to be important in regulatory volume increase.