Accumulation of Potassium and Calcium in Rat Myocardium Exposed to α-1-Adrenoceptor Stimulation

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