Investigation of presumptive mobilization pathways for calcium in the steroidogenic action of big prothoracicotropic hormone.
Ecdysteroidogenesis in the prothoracic glands of the tobacco hornworm Manduca sexta is stimulated by the cerebral neuropeptide prothoracicotropic hormone (PTTH). PTTH-stimulated cAMP synthesis and ecdysone secretion are dependent on the presence of extracellular calcium, suggesting that PTTH enhances calcium entry into the cytosol. Such entry into the cytosol might involve the opening of a plasma membrane calcium channel, or a mechanism dependent upon prior inositol triphosphate (IP3)-mediated release of intracellularly stored calcium. In pupal prothoracic glands, PTTH does not increase IP3 or other inositol phosphates over-times ranging from seconds up to 30 min, even in the presence of lithium. However, the L-type calcium channel antagonist nitrendipine completely prevents PTTH-stimulated ecdysone synthesis. A 41 kDa G-protein in prothoracic glands is ADP-ribosylated by pertussis toxin. However, PTTH-stimulated ecdysone synthesis is unaffected by prior exposure to pertussis toxin, indicating that the 41 kDa protein is not involved in the acute stimulation of steroidogenesis. By contrast, cholera toxin has a stimulatory effect on ecdysone secretion suggesting the involvement of a Gs-like protein. Based on the absence of PTTH-stimulated inositol phosphate formation in pupal prothoracic glands, it is suggested that calcium mobilization may occur through the opening of a calcium channel, possibly regulated by Gs.
Girgenrath
S
S
Department of Biology, Northeastern University, Boston, MA 02115, USA.
Smith
W A
WA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002772:Cholera Toxin / Q000494:pharmacology; D004440:Ecdysone / Q000096:biosynthesis; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D007301:Insect Hormones / Q000502:physiology*; D018402:Manduca / Q000378:metabolism*; D009568:Nitrendipine / Q000494:pharmacology; D037342:Pertussis Toxin; D015290:Second Messenger Systems; D010738:Type C Phospholipases / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002121:Calcium Channel Blockers; D007295:Inositol Phosphates; D007301:Insect Hormones; D010566:Virulence Factors, Bordetella; D004440:Ecdysone; C009089:prothoracicotropic hormone; D015544:Inositol 1,4,5-Trisphosphate; D002772:Cholera Toxin; D009568:Nitrendipine; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium