Diamide stimulates calcium-sodium exchange in dog red blood cells

Calcium influx can be stimulated in dog red blood cells by preexposure to diamide under certain conditions. Diamide-activated calcium influx resembles swelling-induced Ca2+-Na+ exchange in several respects. These include saturation of calcium influx at external calcium levels greater than 0.5 mM, suppression of calcium influx by external sodium, and inhibition by quinidine. The ability of diamide to stimulate this transport pathway depends critically on the ionic composition of the medium in which the cells are bathed at the time of diamide exposure. The effect is greatest if the diamide preincubation is conducted in a hypotonic lithium chloride medium containing at least 1 microM calcium. Stimulation of Ca2+-Na+ exchange is seen at diamide concentrations (0.10-0.33 mM) that are lower than those reported to cause major spectrin cross-linking, glutathione depletion, Ca2+-ATPase inhibition, or ion channel formation. The results suggest that dog red cells have a large latent capacity for Ca2+-Na+ exchange.