Antagonism of nicotinic receptors of rat chromaffin cells by N,N,N-trimethyl-1-(4-trans-stilbenoxy)-2-propylammonium iodide: a patch clamp and ligandbinding study

1 The effect of the oxystilbene derivative F3 was tested on nAChRs of whole -cell patch-clamped rat chromaffin cells in vitro and of rat adrenal gland membranes using I-125-epibatidine. 2 F3 (30 nM) rapidly and reversibly blocked inward currents generated by pu lse applications of nicotine, shifting the dose-response curve to the right in a parallel fashion without changing the maximum response. The action of F3 was voltage insensitive and not due to altered current reversal potenti al. 3 The R isomer of F3 war more potent (IC50=350+/-30nM) than its S-enantiome r (IC50 = 1.5 +/- 0.3 mu M). Nicotine-evoked currents were insensitive to 1 0 mu M alpha-bungarotoxin. 4 Equi-amplitude currents evoked by nicotine or epibatidine were similarly antagonized by R-F3 in a reversible fashion. Epibatidine-evoked currents re adily produced receptor desensitization. 5 Adrenal membranes specifically bound I-125-epibatidine with a single popu lation of binding sites endowed with high affinity (K-D = 159 pM) and B-max of 6.5 +/- 1.3 fmol mg(-1) of protein. 6 I-125-epibatidine binding was specifically displaced by cytisine (K-i = 6 8 nM) or ACh (K-i = 348 nM). F3 specifically displaced I-125-epibatidine bi nding although with lower affinity (K-i = 29.6 mu M) than in electrophysiol ogical experiments. I-125-epibatidine binding to rat adrenal tissue was ins ensitive to alpha-bungarotoxin which readily antagonized I-125-epibatidine binding to bovine adrenal tissue. 7 The present results suggest that F3 is a relatively potent and apparently competitive antagonist of nAChRs on rat chromaffin cells. Since previous s tudies have indicated that F3 targets different subtypes on chick neuronal tissue, it appears that nAChRs display interspecies differences to be consi dered for drug development studies.