The effect of catecholamines on Na—K transport and membrane potential in rat soleus muscle

Publisher Website
Google Scholar
Abstract
In a substrate-free Krebs-Ringer bicarbonate buffer adrenaline (ADR [epinephrine]) (6 .times. 10-6 M) increased 22Na efflux by 83%, 42K influx by 34% and EM [resting membrane potential] by 10%. Similar effects were exerted by noradrenaline (NA [epinephrine]), phenylephrine, salbutamol and isoprenaline. The effects of ADR on Na-K transport and EM were suppressed by ouabain (10-3 M) and propranolol (10-5 M), but not by thymoxamine (10-5 M) or tetracaine (10-4 M). Following 90 min of incubation in the presence of ADR (6 .times. 10-6 M), the intracellular K/Na-ratio was increased 3-fold. NA produced almost the same change, and both catecholamines induced a new steady-state distribution of Na and K which could be maintained for several hours in vitro. The effect of ADR on 22Na efflux and EM could be detected at concentrations down to 6 .times. 10-9 and 6 .times. 10-10 M, respectively, and half maximum increase was obtained at around 2 .times. 10-8 M. NA was at least 1 order of magnitude less potent. The effect of low concentrations of ADR on 22Na efflux was potentiated by theophylline (2 m M). When added together, dibutyryl-cyclic AMP and theophylline mimicked the action of ADR on 22Na efflux, 42K influx, Na/K content and EM. Ouabain (10-3 M) also suppressed the effect of dibutyryl-cyclic AMP and theophylline on Na-K transport. Following the addition of ouabain (10-3 M), EM rapidly dropped from a mean of -71 to -63 mV, and then showed a slow linear fall for up to 4h. The hyperpolarization induced by ADR was associated with a decrease in membrane conductance, 22Na influx and 42K efflux. The time course and the response to ouabain suggested that all of these effects were secondary to stimulation of the active coupled transport of Na and K. In rat soleus muscle, the active Na-K transport was electrogenic and susceptible to stimulation by catecholamines via .beta. adrenoceptors. This effect was mediated by adenylate cyclase activation and may account for the increase in EM and the intracellular K/Na ratio.

This publication has 35 references indexed in Scilit: