Effects of Taurine on Calcium Ion Uptake and Protein Phosphorylation in Rat Retinal Membrane Preparations

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Abstract
The effects of taurine on ATP-dependent Ca ion uptake and protein phosphorylation of rat retinal membrane preparations were investigated. Taurine (20 mM) stimulates ATP-dependent Ca ion uptake by 2-fold in crude retinal homogenates. It inhibits the phosphorylation of specific membrane proteins as shown by acrylamide gel electrophoresis and autoradiography. The close structural analog of taurine, 2-aminoethylhydrogen sulfate, demonstrates similar effects in both systems, i.e., stimulation of ATP-dependent Ca ion uptake and inhibition of protein phosphorylation; isethionic acid and guanidinoethanesulfonate have no effect on either system. A P1 subcellular fraction of the retinal membrane preparation that contains photoreceptor cell synaptosomes has a higher specific activity for the uptake of Ca ions. Phosphorylation of specific proteins in the P1 fraction is also inhibited by the addition of 20 mM taurine. Taurine has no effect on retinal ATPase activities or on phosphatase activity, thus, suggesting that it directly affects a kinase system.