title: Effects of electrochemical gradients on active sodium transport in toad urinary bladder.
abstract: To determine the concentration dependence of active sodium transport in toad urinary bladder, bidirectional fluxes of sodium were measured at three mucosal sodium concentrations (Cm) (114, 27, and 3 mM), before and after addition of sufficient ouabain to eliminate active transport. The results permit estimation of E, the electromotive force of the sodium pump, and its conductance, ga. E averaged 137 mV and was unaffected by depolarization or by reduction of Cm; ga fell by only 40%, suggesting that a Cm of 3 mM was still above the half-maximal value for the sodium pump. However, net open-circuit transport was estimated to become zero at Cm = 6 mM, owing to backflux through the shunt path, which did not vary with Cm. The flux ratio in the active path exhibited the type of abnormality first described as "single-file pore diffusion," which is attributed to relatively tight coupling between transport and metabolism.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002024:Bufo marinus / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D008433:Mathematics; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D001743:Urinary Bladder / Q000378:metabolism*
chemical_list: D010042:Ouabain; D012964:Sodium