The mechanism of insulin stimulation of (Na+,K+)-ATPase transport activity in muscle.
Since the mechanism underlying the insulin stimulation of (Na+,K+)-ATPase transport activity observed in multiple tissues has remained undetermined, we have examined (Na+,K+)-ATPase transport activity (ouabain-sensitive 86Rb+ uptake) and Na+/H+ exchange transport (amiloride-sensitive 22Na+ influx) in differentiated BC3H-1 cultured myocytes as a model of insulin action in muscle. The active uptake of 86Rb+ was sensitive to physiological insulin concentrations (1 nM), yielding a maximum increase of 60% without any change in 86Rb+ permeability. In order to determine the mechanism of insulin stimulation of (Na+,K+)-ATPase activity, we demonstrated that insulin also stimulates passive 22Na+ influx by Na+/H+ exchange transport (maximal 200% increase) and an 80% increase in intracellular Na+ concentration with an identical time course and dose-response curve as insulin-stimulated (Na+,K+)-ATPase transport activity. Incubation of the cells with high [Na+] (195 mM) significantly potentiated insulin stimulation of ouabain-inhibitable 86Rb+ uptake. The ionophore monensin, which also promotes passive Na+ entry into BC3H-1 cells, mimics the insulin stimulation of ouabain-inhibitable 86Rb+ uptake. In contrast, incubation with amiloride or low [Na+] (10 mM), both of which inhibit Na+/H+ exchange transport, abolished the insulin stimulation of (Na+,K+)-ATPase transport activity. Furthermore, each of these insulin-stimulated transport activities displayed a similar sensitivity to amiloride. These results indicate that insulin stimulates a large increase in Na+/H+ exchange transport and that the resulting Na+ influx increases the intracellular Na+ concentration, thus activating the internal Na+ transport sites of the (Na+,K+)-ATPase. This Na+ influx is, therefore, the mediator of the insulin-induced stimulation of membrane (Na+,K+)-ATPase transport activity classically observed in muscle.
Rosić
N K
NK
Standaert
M L
ML
Pollet
R J
RJ
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D002352:Carrier Proteins; D007328:Insulin; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium