Properties of neuronal type acetylcholine receptors in voltage clamped mouse neuroblastoma cells.

The pharmacological and physiological characteristics of nicotinic acetylcholine receptor-mediated ion current in mouse neuroblastoma N1E-115 cells have been investigated by superfusion of voltage clamped cells with known concentrations of agonists and antagonists for short periods. The acetylcholine-induced inward current is blocked by d-tubocurarine and by kappa-bungarotoxin with IC50 values of 0.5 microM and 30 nM, respectively. The inward current is resistant to alpha-bungarotoxin up to a concentration of 0.5 microM. This allows classification of the acetylcholine receptors of N1E-115 cells as neuronal type nicotinic receptors. The amplitude of the inward current increases with increasing concentration of the agonists acetylcholine and carbamylcholine, resulting in concentration-effect curves with EC50 values of 53 and 240 microM and slope factors slightly below unity. Conversely, at the highest concentrations of the agonists the amplitude of the inward current is reduced and a transient increase of the current appears when the agonist is removed. The characteristics of this transient tail current indicate that the agonists cause rapid ion channel block by interacting with a low affinity site. In the continued presence of acetylcholine the peak inward current is reduced by desensitization. The IC50 value and the slope factor of the steady-state desensitization curve are 1.1 microM and 0.58, respectively. At a low concentration of acetylcholine both the onset of desensitization and the inward current decay are described by similar dual exponential kinetics, but the steady-state inward current is smaller than expected from the degree of desensitization. Neuronal nicotinic receptors in N1E-115 cells and end-plate nicotinic receptors have several characteristics in common. However, the present results indicate that these receptors are distinct, not only in their sensitivity to snake toxins, but also with respect to functional properties.