The Temperature Dependence of Intracellular pH in Isolated Frog Skeletal Muscle: Lessons Concerning the Na+-H+ Exchanger |
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Authors: | M Marjanovic AC Elliott MJ Dawson |
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Institution: | (1) Department of Molecular & Integrative Physiology, 524 Burrill Hall, 407 S. Goodwin Ave, Urbana, IL 61801, USA, US |
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Abstract: | We used 31P NMR to investigate the temperature-dependence of intracellular pH (pH
i
) in isolated frog skeletal muscles. We found that lnH+
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.
Received: 12 February 1997/Revised: 1 October 1997 |
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Keywords: | :31P NMR spectroscopy — Frog muscle — pHi regulation — Na+-H+ exchange — Temperature — Enthalpy |
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