Reversible stimulation of the Na+/K+ pump by monensin in cultures of vascular smooth muscle

Abstract

Two ionophores, monensin and salinomycin, increased total cell Na+ and ouabain-sensitive 86Rb+ uptake in cultures of smooth muscle cells from rat aorta. Monensin was used to produce graded increases in cell Na+ in order to assess the Na+ dependence of the Na+/K+ pump in the intact cell. The relationship between internal Na+ and ouabain-sensitive 86Rb+ uptake was hyperbolic (K'Na = 3 mM). Monensin did not stimulate 86Rb+ uptake in the absence of external Na+. Loading the cells with Na+ by exposing cultures to a K+-free medium for 3 hr maximally increased cell Na+ and ouabain-sensitive 86Rb+ uptake to the same extent as monensin. Total cell Na+ and pump activity in monensin-treated cells returned to the initial values after removing the ionophore. Monensin was then able to increase total cell Na+ and ouabain-sensitive 86Rb+ uptake to the same extent as the initial treatment with the ionophore.