Protein kinase A and C are “Gatekeepers” of capacitative Ca2+ entry in the prothoracic gland cells of the silkworm, Bombyx mori

Application of protein kinases A and C inhibitors to the prothoracic glands cells of the silkworm, Bombyx mori, resulted in slow and gradual increases in intracellular Ca2+ ([Ca2+]i). Pharmacological manipulation of the Ca2+ signalling cascades in the prothoracic gland cells of B. mori suggests that these increases of [Ca2+]i are mediated neither by voltage-gated Ca2+ channels nor by intracellular Ca2+ stores. Rather they result from slow Ca2+ leak from plasma membrane Ca2+ channels that are sensitive to agents that inhibit capacitative Ca2+ entry and are abolished in the absence of extracellular Ca2+. Okadaic acid, an inhibitor of PP1 and PP2A phosphatases, blocked the increase in [Ca2+]i produced by the inhibitors of protein kinase A and C. The combined results indicate that the capacitative Ca2+ entry channels in prothoracic gland cells of B. mori are probably modulated by protein kinases A and C.