Neuronal Nicotinic Acetylcholine Receptors of Ganglion Cells in the Cat Retina

Abstract

Ganglion cells, retrogradely labeled with DiI, were dissociated from the cat retina. Under the whole-cell clamp mode using a patch pipette, ACh induced a transient current (IAch) in all cells tested. The soma diameter of ACh-responsive cells distributed from 11 to 23 μm, indicating that the preparation included Y, X, and W cells. IACh was inward rectifying. The reversal potential of IACh was close to the zero-current potential predicted from the intra- and extracellular monovalent cation concentrations by the Goldman-Hodgkin-Katz equation. The concentration-response curve gave a Hill coefficient of 0.89 and an EC50 of 3.2 × 10-5 M. Nicotine (10-4 M) induced a transient current, while muscarine (10-4 M) was ineffective. The nicotinic antagonist, hexamethonium, reduced the amplitude of IACh in a concentration-dependent manner with an IC50 of 1.3 × 10-6 M. The muscarinic antagonist, atropine, showed a concentration-dependent reduction in the amplitude of IACh with an IC50 of 4.4 × 10-6 M. The amplitude of IACh was dependent on the extracellular Ca2+ concentration ([Ca2+]o); small at low [Ca2+]o and large at high [Ca2+]o. The time course of desensitization was also dependent on [Ca2+]o; fast at low [Ca2+]o and slow at high [Ca2+]o. The replacement of extracellular Ca2+ to Sr2+ increased the amplitude of IACh, but replacement to other divalent cations reduced it. The results indicate the presence of functional neuronal nicotinic ACh receptors in Y, X, and W cells. © 1995, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.