A kinetic analysis of the facilitatory action of adrenaline

The 22Na+-efflux from skeletal muscle cells of frog (Rana nigromaculata) was measured in Ringer solutions containing different concentrations of K+ (0.1 to 30 mM). The effects of adrenaline (30 microM) and ouabain (10 microM) on the 22Na+-efflux were investigated for the purpose to clarify the mechanism of the facilitatory effect of adrenaline on Na+ - K+ pump. The rate coefficient for the ouabain-sensitive 22 Na+-efflux increases with increasing extracellular K+ concentrations and adrenaline potently facilitates these rate coefficients. On the basis of Michaelis-Menten type kinetics assumed for the reaction between pump site and extracellular K+, it is concluded that adrenaline decreases the dissociation constant (Km), and increases the maximum Na+-efflux.