Journal of comparative physiology

, Volume 148, Issue 4, pp 491–501 | Cite as

FMRFamide catch contractures of a molluscan smooth muscle: Pharmacology, ionic dependence and cyclic nucleotides

  • S. D. Painter


  1. 1.

    Both acetylcholine (A Ch) and the molluscan neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) set catch in the anterior byssus retractor muscle (ABRM); catch is relaxed by 5-hydroxytryptamine (5 HT).

  2. 2.

    The threshold for FMRFamide contracture is 3- to 30-fold lower than for ACh; and low to moderate doses of FMRFamide are more potent than equivalent doses of ACh. At very high concentrations, however, FMRFamide contractures are less forceful than those to ACh.

  3. 3.

    FMRFamide contractures are diminished less than ACh contractures in Na-free medium, but contractures are phasic in either case.

  4. 4.

    FMRFamide contractures decline much more slowly than ACh contractures in Ca-free ASW and La-ASW. Thus, FMRFamide may have access to a more slowly exchanging pool of intracellular Ca; alternatively, the mechanisms coupling excitation and contraction may differ for the two agonists, with the FMRFamide coupling mechanism being less sensitive to Ca depletion.

  5. 5.

    Neither FMRFamide nor ACh effect cAMP levels in the ABRM; and no effect on cGMP levels was detected.

  6. 6.

    Cyclic AMP is increased by 5 HT and Na-free ASW, but not by 8-bromoguanosine 3′∶5′-cyclic monophosphate. Thus, relaxation is not always accompanied by increased cAMP levels.

  7. 7.

    Immunoreactive FMRFamide is present in the ABRM; thus, its actions are of physiological as well as pharmacological interest.



cAMP Level cGMP Level FMRFamide Cyclic Monophosphate Increase cAMP Level 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



anterior byssus retractor muscle










adenosine 3′∶5′-cychic monophosphate


guanosine 3′∶5′-cyclic monophosphate


8-bromoadenosine 3′∶5′-cyclic monophosphate


8-bromoguanosine 3′∶5′-cyclic monophosphate




d-tubocurarine chloride


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Copyright information

© Springer-Verlag 1982

Authors and Affiliations

  • S. D. Painter
    • 1
  1. 1.Department of Biological ScienceFlorida State UniversityTallahasseeUSA

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