Effects Of Chronic Nicotinic Ligand Exposure On Functional Activity Of Nicotinic Acetylcholine Receptors Expressed By Cells Of The Pc12 Rat Pheochromocytoma Or The Te671/Rd Human Clonal Line
Abstract: Studies were conducted to ascertain the temporal and doseâ€dependent effects of nicotinic ligand exposure on functional activity of different nicotinic acetylcholine receptor (nAChR) subtypes, as expressed by cells of the PC12 rat pheochromocytoma (gangliaâ€type nAChR) or the TE671/RD human (muscleâ€type nAChR) clonal line. Chronic (3â€“72â€h) agonist (nicotine or carbamylcholine) treatment of cells led to a complete (TE671) or nearly complete (PC12) loss of functional nAChR responses, which is referred to as â€œfunctional inactivation.â€Some inactivation of nAChR function was also observed for the nicotinic ligands dâ€tubocurarine (dâ€TC), mecamylamine, and decamethonium. Halfâ€maximal inactivation of nAChR function was observed within 3 min for TE671 cells and within 10 min for PC12 cells treated with inactivating ligands. Functional inactivation occurred with dose dependencies that could not always be reconciled with those obtained for acute agonist activation of nAChR function or for acute inhibition of those responses by dâ€TC, decamethonium, or mecamylamine. Treatment of TE671 or PC12 cells with the nicotinic antagonist pancuronium or alcuronium alone had no effect on levels of expression of functional nAChRs. However, evidence was obtained that either of these antagonists protected TE671 cell muscleâ€type nAChRs or PC12 cell gangliaâ€type nAChRs from functional inactivation on longâ€term treatment with agonists. Recovery of TE671 cell nAChR function following treatment with carbamylcholine, nicotine, or dâ€TC occurred with halfâ€times of 1â€“3 days whether cells were maintained in situ or harvested and replated after removal of ligand. By contrast, 50% recovery of functional nAChRs on PC12 cells occurred within 2â€“6 h after drug removal. In either case the time course for recovery from nAChR functional inactivation is much slower than recovery from nAChR â€œfunctional desensitization,â€which is a reversible process that occurs on shorterâ€term (0â€“5â€min) agonist exposure of cells. These results indicate that gangliaâ€type and muscleâ€type nAChRs are similar in their sensitivities to functional inactivation by nicotinic ligands but differ in their rates of recovery from and onset of those effects. The ability of drugs such as the agonists dâ€TC, decamethonium, and mecamylamine to induce functional inactivation may relate to their activities as partial/full agonists, channel blockers, and/or allosteric regulators. Effects of drugs such as pancuronium and alcuronium are likely to reflect simple competitive inhibition of primary ligand binding at functional activation sites. Agonistâ€induced functional inactivation of TE671 cell nAChRs occurs under conditions previously shown to induce increases in numbers of nAChR ligand binding sites expressed on the cell surface and in total membrane pools and contrasts with coordinate downâ€regulation of nAChR ligand binding and function following chronic agonist treatment of nAChRâ€bearing cells in the periphery. Copyright Â© 1991, Wiley Blackwell. All rights reserved
Journal of Neurochemistry
Digital Object Identifier (DOI)
Lukas, Ronald J., "Effects Of Chronic Nicotinic Ligand Exposure On Functional Activity Of Nicotinic Acetylcholine Receptors Expressed By Cells Of The Pc12 Rat Pheochromocytoma Or The Te671/Rd Human Clonal Line" (1991). Neurobiology. 212.