An analysis of the effect of adrenaline on electrogenic Na+ pump of visceral nerve fibers in bullfrogs.

The effect of adrenaline (Ad) on the electrogenic Na+ pump of bullfrog visceral nerve fibers was studied, by testing the effect of this drug on the K-activated hyperpolarization (KAH) of these nerve fibers. KAHs were recorded by adding K (0.2--5 mM) to an extracellular K-free solution with which preparations were previously perfused and the actual KAH amplitude (net KAH) was estimated by taking into account the amplitude of membrane depolarization induced by K in the presence of ouabain (0.001 mM). The dose-response relation between K concentrations and net KAHs follows Michaelis-Menten kinetics; the log dose-response relation showed a sigmoid curve and the Lineweaver-Burk Plot of dose-response relation showed a straight line when nH=1.3. The net KAH was augmeted by Ad (0.03--1 mM); facilitative effects of three kinds of catecholamine on the net KAH were Ad greater than noradrenaline greater than isopreterenol. The log dose-response curve was shifted to the left in parallel in the presence of Ad; the Lineweeather-Burk plot showed a straight line when nH=1.3 and this line met the control line at the ordinate point where K concentration is infinitive, while the apparent dissociation constant (Km) decreased to 0.82 from 1.3 mM (control) in the presence of 0.3 mM Ad. Net KAH was augmented by the removal of extracellular Cl or by the action of TEA; the membrane resistance was expected to increase under these experimental conditions. The dose-response relation obtained under these conditions showed an increase of maximum response without changes in Km value. It was concluded on the basis of the present results that the increase in net KAH by Ad was due to an increase in the electrogenic Na+ pump current. The mechanism underlying such an Ad action was discussed, and it was suggested that the rate of the electrogenic Na+ pump was increased by the action of Ad.