ABSTRACT
Gap junction channels mediate cell-to-cell diffusion of small cytoplasmic molecules, enabling cells to communicate directly with each other cell coupling. In several cells, evidence for the participation of a calmodulin (CaM)-like intermediate of channel gating has been produced. The CaM hypothesis for coupling regulation is based on the capacity of CaM inhibitors to prevent cell uncoupling in amphibian embryos and in crayfish septate axons. Cytoplasmic acidification has shown to affect intracellular calcium (Ca++) in various other cells. Ca++ was found to increase with lowered pH in squid giant axons, in molluscan neurons, and in Xenopus embryonal cells. The chapter reviews the relationship between gap junction channel permeability and Ca++ or hydrogen (H+) concentration. It discusses on the basis of experimental data obtained in crayfish septate axons where junctional electrical resistance and either Ca++ or H+, were measured during uncoupling induced by acidification. Ryanodine inhibits the effect of acidification by blocking the Ca++ release channels of either reticulum or calciosomes.
