INSULIN ACTIVATES FUROSEMIDE-SENSITIVE K- UPTAKE SYSTEM IN BC(3)H1 CELLS( AND CL)

Insulin augments the activity of Na+-K+-adenosinetriphosphatase (ATPas e) in skeletal muscles. This study shows that when furosemide- and bum etanide-inhibitable Rb-86(+) uptake is measured in the skeletal muscle -like BC(3)H1 cell line, insulin and insulin-like growth factor I (IGF -I) activate a loop diuretic-sensitive K+ and Cl- transport system but have no effect on Na+-K+-ATPase. The insulin-stimulated K+ transport system is extracellular Na+ concentration ([Na+](o)) independent and e xtracellular Cl- concentration ([Cl-](o)) dependent. Na+-independent K +-Cl- cotransport systems have been identified in other cells, but the ir sensitivity to insulin or growth factors has not been described. Th e affinities of the insulin-stimulated K+ uptake in BC(3)H1 cells for K+ (0.9 +/- 0.1 mM) and loop diuretics (5.9 x 10(-7) and 10(-7) M for furosemide and bumetanide, respectively) are higher than those of K+-C l- cotransporters in other cells. Thus the insulin-stimulated K+ and C l- transport system in BC(3)H1 seems kinetically different from K+-Cl- cotransporters in other cells. Insulin and IGF-I may activate a uniqu e K+-Cl- cotransporter or activate a [Na+](o)-independent K+-Cl- cotra nsport mode of Na+-K+-Cl- cotransporter in BC(3)H1 cells.