Jm. Hinton et Rh. Osborne, EFFECTS OF PROCTOLIN AND RELATED ANALOGS ON INOSITOL PHOSPHATE PRODUCTION IN THE FOREGUT OF THE LOCUST SCHISTOCERCA-GREGARIA, Insect biochemistry and molecular biology, 26(1), 1996, pp. 111-117
Proctolin (10 nM and 0.5 mu M) stimulated dose-dependent release of [H
-3]inositol 1,4,5-trisphosphate ([H-3]IP3) and [H-3]inositol 1,3,4,5-t
etrakisphosphate ([H-3]IP4) from locust foregut homogenates incubated
in Tris buffer containing [H-3]myo-inositol. Of the other analogues te
sted for agonist activity in this preparation, the order of potency wa
s proctolin >[p-F-L-phenylalanine(2)]proctolin > [alpha-methyl-L-tyros
ine(2)]proctolin > RYT > cycloproctolin. [N-methyl-L-tyrosine(2)]proct
olin was unable to induce significant release of [H-3]inositol phospha
tes. Incubation of foregut homogenates in Tris buffer containing [alph
a-methyl-L-tyrosine(2)] proctolin (10 nM) significantly reduced procto
lin-stimulated release of [H-3]IP3 and [H-3]IP4 by 86 and 63% respecti
vely, Increasing the dose of antagonist to 1 mu M did not result in fu
rther reduction of proctolin-stimulated [H-3]IP3 release although the
level of [H-3]IP4 production was reduced by 89%. Cycloproctolin and th
e tripeptide RYT were less potent antagonists of proctolin-stimulated
[H-3]inositol phosphate release than [alpha-methyl-L-tyrosine(2)] proc
tolin only causing inhibition in excess of 80% at a concentration of 1
mu M These data provide good evidence that the locust foregut contain
s a proctolin receptor, which when stimulated, causes phosphatidylinos
itol hydrolysis resulting in the production of the putative second mes
sengers molecules IF3 and IF4.