Aldosterone and insulin effects on driving force of Na+ pump in toad bladder.
Both aldosterone and insulin increase active Na+ transport across the urinary bladder of the toad. Recent data have provided further support to the concept that aldosterone acts primarily to increase Na+ entry from the mucosal medium into the transporting cells, whereas insulin acts to increase active Na+ extrusion into the serosal medium. To examine this concept further, the driving force (E(Na)) of the Na+ pump was measured, by the technique described by Yonath and Civan (48), before and after hormonal administration. Both hormones increased short-circuit current, but only insulin increased E(Na). The validity of the technique was further explored by imposing periods of hypoxia upon a series of experimental hemibladders; as expected, hypoxia reversibly decreased E(Na). The data indicate that insulin stimulates Na+ transport, in part by directly stimulating the Na+ pump. The results are also consistent with the concept that aldosterone stimulates net Na+ movement solely by enhancing Na+ entry into the transporting cells, but are subject to alternative interpretations.
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002024:Bufo marinus; D004553:Electric Conductivity; D005260:Female; D000860:Hypoxia; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
D007328:Insulin; D000450:Aldosterone; D012964:Sodium