Endocrinology, Vol 130, 825-830, Copyright © 1992 by Endocrine Society

ARTICLES

Nerve growth factor enhances [3H]nicotine binding to a nicotinic cholinergic receptor on PC 12 cells

TC Madhok and BM Sharp
Department of Medicine, Hennepin County Medical Center, Minneapolis, Minnesota.

Although nicotinic cholinergic agonists have functional effects on PC 12 cells, radioligand-binding sites have not been detected. We, therefore, studied PC 12 cells incubated in the presence of nerve growth factor (NGF) and determined that specific [3H]nicotine-binding sites were induced approximately 2.5-fold in the presence of NGF (50 or 100 ng/ml). Specific binding was maximal between the first (100 ng/ml NGF) and seventh (50 ng/ml NGF) days of treatment and was stable for 2 weeks with addition of NGF every 3 days. Using intact cells, average association and dissociation rates for [3H]nicotine were 0.00021 min-1 nM-1 (n = 2) and 0.048 min-1 (n = 2), respectively, at 4 C, yielding an average apparent Kd of 229 nM. At 22 C, stable equilibrium was not attained during association studies. A similar Kd value for broken cell preparations was obtained by kinetic analysis (i.e. an average association rate of 0.00042 min-1 nM-1 and dissociation rate of 0.087 min-1), yielding an average Kd value of 207 nM (n = 2) at 4 C. By saturation binding analysis of intact cells, an average Kd of 292 nM (n = 2) and a binding capacity (Bmax) of 15,118 molecules/cell were obtained. [3H]Nicotine binding was inhibited on an equimolar basis by L- (-)nicotine and N-methylcarbamylcholine. D-(+) Nicotine was 7-fold less potent, whereas alpha-bungarotoxin, mecamylamine, and atropine showed no significant inhibition. [3H]Nicotine binding was also inhibited quantitatively by mono-specific polyclonal antibodies raised against the predicted alpha 3-subunit sequence (amino acids 130-139) of the rat neuronal nicotinic cholinergic receptor. This study represents the first biochemical characterization of NGF-stimulated nicotine-binding sites on PC 12 cells and confirms previous evidence of the presence of functional nicotinic cholinergic receptors on these cells.

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