Effects of cholecystokinin, gastrin, and related peptides on coho salmon gallbladder contraction in vitro.
UNLABELLED: Isometric contractions of coho salmon (Oncorhynchus kisutch) gallbladder longitudinal muscle strips were recorded in response to porcine cholecystokinin (CCK), octapeptide of CCK (OP-CCK), desulfated octapeptide of CCK (ds-OP-CCK), porcine heptadecapeptide gastrins I and II, and pentagastrin. Peak tonic contraction amplitude and peak rhythmic contraction frequency were used to construct concentration-response curves for each peptide. Observed maximal responses to each peptide were not significantly different; therefore, all peptides tested were equal in efficacy. CCK, OP-CCK, and gastrin II were equipotent, and ds-OP-CCK and gastrin I were equipotent. CONCLUSIONS: 1) porcine CCK can stimulate contraction of the coho salmon gallbladder; 2) tonic and rhythmic contractile responses are elicited in coho salmon gallbladder by agonists; 3) coho salmon gallbladder muscle cannot distinguish between agonists that differ in the location of a sulfated tyrosyl residue at position 6 versus position 7 from the C-terminus; and 4) the results of this study are consistent with the hypothesis that coho salmon gallbladder muscle contains a relatively primitive CCK receptor.
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