Accumulation of potassium and calcium in rat myocardium exposed to alpha-1-adrenoceptor stimulation.

Net fluxes of potassium, calcium, sodium and chloride were examined in isolated perfused rat hearts during alpha-1-adrenoceptor stimulation. The ion measurements were performed in the non-recirculating perfusate. Hearts were exposed to alpha-1-adrenoceptor stimulation (phenylephrine 5 x 10(-5) mol/l in the presence of the beta-blocker timolol 10(-6) mol/l). During alpha-1-adrenoceptor stimulation perfusate potassium fell relatively rapidly by about 0.10 mmol/l after approximately 100 sec. followed by a slower rise. About 180 sec. after onset of alpha-1-adrenoceptor stimulation, the potassium level was about 0.06 mmol/l below the control concentration level. This reduction was eliminated by the alpha-1-adrenoceptor blocker prazosin (10(-7) mol/l). The effects on net calcium fluxes were measured at two different calcium concentrations. For both concentrations we found a small but statistically significant reduction of the calcium concentration in the perfusate after alpha-1-adrenoceptor stimulation. Neither sodium nor chloride perfusate concentrations showed statistical significant changes compared to control values. The present observations revealed the existence of alpha-1-adrenoceptor regulated mechanisms related to a net uptake of both potassium and calcium in rat heart.