Effects of semi-starvation and potassium deficiency on the concentration of [3H]ouabain-binding sites and sodium and potassium contents in rat skeletal muscle

1. Using vanadate-facilitated [³H]ouabain binding, the effect of semi-starvation on the total concentration of [³H]ouabain-binding sites was determined in samples of rat skeletal muscle. When 12-week-old rats were semi-starved for 1, 2 or 3 weeks on one-third to half the normal daily energy intake, the [³H]ouabain-binding site concentration in soleus muscle was reduced by 19, 24 and 25% respectively. In extensor digitorum longus, diaphragm and gastrocnemius muscles the decrease after 2 weeks of semi-starvation was 15, 18 and 17% respectively. The decrease was fully reversible within 3d of free access to the diet. Complete deprivation of food for 5d caused a reduction of 25% in soleus muscle [³H]ouabain-binding-site concentration. It was excluded that the reduction in [³H]ouabain binding was due to a reduced affinity of the binding site for [³H]ouabain. 2. Semi-starvation of 12-week-old rats for 3 weeks caused a reduction of 45 and 53% in 3, 5, 3'triiodothyronine (T₃) and thyroxine (T₄) levels respectively. As reduced thyroid hormone levels have previously been found to decrease [³H]ouabain-binding-site concentration in skeletal muscle, this points to the importance of T₃and T₄in the down-regulation of the [³H]ouabain-binding-site concentration in skeletal muscle with semi-starvation. Whereas potassium depletion caused a decrease in K content as well as in [³H]ouabain-binding-site concentration in skeletal muscles, semi-starvation caused only a tendency to a decrease in K content. Thus, K depletion is not a major cause of the reduction in [³H]ouabain-binding-site concentration with semi-starvation. 3. Due to its high concentration of Na, K pumps, skeletal muscle has a considerable capacity for clearing K from the plasma as well as for the binding of digitalis glycosides. Semi-starvation causes a severe reduction in the total skeletal muscle pool of Na, K pumps and may therefore be associated with impairment of K tolerance and increased digitalis toxicity.