INCREASED INTRACELLULAR POTASSIUM AND WATER CONTENTS IN RAT-HEART AFTER ALPHA-1-ADRENOCEPTOR STIMULATION

Potassium accumulation in rat heart after alpha-1-adrenoceptor stimula tion has previously been reported from indirect measurements. Here we present data on intracellular potassium content measured directly in t he heart. Isolated rat hearts perfused in a non-recirculating system w ere exposed to alpha-1-adrenoceptor stimulation (5 X 10(-5) mol/l phen ylephrine in the presence of 10(-6) mol/l timolol). C-14-Sucrose was u sed to estimate the extracellular space. From heart homogenates intrac ellular potassium, magnesium and cellular water contents were determin ed and the ion concentrations calculated accordingly. The intracellula r magnesium content remained unchanged during all experimental conditi ons. alpha-1-Adrenoceptor stimulation evoked an increase in potassium content by 9% (4, 14; 95% confidence interval (CI), P=0.0006). Due to an observed increase in intracellular water by 17% (9, 26; 95% CI, P=0 .0006), the potassium concentration apparently decreased by 8% (0.3, 1 5; 95% CI, P=0.04). During partial inhibition of the Na+/K+-ATPase by 10(-5) mol/l ouabain, there was an increase in potassium content by 5% (1, 9; 95% CI, P=0.008). There was, however, no significant increase in intracellular water in this situation. Calculated intracellular pot assium concentration showed accordingly a slight increase. The effects upon potassium and water both in the absence and presence of ouabain were eliminated by the alpha-1-adrenoceptor blocker prazosin (10(-6) m ol-l). alpha-1-Adrenoceptor stimulation apparently increased cellular dry weight by 10% (2, 18; 95% CI, P=0.02). Changes in translocation of potassium and water must be considered as part of the alpha-1-adrener gic heart effects.