Modulation of the membrane potential of the Schwann cell of the squid giant nerve fiber.

1. The involvement of second messengers and of other chemical mediators, in the modulation of the membrane potential of the Schwann cell of the giant nerve fiber of the Tropical squid Sepioteuthis sepioidea is described. 2. The involvement of the cyclic nucleotide adenosine 3', 5' monophosphate (cAMP) in mediating the actions of the nicotinic Ach receptors of the Schwann cells is suggested. 3. The presence of octopaminergic receptors in the Schwann cells, mediating their actions through the activation of adenylate cyclase, is also described. 3. Receptors for vasoactive intestinal peptide (VIP) are also present on the Schwann cells, and their actions are mediated via a second messenger system that does not involve the activation of adenylate cyclase. 5. The three independent receptor systems referred above are able to interact in a complex way, which involves both their direct actions on the Schwann cell membrane potential and modulatory effects between the systems.