Combined effects of adrenaline and insulin on active electrogenic Na⁺–K⁺ transport in rat soleus muscle

Abstract

Both β₂-adrenoreceptor stimulants (such as adrenaline and salbutamol) and insulin can increase active Na⁺–K⁺ transport^1–6 and hyperpolarise skeletal muscle cells^1,2,7–9. Thus, adrenaline and insulin, which are otherwise antagonistic regulators of several metabolic processes, have one action in common, namely, stimulation of active ion translocation. This is especially interesting as cyclic AMP stimulates Na⁺–K⁺ transport², whereas a lowering of the cytoplasmic concentration of cyclic AMP has been proposed as an early signal in the action of insulin^10,11. Here we report the results of experiments in which the active Na⁺–K⁺ transport and membrane potential (E_M) of rat soleus muscles were studied during the action of supramaximal doses of insulin and β₂-adrenoreceptor stimulants, alone and in combination. We conclude that the stimulant action of insulin on active electrogenic Na⁺–K⁺ transport is unlikely to be evoked by a lowering of the intracellular concentration of cyclic AMP.