EFFECTS OF Na+ AND OTHER MONOVALENT CATIONS ON Ca-EFFLUX FROM SYNAPTOSOMES

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Abstract
Effects of monovalent cations on Ca2+-efflux were examined in rat brain cortex slices, synaptosomes and synaptic plasma membranes. Effluxes of 45Ca2+ from brain slices and synaptosomes were stimulated by Na+ in medium, and the effects of Na+ on the 45Ca2+-effluxes disappeared at low temperature. Rb+ had more effect than Na+ on 45Ca2+-efflux from the synaptosomes, while Li+ had less effect. Release of Ca2+ from the synaptic plasma membranes preincubated with ATP, Mg2+, and 45Ca2+ was stimulated by Na+ and Li+. Cs+ and Rb+ were less effective on the release. There apparently is Na+-dependent Ca2+-efflux at nerve endings. The assumption that ATP-dependent Ca2+-binding with synaptic plasma membranes may be a partial reaction of Ca2+-efflux was not supported by these experiments.