Stoichiometry and coupling of active transport to oxidative metabolism in epithelial tissues.

A linear relationship has been observed between the rate of active ion transport and the oxygen consumption or lactate production rate in a variety of epithelia. Stoichiometries of ions transported per oxygen consumed or ATP utilized calculated from these relationships reflect actual properties of the active transport step when the following two conditions are met: 1) the basal metabolic rate, obtained in the absence of active transport, remains constant at all rates of active transport; and 2) all the net transport across the tissue considered in the calculation traverses through active (energy-dissipative) pathways. The nature of the cellular mechanism linking active transport and energy production is a fundamental physiological question. Experimental alterations in the rate of active transport elicit mitochondrial state transitions and/or changes in adenine nucleotide concentrations in various epithelia. These findings, obtained by optical and biochemical methods, indicate that ATP and its hydrolysis products constitute part of the coupling mechanism linking the turnover of transport ATPase and the aerobic metabolic rate in epithelia.