MYOSIN-II IS INVOLVED IN TRANSMITTER RELEASE AT SYNAPSES FORMED BETWEEN RAT SYMPATHETIC NEURONS IN CULTURE

The presynaptic function of myosin II was studied at cholinergic synap ses formed between rat superior cervical ganglion neurons in culture. Immunofluorescent staining showed that myosin II was colocalized with synaptophysin at the presynaptic nerve terminals. Antimyosin II antibo dy introduced into presynaptic neurons inhibited synaptic transmission . Transmission was also inhibited in a dose-dependent manner by two in hibitors of myosin light chain kinase: a peptide, SM-1, and an organic inhibitor, wortmannin. The inhibition produced by these agents was de pendent on presynaptic activity. Extracellularly applied wortmannin al so blocked synaptic transmission, but its effects were slower in onset . Wortmannin also decreased postsynaptic potentials and post-tetanic p otentiation in intact superior cervical ganglia. These results suggest a model in which myosin light chain kinase phosphorylates myosin, and the resultant change in actin-myosin interactions is involved in neur otransmitter release.