Biological actions of synthetic locust ion transport peptide (ITP)

Locust Ion Transport Peptide (ITP) a member of the arthropod neuropeptide f amily which includes hyperglycemic, vitellogenesis-inhibiting, and moult-in hibiting hormones (CHH, VIH, MIH, respectively) was synthesized as proposed by Meredith et al. (1996) with terminal amidation of amino acid residue 72 and with 3 disulphide bridges. This is the first member of this family to be synthesized. Biological activities of synthetic ITP (synITP) were very s imilar to those previously reported for ITP purified from Schistocerca corp ora cardiacs (ScgITP) and partially sequenced by Audsley et al. (1992a, b). Dose-response curves for both synITP and ScgITP on ileal transport of Cl- (measured as increased short-circuit current, Delta I-sc), were similar wit h a EC50 of 1-2 nM. The I-sc time course and maximum Delta I-sc across ilea l epithelia at different dosages of synITP and ScgITP had similar patterns as did changes in transepithelial open-circuit potential (V-t) and resistan ce (R-t), reflecting changes in salt transport which drives fluid absorptio n. Disulphide bridges were shown to be required for biological activity of synITP, which caused the same 4-fold increase in ileal fluid transport rate (J(v)) as previously reported for ScgITP. Both synITP and ScgITP caused on ly partial stimulation of rectal I-sc and had no significant effect on rect al J(v). These results indicate that the structure of ITP predicted earlier from cDNA is correct. (C) 1999 Elsevier Science Ltd. All rights reserved.