THE NA+ K+ ATPASE MEDIATES THE ALPHA(1)-ADRENOCEPTOR STIMULATED INCREASE IN RB-86(+)-UPTAKE IN ISOLATED VENTRICULAR CARDIOMYOCYTES FROM ADULT-RAT HEART/

The aim of the present study was to identify the mechanism(s) responsi ble for the alpha(1)-adrenoceptor stimulated increase in potassium upt ake in ventricular cardiomyocytes isolated from adult rat heart. The N a-/K(-)ATPase blocker ouabain the Na-/K-/2Cl(-)-cotransporter blocker bumetanide, the Na-/H+-exchanger blocker HOE 694 and the potassium cha nnel blocker 4-aminopyridine were used as experimental tools. Rb-86(-) was used as potassium analogue. The basal Rb-86(-)-uptake rate was 0. 25+/-0.01 ml/g protein x min. Maximal alpha(1)-adrenoceptor stimulatio n increased the Rb-86(+)-uptake 38+/-2 %. Ouabain dose dependently eli minated the alpha(1)-adrenoceptor stimulated response with a -logIC(50 )-value of 3.64+/-0.23. Bumetanide did not affect the stimulated respo nse, and there was no effect of bumetanide on the ouabain sensitive co mponent. HOE 694 and 4-aminopyridine had no effect on the stimulated R b-86(+)-uptake. Ouabain and HOE 694 also dose dependently inhibited a portion of the basal Rb-86(+)-uptake (about 60 % and 20 %, respectivel y), but there was no effect of bumetanide or 4-aminopyridine on the ba sal Rb-86(+)-uptake. The results show that the Na+/K+ ATPase alone med iates the alpha(1)-adrenoceptor stimulated increase in potassium uptak e in this preparation of ventricular cardiomyocytes isolated from adul t rat heart.