EFFECTS OF La+++, Mn++ AND RUTHENIUM RED ON Mg.Ca-ATPase ACTIVITY AND ATP-DEPENDENT Ca-BINDING OF THE SYNAPTIC PLASMA MEMBRANE

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Abstract
The effects of La3+, Mn2+ and ruthenium red (RR) on Ca2+-uptake of [rat] synaptic plasma membranes (SPM) were investigated. La3+ (0.1 mM), Mn2+ (0.2 mM) and RR (0.1 mM) selectively inhibited Mg2+.cntdot.Ca2+-ATPase did but did not significantly affect Mg2+-ATPase activity. The apparent Ki values of La3+, Mn2+ and RR for Mg2+.cntdot.Ca2+-ATPase were 0.05, 0.06 and 0.03 mM, respectively. La3+, Mn2+ and RR did not affect Ca2+-uptake at concentrations which strongly inhibited Mg2+.cntdot.Ca2+-ATPase activity. Ca2+-uptake by SPM apparently differs from that by sarcoplasmic reticulum.