Coupling of the Free Energy of Hydrolysis of ATP to Na+ Transport Across Frog Skin
Much is known separately about transepithelial Na+ transport and the ATP hydrolysis supporting that transport. However, relatively little is known concerning the coupling of the two processes, and much of that information has been derived from erythrocytes (Civan 1983). To examine this issue, a series of nuclear magnetic resonance (NMR) spectroscopic, electrophysiologic, and chemical analyses of frog skin have been initiated. In these studies, we have been concerned with two problems. First, we have wished to develop techniques to monitor the intracellular contents of Na+, ATP, phosphocreatine (PCr), and inorganic phosphate (Pi) noninvasively at room temperature. Second, we have compared the free energy of hydrolysis of intracellular ATP (- ΔG ATP c ) with the free energy expended by the Na,K-exchange pump (ΔG Na,K bl ) in extruding three sodium ions and accumulating two potassium ions. The results reviewed below indicate that the Na,K-exchange pump operates far from equilibrium and that (- ΔG ATP c ) is little affected by large changes in Na+ transport across frog skin.
KeywordsNuclear Magnetic Resonance Nuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance Analysis Frog Skin Frog Skeletal Muscle
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