title: Kinetics of bidirectional active sodium fluxes in the toad bladder.
abstract: The kinetics of isotopic Na+ flows was studied in urinary bladders of toads from the Dominican Republic. Initial studies of the potential dependence of passive serosal to mucosal 22Na+ efflux demonstrated the absence of isotope interaction and/or other coupling with passive Na+ flow. The electrical current I and mucosal to serosal 22Na+ influx were then measured with transmembrane potential clamped at deltapsi=0, 25, 50, 75 or 100 mV. Subsequent elimination of active Na+ transport with mucosal amiloride permitted calculation of the rates of active Na+ transport JaNa and active and passive influx leads to JaNa and leads to JpNa. The results indicate that for Dominican toad bladders mounted in chambers only Na+ contributes significantly to transepithelial active ion transport; hence JaNa=Ja. Ja was abolished at deltapsi=E=96.3+/-1.9 (S.E.) mV. As deltapsi approached E, active efflux comes from Ja became demonstrable. At deltapsi=100 mV, comes from Ja exceeded leads to Ja, so that Ja was negative. Experimental values of leads to Ja agreed well with theoretical values predicted by a thermodynamic formulation: leads to Jaexp=0.985 leads to Jatheor (r=0.993). The dependence of leads to Ja on deltapsi is curvilinear.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002024:Bufo marinus; D005260:Female; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008954:Models, Biological; D012964:Sodium / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism* / Q000502:physiology
chemical_list: D000584:Amiloride; D012964:Sodium