Insulin enhances sodium sensitivity of Na-K-ATPase in isolated rat proximal convoluted tubule
Féraille, E.; Carranza, M.L.; Rousselot, M.; Favre, H.
American Journal of Physiology 267(1 Pt 2): F55-F62
1994
ISSN/ISBN: 0002-9513 PMID: 8048565 Document Number: 437487
Insulin has been shown to stimulate the rate of ouabain-sensitive 86Rb influx in the isolated rat proximal convoluted tubule (PCT). To study the mechanism of this activation of Na-K-adenosinetriphosphatase (Na-K-ATPase), we determined the actions of insulin on 1) the maximal activity (V-max) of Na-K-ATPase hydrolytic activity; 2) the maximal rate of ouabain-sensitive 86Rb influx (after intracellular Na loading); 3) the rate of ouabain-sensitive 86Rb influx under conditions where intracellular Na concentration is rate limiting, either in the presence or in the absence of 5 times 10-4 M amiloride and/or low extracellular Na concentration (3 mM); and 4) the Na sensitivity of the Na-K-ATPase hydrolytic activity. The maximal rates of Na-K-ATPase hydrolytic activity and of ouabain-sensitive 86Rb uptake were unchanged by insulin. In contrast, we confirmed that insulin enhanced 86Rb uptake (in peq cntdot mm-1 cntdot min-1) in the absence of inhibitor of the Na/H exchanger (18.2 +- 1.7 to 24.1 +- 1.3 (SE), P lt 0.03) and, in addition, demonstrated a similar stimulation in the presence of either 5 times 10-4 M amiloride (7.2 +- 0.6 to 10.7 +- 0.9, P lt 0.01), 3 mM extracellular Na (4.1 +- 0.4 to 5.6 +- 0.2, P lt 0.05), and both amiloride and 3 mM extracellular Na (2.1 +- 0.7 to 4.5 +- 0.4, P lt 0.03). Finally, insulin increased the sensitivity of Na-K-ATPase to Na as the apparent dissociation constant decreased from 46.5 +- 5.3 to 27.6 +- 3.0 mM (P lt 0.03). These results suggest that, in isolated rat PCT, insulin stimulates the Na-K-ATPase without changing its V-max. by enhancing the Na sensitivity of the enzyme and thereby by increasing the pumping efficiency of each pump unit.