Calcium and Energy Requirements for K+ Release Mediated by the Epinephrine α-Receptor in Rat Parotid Slices

Abstract

Calcium was essential for the K+ release mediated by the epinephrine α-receptor in rat parotid slices. The pattern of K+ release was the same, whether calcium or epinephrine was added as the last component. Mg2+ appeared to compete with Ca2+ and partially inhibited K+ release. Reuptake of K+ into the slices could be initiated either by chelation of the Ca2+ with ethylene glycol bis(β-aminoethyl ether)-N,N′-tetraacetic acid or by inhibition of the epinephrine α-receptor with phentolamine. It was therefore concluded that both Ca2+ and epinephrine are required not only to initiate the reaction but also to maintain it. Ouabain, an inhibitor of the Na+,K+-activated ATPase prevented the reuptake of K+. This inhibitor enhanced K+ release caused by epinephrine but did not induce K+ release in absence of the hormone. It is suggested that the extent of K+ release is the resultant of efflux mediated by the epinephrine α-receptor and influx mediated by the Na+, K+-activated ATPase. It is concluded that energy is required for the epinephrine-induced K+ release since dinitrophenol as well as a nitrogen atmosphere inhibited K+ efflux from the slices.