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

The effects of La , Mn++ and ruthenium red (R.R.) on Ca-uptake of synaptic plasma membranes (S.P.M.) were investigated. La (0.1 mM), Mn++ (0.2 mM) and R.R. (0.1 mM) selectively inhibited Mg-Ca-ATPase but did not significantly affect Mg-ATPase activity. The apparent Ki values of La , Mn++ and R.R. for Mg-Ca-ATPase were 0.05, 0.06 and 0.03 mM, respectively. La , Mn++ and R.R. did not affect Ca-uptake at concentrations which strongly inhibited Mg-Ca-ATPase activity. These results indicate that Ca-uptake by S.P.M. differ from that by sarcoplasmic reticulum.