The effect of cAMP on the activity of Na(+)-K(+) ATPase in the rat jejunum was studied by measuring the ouabain-sensitive (86)Rb accumulation by isolated villus cells. The cyclic nucleotide increased significantly (86)Rb accumulation by the enterocytes. The involvement of the NaKCl(2) symporter, the H(+)-K(+) exchanger and the Na(+)-K(+) pump was tested by measuring, respectively the furosemide-sensitive, the omeprazole sensitive, and the ouabain-sensitive (86)Rb accumulation. Furosemide significantly increased the basal level of intracellular (86)Rb and exerted overlapping effects with cAMP. Inhibiting the Na(+)-H(+) exchanger with amiloride, decreased the basal level of intracellular (86)Rb, and in its presence the stimulatory effect of cAMP was still observed but not that of furosemide. cAMP and furosemide did not exert any significant effect on (86)Rb accumulation by the enterocytes in presence of ouabain or in the absence of sodium but their stimulatory effect still appeared in the absence of chloride or in the presence of omeprazole or K(+)-channel blockers. These data suggest that cAMP and furosemide stimulate the Na(+)-K(+) ATPase in rat jejunal cells, and that this effect is, in the case of furosemide, mediated by an activation of the Na(+)-H(+) exchanger.
Copyright 2000 Academic Press.