Sodium transport and oxygen consumption in toad bladder: A thermodynamic approach |
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Authors: | Michael A Lang SRoy Caplan A Essig |
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Institution: | 1. Department of Physiology, Boston University School of Medicine, Boston, Mass. 02118 U.S.A.;2. Laboratory of Membranes and Bioregulation, Weizmann Institute of Science, Rehovot Israel |
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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+/O2 was constant for each tissue, but varied among different tissues. Only when Δψ was varied did the ratio Na+/dO2 change with the rate of active sodium transport; under these circumstances dNa+/dO2 was constant but exceeded the ratio measured at short-circuit (Na+/O2)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. |
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