Leu(10) of alpha-conotoxin PnIB confers potency for neuronal nicotinic responses in bovine chromaffin cells

Two alpha-conotoxins PnIA and PnIB (previously reported as being "mollusc s pecific") which differ in only two amino acid residues (AN versus LS at res idues 10 and 11, respectively), show markedly different inhibition of the n euronal nicotinic acetylcholine receptor response in bovine chromaffin cell s, a mammalian preparation. Whereas alpha-conotoxin PnIB completely inhibit s the nicotine-evoked catecholamine release at 10 mu M, with IC50 = 0.7 mu M, alpha-conotoxin PnIA is some 30-40 times less potent. Two peptide analog ues, [A10L]PnIA and [N11S]PnIA were synthesized to investigate the extent t o which each residue contributes to activity. [A10L]PnIA (IC50 = 2.0 mu M) completely inhibits catecholamine release at 10 mu M whereas [N11S]PnIA sho ws Little inhibition. In contrast, none of the peptides inhibit muscle-type nicotinic responses in the rat hemi-diaphragm preparation. We conclude tha t the enhanced potency of alpha-conotoxin PnIB over alpha-conotoxin PnIA in the neuronal-type nicotinic response is principally determined by the larg er, more hydrophobic leucine residue at position 10 in alpha-conotoxin PnIB . (C) 2000 Elsevier Science B.V. All rights reserved.