Effect of taurine on calcium binding to microsomes isolated from rat cerebral cortex

Effects of taurine on Ca⁺⁺ binding to microsomes isolated from rat cerebral cortex were investigated in a medium containing various concentrations of KCl and/or NaCl. Calcium binding to microsomes was inhibited in a dose-dependent fashion by taurine in the incubation medium containing 5 mM KCl and 115 mM NaCl, while there was no inhibition in the medium containing 115 mM KCl and 5 mM NaCl. Taurine also decreased Ca⁺⁺ binding in the medium containing 70 mM KCl without NaCl. A similar tendency toward inhibition of the Ca⁺⁺ binding was observed in the medium with 5 mM or 120 mM KCl without NaCl. Taurine did not influence the Ca⁺⁺ binding in the medium containing different concentrations of NaCl without KCl, or in the medium from which KCl and NaCl were omitted. Isethionate, glycine, γ-aminobutyric acid, β-alanine and L-leucine did not significantly alter the Ca⁺⁺ binding to microsomes in the medium containing 70 mM KCl without NaCl. Thus it would appear that taurine may modulate the binding of calcium to microsomes in conditions which resemble the state of depolarization, while it is inactive in the normal resting state. This effect is apparently specific to taurine amongst a series of putative “inhibitory” amino acids.