Ca+ signaling in prothoracicotropic hormone-stimulated prothoracic gland cells of Manduca sexta: Evidence for mobilization and entry mechanisms

Prothoracicotropic hormone (PTTH) stimulates ecdysteroidogenesis in lepidopteran prothoracic glands (PGs), thus indirectly controlling molting and metamorphosis. PTTH triggers a signal transduction cascade in PGs that involves an early influx of Ca(2+). Although the importance of Ca(2+) has been lon...

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Bibliographic Details
Published in:Insect biochemistry and molecular biology 2005, Vol.35 (4), p.263-275
Main Authors: Fellner, S.K, Rybczynski, R, Gilbert, L.I
Format: Article
Language:English
Subjects:
calcium
calcium channels
calcium entry
calcium mobilization
enzyme inhibitors
extracellular-signal regulated kinase
hormonal regulation
inositol phosphates
ion transport
Manduca sexta
phospholipase C
phosphorylation
protein kinases
prothoracic glands
prothoracicotropic hormone
signal transduction
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Summary:Prothoracicotropic hormone (PTTH) stimulates ecdysteroidogenesis in lepidopteran prothoracic glands (PGs), thus indirectly controlling molting and metamorphosis. PTTH triggers a signal transduction cascade in PGs that involves an early influx of Ca(2+). Although the importance of Ca(2+) has been long known, the mechanism(s) of PTTH-stimulated changes in cytoplasmic Ca(2+) [Ca(2+)]i are not yet well understood. PGs from the fifth instar of Manduca sexta were exposed to PTTH in vitro. The resultant changes in [Ca(2+)]i were measured using ratiometric analysis of a fura-2 fluorescence signal in the presence and absence of inhibitors of specific cellular signaling mechanisms. The phospholipase C (PLC) inhibitor U-73122 nearly abolished the PTTH-stimulated increase in [Ca(2+)]i, as well as PTTH-stimulated ecdysteroidogenesis and extracellular-signal regulated kinase phosphorylation, thus establishing a role for PLC and implicating inositol trisphosphate (IP3) in PTTH signal transduction. Two antagonists of the IP3 receptor, 2-APB and TMB-8, likewise blocked the [Ca(2+)]i response by a mean of 92%. We describe for the first time the presence of Ca(2+) oscillations in PTTH-stimulated cells in Ca(2+)-free medium. External Ca(2+) entered PG cells via at least two routes: store-operated (capacitative) Ca(2+) entry channels and L-type voltage-gated Ca(2+) channels. We propose that PTTH initiates a transductory cascade typical of many G-protein coupled receptors, involving both Ca(2+) mobilization and entry pathways.
ISSN:0965-1748
1879-0240
DOI:10.1016/j.ibmb.2004.11.006