Characterization of acetylcholine receptors in the Schwann cell membrane of the squid nerve fibre.

1. The effects of alpha-bungarotoxin, nicotine and muscarine on the Schwann cell membrane potential have been studied in the giant nerve fibre of the squid. The external application of alpha-bungarotoxin (10(-6), 10(-8), 10(-9) M) irreversibly blocks the long-lasting Schwann cell hyperpolarizations following the conduction of nerve impulse trains by the axon. It also blocks the Schwann cell hyperpolarizing response to the external application of carbamylcholine (10(-6)M) to the resting nerve fibre. 2. Externally applied D-tubocurarine (10(-5)M) protects against the irreversible action of alpha-bungarotoxin (10(-9)M) on the Schwann cell. Within 10 min of reimmersion in toxin-free sea water there is complete recovery of the Schwann cell hyperpolarizing response to carbamylcholine (10(-6)M) which had been initially abolished. 3. Nicotine (10(-6)M) induces a prolonged hyperpolarization of the Schwann cells in the resting nerve fibre, wheras at the same concentration, muscarine has no appreciable effect on the Schwann cell membrane potential. 4. None of these drugs, at the concnetrations utilized in the present study, had any appreciable effect on the resting and action potentials of the axon. 5. These findings show the presence of acetylcholine receptors of the nicotinic type in the Schwann cell membrane, and give further support to the hypothesis on the role of the acetylcholine system in the genesis of the long-lasting Schwann cell hyperpolarizations caused by the conduction of nerve impulse trains by the axon.