Abstract
The effects of eserine and D-tubocurarine on the axon and Schwann cell membrane potentials have been studied in the giant nerve fibre of the squid.1. The addition of eserine at concentrations of up to 10(-4)M to the external sea-water medium has no appreciable effects on either the Schwann cell electrical potential of unstimulated nerve fibres or on the resting and action potentials of the axon.2. However, eserine at a concentration of 10(-9)M prolongs the long-lasting Schwann cell hyperpolarizations which follow the conduction of impulse trains by the axon.3. Higher concentrations of eserine (10(-7), 10(-4)M) decrease and block the long-lasting effects of nerve impulse train conduction.4. D-tubocurarine at concentrations of up to 10(-5)M has no appreciable effect on the resting and action potentials of the axon.5. However, D-tubocurarine at a concentration of 10(-9)M blocks completely the hyperpolarizing effects of nerve impulse trains on the Schwann cell electrical potential.6. In addition to its blocking action, D-tubocurarine induces transient hyperpolarizations in the Schwann cells of unstimulated nerve fibres both in intact fibres and in slitted preparations.7. These findings suggest that a cholinergic system, which may be located at the axon-Schwann cell boundary, is involved in the genesis of the long-lasting Schwann cell hyperpolarization caused by the conduction of nerve impulse trains by the axon.