The role of cyclic nucleotides in modulation of the membrane potential of the Schwann cell of squid giant nerve fibre.

The role of cyclic nucleotides in mediating the effects of nicotine cholinergic receptors has been investigated in Schwann cells of the giant nerve fibre of the squid. Elevation of cyclic AMP levels in this preparation by means of the phosphodiesterase inhibitor, theophylline, by the diterpene adenylate cyclase activator, forskolin, and by cyclic nucleotide analogues mimics the action of activating the nicotinic cholinergic receptors in producing a long-lasting hyperpolarization of the membrane potential of the Schwann cell. Theophylline and forskolin also potentiate the effects of carbachol and of neural stimulation on the Schwann cell. The results suggest that the nicotinic receptor of the squid Schwann cell is likely to mediate its effects via a mechanism that activates adenylate cyclase. The results are discussed in terms of the role of cyclic AMP in the complex multistep interaction between the giant axon of the squid and its surrounding Schwann-cell layer.