Regulation of capacitative Ca2+ entry by prothoracicotropic hormone in the prothoracic glands of the silkworm, Bombyx mori.
Measurements of Ca2+ influx in Fura-2/AM loaded steroidogenic cells (prothoracic glands; PGs) of the silkworm, Bombyx mori showed that application of the neuropeptide prothoracicotropic hormone (PTTH) can increase the intracellular [Ca2+]i. This PTTH-mediated Ca2+ influx in PG cells had kinetic patterns and pharmacological characteristics similar to those induced by thapsigargin. Namely, it produced increases in intracellular Ca2+ levels only in the presence of extracellular Ca2+, it was blocked by Gd3+ and 2-Aminoethoxydiphenylborate (2-APB), and it was unaffected by several toxins or compounds that block voltage-activated Ca2+ channels. Moreover, the PTTH-stimulated increase of Ca2+ levels was eliminated in the presence of heparin (an IP3 receptor blocker), and by TMB-8 which also blocked any PTTH-dependent increase of ecdysteroid secretion. The PTTH-mediated increase of Ca2+ levels was not affected by the non-hydrolysable GDP analogue, GDPbetaS, an indication that a G protein is not downstream of the PTTH receptor. These results argue strongly in favor of gating by the PTTH receptor of capacitative Ca2+ entry (CCE) channels (or store-operated Ca2+ channels (SOCs)) by a mechanism that does not involve any G proteins but requires the presence of functional IP3 receptors. Because the ability of PTTH to stimulate the [Ca2+]i levels of PG cells was completely mimicked by thapsigargin and exhibited a pharmacological profile similar to CCE mechanisms, we believe that PTTH directly regulates a CCE pathway in PG cells thereby activating a plethora of downstream regulators responsible for ecdysteroid secretion by the PGs of Bombyx mori.
Dedos
Skarlatos G
SG
Saxon Academy of Sciences at Leipzig, Dept. Neurohormones, PF 100322, 07703 Jena, Germany. sd323@cam.ac.uk
Wicher
Dieter
D
Fugo
Hajime
H
Birkenbeil
Heiner
H
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D012831:Bombyx / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology; D005682:Gadolinium / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D007301:Insect Hormones / Q000502:physiology*; D007814:Larva / Q000187:drug effects / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
D007301:Insect Hormones; C009089:prothoracicotropic hormone; D019284:Thapsigargin; D006493:Heparin; D005682:Gadolinium; D019204:GTP-Binding Proteins; D002118:Calcium