Roles for arachidonic acid and GTP-binding proteins in synaptic transmission

Using synapses which form between somata of Helisoma neurons in cell culture we have studied the presynaptic regulation of synaptic transmission. GTP-binding proteins play important roles in regulating synaptic transmission through their actions on calcium currents, potassium currents and secretory apparatus. Heterotrimeric G proteins continuously regulate the amount of transmitter released at the synapse. By interacting with the arachidonic acid second messenger system they modulate potassium channels, and could potentially control the secretory apparatus. Perturbations of the rab protein system did not affect action potential-evoked transmission, but did control the frequency of miniature inhibitory postsynaptic currents. This is consistent with the involvement of this type of GTP-binding protein in the control of secretory apparatus, but suggests that rab proteins are not used to regulate the amount of transmitter released at the synapse. Using the Helisoma cellular system which permits direct access to the presynaptic site of transmitter release we are going on to study further the role of arachidonic acid, Go, Gi and rab proteins on the regulation of the secretory apparatus.