Insulin enhances sodium sensitivity of Na-K-ATPase in isolated rat proximal convoluted tubule.
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 (Vmax) 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 x 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.mm-1.min-1) in the absence of inhibitor of the Na/H exchanger [18.2 +/- 1.7 to 24.1 +/- 1.3 (SE), P < 0.03] and, in addition, demonstrated a similar stimulation in the presence of either 5 x 10(-4) M amiloride (7.2 +/- 0.6 to 10.7 +/- 0.9, P < 0.01), 3 mM extracellular Na (4.1 +/- 0.4 to 5.6 +/- 0.2, P < 0.05), and both amiloride and 3 mM extracellular Na (2.1 +/- 0.7 to 4.5 +/- 0.4, P < 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 < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
Féraille
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Division de Néphrologie, Hôpital Cantonal Universitaire, Geneva, Switzerland.
Carranza
M L
ML
Rousselot
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M
Favre
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H
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D005110:Extracellular Space / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D010539:Permeability; D051381:Rats; D017208:Rats, Wistar; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007328:Insulin; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium