[Alteration of frog in vitro electroretinographic c-wave in modified extracellular cation concentration]

Effects of extracellular cation (Ca2+, Mg2+, Na+) concentrations on the electroretinographic c-wave were studied in the isolated neural retina-retinal pigment epithelium-choroid tissue of the bullfrog. Among the conditions studied (Ca2+, 0.5-5.0 mM: Mg2+, 0.5-5.0 mM: Na2+, 89.0-109.0 mM), only Ca2+ concentration significantly affected the c-wave. Between 1.0 mM and 5.0 mM Ca2+, the amplitude and the rise time (interval from the light onset to 90% amplitude) of the c-wave were positively and reversely correlated to Ca2+ concentration, respectively. The present results suggest that Ca2+ is one of the major determinants in the extracellular milieu on the c-wave, which is presumably due to its effects on the photoreceptoral activities.