We used 31P NMR to investigate the temperature-dependence of intracellular pH (pH i ) in isolated frog skeletal muscles. We found that ln[H+ i ] is a linear function of 1/T abs paralleling those of neutral water (i.e., H+= OH−) and of a solution containing the fixed pH buffers of frog muscle cytosol. This classical van't Hoff relationship was unaffected by inhibition of glycolysis and was not dependent upon the pH or [Na+] in the bathing solution. Insulin stimulation of Na+-H+ exchange shifted the intercept in the alkaline direction but had no effect on the slope. Acid loading followed by washout resulted in an amiloride-sensitive return to the (temperature dependent) basal pH i .
These results show that the temperature dependence of activation of Na+-H+ exchange is similar to that of the intracellular buffers, and suggest that constancy of [H+]/[OH−] with changing temperature is achieved in the short term by intracellular buffering and in the long term by the set-point of the Na+-H+ exchanger. Proton activation of the exchanger has an apparent standard enthalpy change (ΔH°) under both control and insulin-stimulated conditions that is similar to the ΔH° of the intracellular buffers and approximately half of the ΔH° for the dissociation of water. Thus, the temperature-dependent component of the standard free-energy change (ΔF°) is unaffected by insulin stimulation, suggesting that changes in Arrhenius activation energy (E a ) may not be a part of the mechanism of hormone stimulation.
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Received: 12 February 1997/Revised: 1 October 1997
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Marjanovic, M., Elliott, A. & Dawson, M. The Temperature Dependence of Intracellular pH in Isolated Frog Skeletal Muscle: Lessons Concerning the Na+-H+ Exchanger. J. Membrane Biol. 161, 215–225 (1998). https://doi.org/10.1007/s002329900328