The mechanisms of action of noradrenaline on ouabain-sensitive rubidium uptake in guinea-pig myocardium

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Abstract
The mechanism by which noradrenaline stimulates ouabain-sensitive rubidium uptake in guinea-pig myocardial tissue has been studied. The stimulatory action of low concentrations of noradrenaline was reversed by high doses of propranolol (10-5 mol/l) in atrial tissue, but was not reversed by .alpha.- or .beta.-, or combined .alpha.- and .beta.-adrenoceptor antagonists in ventricular tissue. Rubidium uptake was also found to increase with increasing extracellular potassium concentration ([K]o). The percentage values of stimulation by noradrenaline decreased with increasing [K]o. Noradrenaline had no effect on the rate of ATP splitting by an isolated membrane preparation of Na,K-ATPase. It is proposed that noradrenaline stimulates active cation transport by either (a) an effect secondary to increased passive efflux of K ions, or (b) an action at a novel adrenergic receptor, distinct from the ATPase enzyme itself.