Pharmacological effects of calcium channel antagonists on juvenile hormone acid release and intracellular calcium level in the corpora allata of adult male Mythimna loreyi (Lepidoptera: Noctuidae)

The pharmacological effects of calcium channel antagonists on the in vitro release of juvenile hormone acids (JHAs) and the intracellular calcium concentration ([Ca 2 + ] i ) in corpora allata (CA) of Mythimna loreyi adult males were investigated in this study. Newly dissected CA were first incubated in medium 199 for 1 h for equilibration, CA were then transferred to fresh medium containing Ca 2 + channel antagonists for another 3-h incubation. Most antagonists of the voltage-dependent calcium channel (VDCC) subtypes ( L-. N-, P-, Q-, R-, and T-types), at physiological doses, were unable to inhibit JHA release, except for diazoxide. Among the non-specific calcium channel antagonists, cadmium (Cd 2 + ), cobalt (Co 2 + ), and lanthanum (La 3 + ) were effective inhibitors of JHA release. The effects of VDCC antagonists (i.e., diazoxide and verapamil) and non-specific calcium channel antagonists on [Ca 2 + ] i were also measured in individual CA cells with Fura-2. Excised glands were first loaded with 20 μM fura-2/AM in lep-idopteran saline for 45 min at 28°C in the dark. After hydrolysis, the [Ca 2 + ] i was observed for 30 min. Diazoxide (10 - 4 M) initially caused a significant depression of [Ca 2 + ] i , which then gradually increased to a normal level. Among the non-specific calcium channel antagonists, both Cd 2 + and La 3 + caused a significant depression of [Ca 2 + ] i . Our results suggest the possible existence of some kind of calcium channel in the plasma membrane of CA cells.