Pharmacological study of signal transduction during stimulation of prothoracic glands from Manduca sexta

Cytosolic free calcium, [Ca2+]i, measured in individual prothoracic gland cells of Manduca sexta with Fura-2 was increased by prothoracicotropic hormone, PTTH, and by mastoparan, a wasp venom peptide, activating G proteins. The effect on [Ca2+]i of mastoparan and of PTTH was inhibited by cadmium and the antagonist of T-type calcium channels, amiloride, and not influenced by the L-type calcium channel blocker nitrendipine, suggesting that the same or similar plasma membrane channels are involved in the action of mastoparan and of PTTH. Pertussis toxin prevented the mastoparan-induced increase of [Ca2+]i, whereas the effect of PTTH is not influenced by pertussis toxin. Intracellular addition of GDP-β-S failed to inhibit the PTTH-stimulated increase in [Ca2+]i suggesting that G proteins are not involved in the stimulatory mechanism of PTTH.