Voltage-dependent effect of tetraethylammonium on the nicotinic acetylcholine receptors of rat superior cervical ganglion neurons

The effect of tetraethylammonium (TEA) on the currents evoked in neurons of the rat superior cervical ganglion by iontophoretic application of acetylcholine (ACh) was studied using a whole-cell patch-clamp recording technique. Tetraethylammonium was used at a concentration of about 20 mu M, providing no blocking effect on the ACh-induced membrane currents at a range of positive membrane potentials and reducing these currents recorded at a range of negative membrane potentials by about half. The blocking effect of TEA increased with hyperpolarization within the -50 to -90 mV membrane potential range, and did not depend on the membrane potential level within a range of 0 to -50 mV. The analysis of dose dependence showed that both the voltage-dependent and the voltage-independent blocking effects are due to TEA competitive action on the ganglionic nicotinic acetylcholine receptors (nAChR). The results suggest that the TEA-induced competitive blockade is voltage-dependent.