Acetylcholine-activated currents in mouse neuroblastoma cells

Aluminium modifies the electrical response of neuroblastoma cells to a short hypertonic pulse

The effect of aluminium (50-100 micrograms/ml) on the electrical response of N1E-115 neuroblastoma cells to a short hypertonic pulse was examined using conventional electrophysiological techniques and computer assisted analysis. Application of a small dose of hypertonic solution in the vicinity of the cell evoked depolarization of the membrane potential and a biphasic change in input resistance: an initial increase followed by a profound decrease. Upon washout of the hypertonic stimulus, repolarization of membrane potential and complete recovery of the input resistance were observed. In the presence of aluminium application of hypertonic solution had a reversible effect which showed a prolonged duration of the response without a change in its amplitude. It is suggested that the retardation in recovery from hypertonically induced shock may be due to rigidification of the plasma membrane in the presence of aluminium. Possible implications to human diseases associated with accumulation of aluminium in brain tissue are discussed.

Single-channel currents of rat neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes

The neuronal nicotinic acetylcholine receptor subunits alpha 2, alpha 3, and alpha 4 form functional receptors with the beta 2 subunit. Each of these subunit combinations shows two distinct open states (referred to as primary and secondary). The primary open states of alpha 2 beta 2, alpha 3 beta 2, and alpha 4 beta 2 receptors were 33.6 +/- 1.8 pS, 15.4 +/- 0.8 pS, and 13.3 +/- 1.5 pS, respectively. The open times of the alpha 3 beta 2 primary open state were significantly longer than the open times of the other primary conductance states. The secondary open states of alpha 2 beta 2 and alpha 3 beta 2 were 15.5 +/- 1.3 pS and 5.1 +/- 0.4 pS, respectively. Secondary open states were seen infrequently with alpha 4 beta 2. Oocytes injected with alpha 2 RNA and a 9-fold excess of beta 2 RNA showed an enhanced expression of the secondary open state.

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.