Involvement of Calcium, Inositol-1,4,5 Trisphosphate and Diacylglycerol in the Prothoracicotropic Hormone-Stimulated Ecdysteroid Synthesis and Secretion in the Prothoracic Glands of Bombyx mori

Ca2+ signaling in prothoracicotropic hormone-stimulated prothoracic gland cells of Manduca sexta: Evidence for mobilization and entry mechanisms

“…PTTH-stimulated IP 3 generation has not been detected in Manduca PGs (Girgenrath and Smith, 1996), but inferential evidence suggested that store-operated Ca 2+ entry (SOC), which generally is IP 3 -dependent, participates in the PTTH-stimulated increase in [Ca 2+ ] i (Birkenbeil, 1998). Likewise, in Bombyx, PTTH-stimulated IP 3 accumulation was not detected (Dedos and Fugo, 2001), yet this study also found that a phospholipase inhibitor blocked PTTH-stimulated ecdysteroidogenesis.…”

“…Studies of the effect of inhibitors of VCEC in lepidopteran PGs have provided conflicting results. Nitrendipine at concentrations of 10 mM or greater consistently inhibited ecdysteroid synthesis in both Manduca and Bombyx (Girgenrath and Smith, 1996;Dedos and Fugo, 2001) and inhibited PTTH-stimulated ERK phosphorylation in Manduca (Rybczynski and Gilbert, 2003). In contrast, a variety of dihydropyridines, verapamil and diltiazem (10-100 mM or greater) failed to inhibit the [Ca 2+ ] i response to PTTH in Manduca (Birkenbeil, 1998).…”

“…The findings that both PTTH-stimulated ERK phosphorylation and PTTH-stimulated ecdysteroid synthesis were also inhibited by U-73122 confirm the interpretation that PLC activation is an early and important step in the PTTH signal transduction pathway. This conclusion is supported by the observation that another PLC inhibitor, 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC), inhibited PTTH-stimulated ecdysteroid synthesis in Bombyx PGs, although the authors did not postulate a role for IP 3 in this system (Dedos and Fugo, 2001).…”

“…IP 3 is known to participate in the action of some peptide hormones in insects (see Gade and Auerswald, 2003) and several investigators have attempted to measure changes in IP 3 levels in PGs following stimulation with PTTH (Girgenrath and Smith, 1996;Dedos and Fugo, 2001). They were unable to detect any increase in IP 3 levels as early as 15-30 s after treatment of gland with PTTH, perhaps because IP 3 has a very short half-life in most cells.…”

“…Both nitrendipine and bepridil (a blocker of both L-and T-type VCEC) did not influence the PTTH-induced [Ca 2+ ] i response in Bombyx glands (Birkenbeil and Dedos, 2002). In two of these studies (Dedos and Fugo, 2001;Birkenbeil and Dedos, 2002), the investigators employed a saline solution rather than Grace's medium. Grace's medium contains 22 mM Mg 2+ , closely matching the 25 mM concentration in Manduca hemolymph (Jungreis, 1978), whereas the saline contained only 4 mM Mg 2+ .…”