Proctolin antagonists bind to [(3)H]proctolin binding sites in the locust hindgut.
Proctolin caused dose-dependent (1-200 nM) contraction of the isolated hindgut of S. gregaria which was abolished by [alpha-methyl-L-tyrosine(2)]-proctolin (1 microM). In comparison, cycloproctolin (5 microM) reduced the proctolin maximum response by 41%. Hindgut homogenates contained [(3)H]proctolin binding sites with a K(d) value of 660 nM, a B(max) value of 23.8 pmol/mg protein and a Hill coefficient of 0.934. Cycloproctolin (IC(50,) 220 nM; K(i), 204 nM), unlabeled proctolin (IC(50) 680 nM) and [alpha-methyl-L-tryosine(2)]-proctolin (IC(50) 3.1 microM, K(i), 2.9 microM) but not SchistoFLRFamide (1 nM-10 microM) were capable of displacing bound [(3)H]proctolin.
Gray
A S
AS
Insect Neuroscience Group, Department of Biological and Biomedical Sciences, University of the West of England, Frenchay Campus, Coldharbour Lane, Bristol, UK.
Hancock
J T
JT
Osborne
R H
RH
D000818:Animals; D001665:Binding Sites; D006110:Grasshoppers / Q000187:drug effects*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D009479:Neuropeptides; D018377:Neurotransmitter Agents / Q000494:pharmacology; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology*; D009842:Oligopeptides / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D014316:Tritium; D014781:Viscera / Q000187:drug effects / Q000378:metabolism
D009479:Neuropeptides; D018377:Neurotransmitter Agents; D014179:Neurotransmitter Uptake Inhibitors; D009842:Oligopeptides; D014316:Tritium; C011536:proctolin