Effect of insulin on Na+,K(+)-ATPase in rat collecting duct.
AUTOR(ES)
Féraille, E
RESUMO
1. The collecting duct is involved in the whole antinatriuretic effect of insulin, as indicated in vitro by the stimulatory effect of the hormone on ouabain-sensitive 86Rb+ uptake. Since Na+,K(+)-ATPase drives Na+ reabsorption, the contribution of the Na+ pump to the effect of insulin was investigated in rat isolated cortical and outer medullary collecting duct. 2. Insulin enhanced ouabain-sensitive 86Rb+ uptake in the absence, as well as in the presence, of either 5 x 10(-4) M amiloride or 10(-3) M hydrochlorothiazide (HCT). Maximal ouabain-sensitive 86Rb+ uptake, measured in Na(+)-loaded tubules, was also enhanced by insulin. The insulin effect persisted both in the absence of external Na+, when the Na+,K(+)-ATPase operates in a Rb(+)-Rb+ exchange mode, and in tubules depolarized by a high external concentration (20 mM) of Rb+ or by addition of 3 mM Ba2+. 3. Insulin treatment did not alter the intracellular Na and K concentrations, the specific binding of [3H]ouabain measured in intact tubules, or the hydrolytic activity of Na+,K(+)-ATPase measured after permeabilization of the tubule cells. 4. In conclusion, in the rat collecting duct, insulin increased Na+,K(+)-ATPase-mediated cation transport independently of Na+ availability, membrane potential and recruitment of pump units. The effect of insulin was lost after cell permeabilization, suggesting the presence of a cytosolic factor which controls the turnover of Na+,K(+)-ATPase.
ACESSO AO ARTIGO
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