More than 450 ventricles, isolated from 51 species of bivalve molluscs, were surveyed for their responses to the molluscan cardioactive neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH(,2)). The responses were diverse, ranging from excitation to inhibition, but over half of the species were only excited by the peptide, and only two were exclusively inhibited. Oysters were notably insensitive. FMRFamide also caused catch contractures of the anterior byssus retractor muscle (ABRM) of Geukensia demissa which were indistinguishable from those of acetylcholine (ACh). Nevertheless, their mechanisms of action differed. FMRFamide contractures were less Na-dependent, although extracellular Na was necessary for catch. FMRFamide caused a larger influx of Ca than did ACh, but, in Ca-free ASW, FMRFamide also had access to intracellular Ca that could not be released by ACh. Neither agent affected cyclic nucleotide levels in the muscle. The specificity of the FMRFamide response in the ABRM and two hearts (Macrocallista nimbosa which is excited by the peptide, and Lampsilis claibornensis which is inhibited) were examined in detail. The C-terminal amide and Arg('3) residue are critical to FMRFamide-like activity on all three preparations; extensions or substitutions at the N-terminal are less deleterious. The three preparations differ in specificity, however. Lampsilis hearts are the least restrictive, especially with respect to the Arg('3) residue. The ABRMs are consistently more sensitive to analogs with extensions at the N-terminal, but the increase in sensitivity is relatively small compared to other preparations. The effects of FMRFamide on cAMP levels in hearts of Lampsilis claibornensis were also examined. FMRFamide inhibition is accompanied by a dose-dependent and time-dependent increase in cAMP. But the increase follows the change in mechanical activity, indicating that / cAMP does not cause the early inhibitory effects of the peptide. It is not clear whether the cAMP is elevated as a direct result of FMRFamide-receptor interaction, or whether it is elevated indirectly, as a result of the inhibition. In either case, it might serve a homeostatic function. / Source: Dissertation Abstracts International, Volume: 42-07, Section: B, page: 2661. / Thesis (Ph.D.)--The Florida State University, 1981.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74585 |
| Contributors | PAINTER, SHERRY D'AUN., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 167 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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