Regulation of muscarinic ligand binding sites by nerve growth factor in PC12 phaeochromocytoma cells

Abstract

The rat phaeochromocytoma cell line PC12 (ref. 1) possesses many characteristics of adrenal chromaffin cells, including the ability to synthesize, store and release catecholamines in response to acetylcholine and other depolarizing agents^2–4. When exposed to 2.5S nerve growth factor (NGF), PC12 cells cease to divide, and exhibit a number of neurone-like characteristics, including the extension of neurites, development of voltage-sensitive ion channels and electrical excitability, and increased capacity to synthesize and release acetylcholine^3–8. Biochemical and pharmacological evidence indicates that both adrenal chromaffin cells and sympathetic neurones contain, in addition to ganglionic-type nicotinic receptors, muscarinic cholinergic receptors proposed to modulate catecholamine release^9–13. Catecholamine release from PC12 cells is directly stimulated by nicotinic, but not muscarinic, cholinergic agonists³. Although ion flux through acetylcholine-activated channels in PC12 cells is inhibited by high concentrations of the potent muscarinic antagonist quinuclidinyl benzilate (QNB)¹⁴, the possibility that these cells may contain functional muscarinic receptors has been largely overlooked. We show here that PC12 cells contain saturable, high-affinity binding sites for ³H-(—)-quinuclidinyl benzilate (³H-QNB), which seem pharmacologically comparable with muscarinic receptors described in rodent brain^15,16, smooth muscle^17,18 and adrenal medulla¹². Moreover, treatment with NGF produces a marked elevation of specific ³H-QNB binding. PC12 cells thus may provide a useful system for investigating the biochemical mechanisms, cellular distribution and regulation of muscarinic receptors by hormones and trophic signals.