Active Na—K transport and the rate of ouabain binding. The effect of insulin and other stimuli on skeletal muscle and adipocytes

Abstract

The effect of stimulation or inhibition of active Na-K transport on [3H]ouabain binding was investigated in isolated soleus muscles and adipocytes. In rat soleus muscle, the ouabain-sensitive component of 42K influx was stimulated by insulin (100 mu[milliunits]ml), adrenaline [epinephrine] (6 .times. 10-6 M), and by pre-incubation with veratrine (10-5 M) or in a K-free buffer. In all of these instances, the rate of ouabain binding was increased by 41-113%. Conversely, pre-treatment with tetracaine (0.2 mM) decreased the 42K-influx and diminished the rate of [3H]ouabain binding by 36%. Neither insulin, adrenaline or tetracaine produced any detectable change in the total number of ouabain-binding sites (as measured under equilibrium conditions) in rat soleus muscle. In mouse and guinea-pig soleus muscle and in fat cells isolated from rats, insulin also increased the rate of [3H]ouabain binding without producing any significant change in the total number of ouabain-binding sites. Both in soleus muscle and the epididymal fat pad of the rat, there was a linear correlation between 42K influx and the initial rate of [3H]ouabain binding. The rate of ouabain binding is determined significantly by the rate of active Na-K transport, but within the time intervals studied (4-6 h) stimulation or inhibition of the Na pump does not lead to any appreciable change in the total number of Na pumps. It seems unlikely that the stimulation of active Na-K transport by insulin or adrenaline is due to unmasking or de novo synthesis of Na pumps.