A simple electrostatic model can explain the effect of pH upon the force-pCa relation of skinned frog skeletal muscle fibers

Biophysical Journal
R E Godt

Abstract

The relative force-pCa relation of skinned frog skeletal muscle fibers is shifted along the pCa axis by changes in pH. This shift has been interpreted as arising from competition between H+ and Ca2+ for a binding site on troponin. Unfortunately, binding studies have been unable to confirm such competition. Alternatively, however, the data fit a model where H+ influences the degree of dissociation of ionizable groups on the surface of the thin filaments, thus altering the electrostatic potential surrounding the filaments. Alterations in the potential will, in turn, change the concentration of Ca2+ near the troponin binding sites in accordance with the Boltzmann relation. A simple model, based upon the Gouy-Chapman relation between surface potential and charge density, provides a quantitative explanation for the shift of the relative force-pCa curve with pH, given a reasonable estimate of the surface charge density on the thin filament. A best fit is obtained when the ionizable groups giving rise to the potential have a log proton ionization constant (pKa) of 6.1, similar to that for the imidazole group on histidine, and when the density of these groups is near that estimated from amino acid analysis of thin filament proteins and...Continue Reading

Citations

Nov 1, 1994·Acta Physiologica Scandinavica·G S LynchD A Williams
Feb 14, 2002·Journal of Applied Physiology·Dilson E Rassier, Walter Herzog
Jun 1, 1990·The American Journal of Physiology·C H Orchard, J C Kentish

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