Phospholipidcholesterol membrane model. Control of resistance by ions or current flow.

A cephalin-cholesterol membrane model is described whose electrical resistance can be reversibly raised by CaCl(2) or lowered by KCl or NaCl whether these ions are added to the membrane by mechanical immersion or are driven in electrically. Either KCl or NaCl acts antagonistically to CaCl(2). Experiments with controlled pH indicate that the above effects depend somehow on combination of the cations with the phospholipid acidic groups. Also, they are correlated with decreased membrane hydration in CaCl(2) solutions, and increased hydration in KCl or NaCl solutions. It is conjectured that cells may regulate their transsurface ion pathways and fluxes by K-Ca competition for negatively charged binding sites on plasma membrane phospholipid. It is regarded as a corollary to say that a fundamental event in excitation is displacement of membrane Ca from such a site by catelectrotonically propelled K.