title: Mode of action of an inhibitory neuropeptide SchistoFLRFamide on the locust oviduct visceral muscle.
abstract: The possible mode of action of an inhibitory neuropeptide SchistoFLRFamide (PDVDHVFLRFamide) on locust oviduct visceral muscle was studied by examining its ability to inhibit calcium ionophore A23187-, caffeine- or phorbol ester-induced oviduct contractions. A23187-induced muscle contractions included two components: one which required the influx of extracellular Ca2+ through Ca2+ channels (blocked by cobalt ions), the other not blocked by cobalt ions. SchistoFLRFamide inhibited the cobalt-sensitive components, but not the latter. Caffeine induced two phases of contractions, a phasic contraction which was probably due to the release of intracellular Ca2+ and a tonic contraction which required the influx of extracellular Ca2+. SchistoFLRFamide inhibited the tonic contraction in a dose-dependent manner but did not influence the phasic contraction. The phorbol 12-myristate 13-acetate-induced muscle contraction required the presence of extracellular Ca2+, with Ca2+ probably entering through ligand-gated channels, but the contraction was not inhibited by SchistoFLRFamide. Based upon these results, it appears that SchistoFLRFamide inhibits muscle contraction by preventing the accumulation of free intracellular Ca2+ from extracellular stores. SchistoFLRFamide is incapable of inhibiting contraction induced by the release of intracellular stores of Ca2+. It is possible that SchistoFLRFamide closes or blocks voltage-gated and some ligand-gated Ca2+ channels in the plasma membrane.
authors.affiliation: Department of Zoology, University of Toronto, Ontario, Canada.
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: I
authors.initials: I
authors.lastname: Orchard
authors.forename: A B
authors.initials: AB
authors.lastname: Lange
authors.forename: X
authors.initials: X
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects; D003035:Cobalt / Q000494:pharmacology; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D006110:Grasshoppers; D015640:Ion Channel Gating / Q000187:drug effects; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009479:Neuropeptides / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D010057:Oviducts / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D009479:Neuropeptides; C059573:SchistoFLRFamide; D000001:Calcimycin; D003035:Cobalt; D002110:Caffeine; C018021:cobaltous chloride; D009543:Nifedipine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium