Dependence of the driving force of the sodium pump on rate of transport

Abstract

The driving force for active transport of Na⁺ in the isolated toad bladder, E_Na, was measured as the reciprocal slope of the change in conductance with change in short-circuit current after stimulation with antidiuretic hormone. The base-line short-circuit current was altered by change in ambient Na⁺ concentration or addition of amiloride, maneuvers which alter availability of Na⁺ at the site of active transport. In the absence of a chemical gradient for Na⁺ across the bladder, E_Na was found to be inversely related to the rate of Na⁺ transport, a finding incompatible with the simple electrical analogue that has been proposed for the system. The results provide additional support for the view that E_Na measured in this way has both energetic and kinetic components. membrane transport; active transport; sodium transport; E_Na Submitted on April 23, 1976