Cooperative interaction among cell surface sites: evidence in support of the surface adsorption theory of cellular...

Resting potentials were studied in frog sartorius muscles equilibrated in Ringer solutions that contained various concentrations of K+. Cells in solutions that contained near-zero K+ showed a rise in potential followed by a slow decline over about 70 hours that paralleled the loss of cellular K+ in exchange for Na+. When these cells were placed in 2.5 mM K+, the re-gain of the potential occurred much more rapidly than the re-gain of cellular K+. Thus, there was no consistent relation between resting potential and concentration of intracellular K+. When cells were immersed in solutions containing 100 mM Na+ and K+ at concentrations of 2.5 mM and greater, there was a semi-logarithmic relation between potential and [K+]ex, in which potential declined as [K+]ex increased. However, when cells were equilibrated in [K+]ex below 2.5 mM, the potential peaked and then declined as [K+]ex decreased. The results are readily explained by the surface adsorption model of the cellular potential, in which the potential is determined simply by the nature of the fixed surface charges that interact with one another in a cooperative manner. The peak and decline of the potential with decreasing [K+]ex below 2.5 mM mirrors the autocooperative shift in the affinity of the surface charged sites from one that favors K+ over Na+ strongly to one that favors K+ over Na+ less strongly.