UP-REGULATION OF HUMAN ALPHA-7 NICOTINIC RECEPTORS BY CHRONIC TREATMENT WITH ACTIVATOR AND ANTAGONIST LIGANDS

This study examined the binding and functional properties of human alp ha 7 neuronal nicotinic acetylcholine receptors stably expressed in hu man embryonic kidney (HEK) 293 cells following chronic treatment with nicotinic receptor ligands. Treatment of cells with (-)-nicotine(100 m u M) for 120 h increased the B-max values of [I-125] alpha-bungarotoxi n binding 2.5-fold over untreated cells. This effect was concentration -dependent (EC50 = 970 mu M) and a 6-fold upregulation was observed wi th the maximal concentration of (-)-nicotine tested. Also, treatment o f cells with ligands of varying intrinsic activities including (+/-)-e pibatidine, (2,4)-dimethoxybenzylidene anabaseine (GTS-21) and 1,1-dim ethyl-4-phenyl piperazinium iodide (DMPP) also upregulated [I-125] alp ha-bungarotoxin binding, A concentration-dependent upregulation of bin ding sites was also observed following treatment with the alpha 7 nico tinic receptor antagonist, methyllycaconitine (EC50 = 92 mu M) With a maximal upregulation of about 7-fold. Functionally, the peak amplitude of the whole-cell currents recorded by fast application of(-)-nicotin e after chronic treatment of cells with concentrations of(-)-nicotine (1000 mu M) or methyllycaconitine (10 mu M) that elicited similar incr eases in binding levels (3.5-fold) resulted in increases of 2-fold (50 5 +/- 21 pA) and 6-fold (1820 +/- 137 pA) respectively in whole cell c urrent amplitude compared to untreated cells (267 +/- 24 pA), These st udies clearly demonstrate that long-term exposure to both activator an d antagonist ligands can increase the density of alpha 7 nicotinic rec eptors and can differentially enhance nicotinic receptor function. (C) 1998 Elsevier Science B,V.