Different Ca 2+ signalling cascades manifested by mastoparan in the prothoracic glands of the tobacco hornworm, Manduca sexta , and the silkworm, Bombyx mori

Application of the tetradecapeptide mastoparan to the prothoracic glands (PGs) of the tobacco hornworm, Manduca sexta , and the silkworm, Bombyx mori , resulted in increases in intracellular Ca 2+ ([Ca 2+ ] i ). In M. sexta , Gi proteins are involved in the mastoparan‐stimulated increase in [Ca 2+ ] i . However, there is no involvement of Gi proteins in the mastoparan‐stimulated increase in [Ca 2+ ] i in prothoracic gland cells from B. mori . Unlike in M. sexta prothoracic glands, in B. mori prothoracic glands mastoparan increases [Ca 2+ ] i even in the absence of extracellular Ca 2+ . Pharmacological manipulation of the Ca 2+ signalling cascades in the prothoracic glands of both insect species suggests that in M. sexta prothoracic glands, mastoparan's first site of action is influx of Ca 2+ through plasma membrane Ca 2+ channels while in B. mori prothoracic glands, mastoparan's first site of action is mobilization of Ca 2+ from intracellular stores. In M. sexta , the combined results indicate the presence of mastoparan‐sensitive plasma membrane Ca 2+ channels, distinct from those activated by prothoracicotropic hormone or the IP 3 signalling cascade, that coordinate spatial increases in [Ca 2+ ] i in prothoracic gland cells. We propose that in B. mori , mastoparan stimulates Ca 2+ mobilization from ryanodine‐sensitive intracellular Ca 2+ stores in prothoracic gland cells. Arch. Insect Biochem. Physiol. 65:52–64, 2007. © 2007 Wiley‐Liss, Inc.