Printed in U.S.A. ON THE SITE OF ACTION OF NICOTINE IN FROG

WEISS, GEORGE B.: On the site of action of nicotine in frog rectus abdominis muscle. J. Pharmacol. Exp. Ther. 183: 169-181, 1972. Experiments were designed to elicit information about the cellular site of action of nico-tine in frog rectus abdominis muscle. Nicotine (6.16 and 61.6 .tM) increased muscle ‘5Ca retention after a subsequent 120-minute washout, decreased total Ca content and did not alter 45Ca loss when added during the slow component phase of the washout. In-creasing p11 from 6.80 to 9.40 increased nicotine-induced ‘5Ca retention and decreased the rate of development (but not the magnitude) of the contractile response. Procaine (3.67 mM) , high K (80 mM) and d-tubocurarine (25 tM) but not acetylcholine (ACh 2.3 M) blocked contractions and increased ‘Ca retention induced by nicotine, whereas nicotine blocked contractions elicited by ACh but not those obtained with high K. Hemi-cholinium-3 partially inhibited contractions and the increased ‘5Ca retention elicited by nicotine but did not affect similar actions of ACh. These results indicate that nicotine 1) acts at receptors at the neuromuscular junction and only a portion of these may b