THE EFFECTS OF CALLIFMRFAMIDES AND OTHER FMRFAMIDE-RELATED NEUROPEPTIDES ON THE ACTIVITY OF THE HEART OF THE BLOWFLY CALLIPHORA-VOMITORIA

A series of six neuropeptides, designated calliFMRFamides, isolated from the thoracic ganglion of the blowfly Calliphora vomitoria were tested for their effects on a semi-isolated blowfly heart preparation. Despite the close structural similarities of the nonapeptides, only two were active. CalliFMRFamide 5 (APGQDFMRFamide) at concentrations of 10(-6)-10(-8)M was effective in increasing both the frequency and amplitude of the heart beat whereas calliFMRFamide 1 (TPQQDFMRFamide) at the same concentrations caused only an increase in frequency of the beat. The non-amidated analogues of these two peptides were inactive, as were calliFMRFamides 2, 3 and 4 (TPSQDFMRFamide, SPSQDFMRFamide and KPNQDFMRFamide) and their non-amidated analogues. CalliFMRFamide 6 (ASGQDFMRFamide), differing from the active calliFMRFamide 5 only by the serine for proline substitution at the second position from the N-terminus, was also inactive. The molluscan cardioacceleratory neuropeptide FMRFamide, at concentrations up to 10(-5)M was inactive on the C. vomitoria heart preparation. SchistoFLRFamide, cardioinhibitory in the locust, was inactive on the blowfly heart preparation at concentrations of 10(-10)-10(-5)M whereas leucomyosuppressin, a cockroach gut inhibitory neuropeptide, inhibited the heart of C. vomitoria at a concentration of 10(-6)M. These results indicate a high specificity for neuropeptide-receptor interactions on the heart of the blowfly, with a pronounced emphasis on changes in conformation imposed by variations in the N-terminus.