Different Ca2+ signalling cascades manifested by mastoparan in the prothoracic glands of the tobacco hornworm, Manduca sexta, and the silkworm, Bombyx mori |
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Authors: | Dedos Skarlatos G Wicher Dieter Kaltofen Sabine Birkenbeil Heiner |
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Institution: | Saxon Academy of Sciences at Leipzig, Department of Neurohormones, Jena, Germany. sd323@cam.ac.uk |
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Abstract: | 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. |
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