Manipulation of intracellular calcium affects in vitro juvenile hormone synthesis by larval corpora allata of Manduca sexta

Abstract

The effect of altering intracellular free Ca 2+ on juvenile hormone (JH) and acid synthesis by larval and pupally-committed corpora allata (CA) of fifth stadium Manduca sexta was investigated. Larval CA required extracellular Ca 2+ ≧ 0.1 mM for maximal JH synthesis, while JH acid synthesis by glands after pupal commitment was independent of extracellular Ca 2+. Free Ca 2+ in the hemolymph ranged from 1.4 to 2.1 mM during the fifth stadium. Both calcium ionophores and caffeine, which releases Ca 2+ from intracellular stores, inhibited JH synthesis by larval CA but stimulated JH acid synthesis by post-commitment CA. These results suggest that intracellular stores may be the principal source of Ca 2+ for the biosynthetic activity of the post-commitment gland. Calcium channel blockers (La 3+, Cd 2+) and antagonists (verapamil, isradipine and nitrendipine) decreased both JH and JH acid synthesis, indicating the existence of Ca 2+ channels in the CA cell membrane. Calmodulin (CaM) antagonists inhibited the activity of both larval and post-commitment CA, suggesting an integral relationship of CaM to the effects of Ca 2+ on gland activity. One of these effects is the demonstrated requirement of 0.1 mM extracellular Ca 2+ for allatostatin inhibition of JH I synthesis by larval CA.