Neuronal nicotinic acetylcholine receptors of ganglion cells in the cat retina.
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 microns, 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 x 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 x 10(-6) M. The muscarinic antagonist, atropine, showed a concentration-dependent reduction in the amplitude of IACh with an IC50 of 4.4 x 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.
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