Diuretic and myotropic activities of N-terminal truncated analogs of Musca domestica kinin neuropeptide

Musca kinin (Musdo-K; NTVVLGKKQRFHSWG-NH2) and N-terminal truncated analogs of 4–14 residues in length were assayed for diuretic and myotropic activity on housefly Malpighian tubules and hindgut, respectively. The pentapeptide was the minimum sequence required for biological activity, but it was > 5 orders of magnitude less potent than the intact peptide. The pharmacological profiles of the different analogs in the two assays were very similar, suggesting the same receptor is present on both tissues. Potency was little affected by the deletion of Asn1, but was reduced > 10-fold after the removal of Thr2. Deletion of the next 5 residues had relatively little effect, but after the second lysyl residue (Lys8) was removed potency fell by one to two orders of magnitude. There was a similar drop in potency after the removal of Arg10, and at 100 μM the pentapeptide had only 20% of the diuretic activity of the intact peptide. The importance of Arg10 was confirmed by comparing dose-response curves for Musdo-K [6–15] and Acheta kinin-V (AFSHWG-NH2) in the diuretic assay; the substitution of arginine by alanine produced a significant reduction in potency and some loss of activity