Meeting Abstract

P3.71  Saturday, Jan. 5  Pharmacological Characterization of the Earthworm Gizzard Cholinergic Receptor KRAJNIAK, K.G.*; ONYANGO, E.; Southern Ill. Univ. Edwardsville; Southern Ill. Univ. Edwardsville kkrajni@siue.edu

Previous work in our laboratory has shown that the contractions of the isolated earthworm crop-gizzard can be modified by several different neurotransmitters including acetylcholine. In Lumbricus terrestris acetylcholine has a biphasic effect on the amplitude of contraction, with an excitatory effect at lower doses (threshold of approximately 10^-7M) and an inhibitory effect at higher doses (threshold of approximately 10^-5M). In an attempt to pharmacologically characterize this receptor isolated gizzard rings were exposed to several different muscarinic and nicotinic agonists ranging in concentration from 10^-12M to 10^-4M. These included the muscarinic agonists muscarine and McN-A-343; the nicotinic agonists nicotine and epibatidine, and the nonselective agonist carbachol. The nicotinic drugs had a much more subdued effect on the gizzard as compared to the muscarinic ones, which duplicated the previously mentioned biphasic effect on amplitude; with a threshold of approximately 10^-7M for excitation and 10^-5M to 10^-4M for inhibition for both muscarine and McN-A-343. Interestingly enough, the non-selective agonist carbachol had the greatest effect on amplitude of contraction, showing excitation with a threshold level of approximately 10^-7M. Based on these results and previous research we suggest that the receptors found in the L. terrestris gut appear to belong pharmacologically to the muscarinic class of cholinergic receptors.