CHARACTERIZATION OF ACTIONS OF LEUCOPHAEA TACHYKININ-RELATED PEPTIDES(LEMTRPS) AND PROCTOLIN ON COCKROACH HINDGUT CONTRACTIONS

The nine Leucophaea Tachykinin-Related Peptides (LemTRP 1-9) isolated from the midgut and brain of the cockroach, Leucophaea maderae, all in duced increases in spontaneous contractions of the L. maderae hindgut. Synthetic LemTRP 1 and 3-9, were equally potent in inducing contracti ons of the hindgut. More than seven of the nine C-terminal residues of the closely related locust peptide locustatachykinin I (LomTK I) are required for full activity of the peptide on the L. maderae hindgut. P roctolin, a well characterized myostimulatory neuropeptide, was shown to be more potent than LemTRPs. LemTRP 1 and proctolin did not have sy nergistic actions in potentiating the amplitude and tonus of contracti ons of the L. maderae hindgut. Several differences could be seen in ac tions of LemTRP 1 and proctolin. In contrast to proctolin, LemTRP 1 co uld not override the inhibitory action of 10(-9) M of the myoinhibitor y peptide leucomyosuppressin. Spantide I, an antagonist of the mammali an tachykinin receptors, at a concentration of 5 mu M, blocked the res ponse to LemTRP 1, but not to proctolin. The competitive proctolin rec eptor antagonist [alpha-methyl-L-tyrosine(2)]-proctolin blocked the ac tion of both proctolin and LemTRP 1 when applied at 1 mu M, whereas cy cloproctolin had no antagonist action on either peptide. Verapamil, a blocker of voltage gated Ca2+-channels, and the less specific Ca2+-cha nnel blocker Mn2+, abolished the action of LemTRP 1, but not of procto lin. The results obtained indicate that LemTRPs act on receptors disti nct from those of proctolin. Double label immunocytochemistry revealed that all LomTK-like immunoreactive fibers impinge on the proctolinerg ic fibers in the hindgut. This finding and the inhibitory actions of C a2+-channel blockers on TRP responses and of the proctolin receptor an tagonist on both peptides, may suggest that the LemTRP receptors are n ot on the hindgut muscle fibers but on the terminals of the proctoline rgic neurons. Thus, LemTRPs may induce release of proctolin on the hin dgut. An alternative is that LemTRPs act by mechanisms clearly distinc t from those of proctolin. (C) 1998 Elsevier Science Inc.