Sodium transport and oxygen consumption in toad bladder: A thermodynamic approach

Abstract

The relationship between active sodium transport and oxygen consumption was investigated in toad urinary bladder exposed to identical sodium-Ringer's solution at each surface, while controlling the transepithelial electrical potential difference Δψ. Rates of sodium transport and oxygen consumption were measured simultaneously, both in the short-circuited state ( Δψ = 0) and when Δψ was varied. Under short-circuit conditions, when the rates of active sodium transport changed spontaneously or were depressed with amiloride, the ratio of active sodium transport to the estimated suprabasal oxygen consumption Na +/O 2 was constant for each tissue, but varied among different tissues. Only when Δψ was varied did the ratio Na +/dO 2 change with the rate of active sodium transport; under these circumstances dNa +/dO 2 was constant but exceeded the ratio measured at short-circuit [(Na +/O 2) Δψ=0]. This suggests that coupling between transport and metabolism is incomplete. The results are analyzed according to the principles of nonequilibrium thermodynamics, and interpreted in terms of a simple model of the transepithelial sodium transport system.