| Abstract: | The cytosolic free calcium was measured with Fura-2 in single prothoracic gland cells of Galleria larvae. During the last two larval instars calcium concentration correlated with ecdysone secretion by the glands. Addition of prothoracicotropic hormone (PTTH) from brains of Galleria larvae to prothoracic glands in vitro induced a significant increase in calcium in the gland cells. This effect of PTTH was abolished by removal of extracellular calcium, or by the addition of lanthanum or of the calcium channel antagonists nicardipine and verapamil. The calcium channel agonist Bay K 8644 evoked an increase in intracellular calcium. TMB-8, an inhibitor of intracellular calcium mobilization, did not block the PTTH-stimulated rise in calcium concentration or ecdysone production, indicating that intracellular calcium stores are not involved in the calcium-mediated ecdysone synthesis. Moreover, PTTH seems to exert its action by influencing dihydropyridine-sensitive calcium channels in the plasma membrane. © 1996 Wiley-Liss, Inc. |
