pH sensitivity of calmodulin distribution in nervous tissue fractions

Alkalinization of nervous system extracts of the mollusk, Pleurobranchaea, from pH 7.0 to 8.0 markedly increases the ratio of soluble to total calmodulin. This effect is independent of pH effects on free Ca2+ concentration and is pronounced at micromolar (near intracellular) levels of Ca2+. These data may relate to recent evidence that Ca2+/calmodulin-activated cyclic nucleotide phosphodiesterase mediates the effects of small changes in intracellular pH (0.1-0.2 units) on the electrical activity of neurons. Calmodulin redistribution could reflect altered availability to stimulate phosphodiesterase activity and supports a role for calmodulin in mediating effects of intracellular pH fluxes on cellular activity.