PEPTIDE F1, AN N-TERMINALLY EXTENDED ANALOG OF FMRFAMIDE, ENHANCES CONTRACTILE ACTIVITY IN MULTIPLE-TARGET TISSUES IN LOBSTER

The physiological actions of lobster peptide Fl (TNRNFLRFamide) have b een examined on three different lobster nerve-muscle preparations (exo skeletal, cardiac and visceral). The peptide, which is found at high c oncentrations in a lobster neurosecretory gland, causes a long-lasting enhancement of contractility in each target tissue, On exoskeletal ne rve-muscle preparations, peptide F-1 has the following actions: (1) it potentiates transmitter release from nerve terminals innervating exos keletal muscle, leading to an increase in both spontaneous and nerve-e voked release of transmitter; (2) it acts directly on the muscle, in t he absence of nerve activity, to induce tonic contractions; and (3) it shows a potent desensitization that does not reverse with prolonged w ashing of the tissue, On each of the types of muscle examined, peptide F-1 is active at nanomolar concentrations and is 3-4 orders of magnit ude more potent than FMRFamide. These findings suggest that peptide F- 1 is a neurohormone with widespread myogenic actions throughout lobste r peripheral tissues, The molecular mechanism(s) by which the peptide acts are not yet known, but do not appear to involve cyclic AMP or cyc lic GMP.