Regulation of Neurotransmitter Release by a Complex of Actin with Relaxing Protein Isolated from Rat Brain Synaptosomes

An actin-relaxing protein complex was isolated from rat brain synaptosomal membranes by attachment to muscle myosin bound by the surface of polystyrene (Lytron) particles.These particles acquired Mg2+ATPase activity.The brain actin-relaxing protein complex, dissociated from muscle myosin-Lytron complex by ATP, reacted with synaptic vesicles "preloaded" with 'Cglutamate mediating the release of labeled glutamate and activation of Mg2+ATPase.Both release of l*C and ATPase activity were inhibited by ethylene glycol bis(&aminoethyl ether)-N, N'-tetraacetic acid (EGTA) and stimulated by addition of 0.4 mM Ca2+.Isolated brain actin-relaxing protein complex conferred Ca2+ sensitivity to muscle myosin in the presence of EGTA.Stimulation of Mg2+ATPase activity and Wglutamate release from synaptic vesicles was also generated by a complex of muscle Factin-relaxing protein.The data suggest that contractile proteins are important in mediation of the release of neurotransmitters in brain tissue.