Effects of ATP and taurine on calcium uptake by membrane preparations of the rat retina.

The effects of ATP and taurine on the kinetics of calcium uptake in rat retinal membrane preparations were determined. ATP increased calcium uptake at low calcium ion concentrations. Addition of ATP plus taurine further increased calcium uptake. Cooperative relationships were observed for calcium uptake in the absence of ATP and taurine. In the presence of phosphate ions reciprocal plots demonstrated upward deflections from linearity, while in the absence of phosphate ions downward deflections were noted. Addition of ATP plus taurine to the incubation system appeared to obliterate the cooperativity. Two uptake systems for calcium were observed.