Voltage-dependent calcium channels in the corpora allata of the adult male loreyi leafworm, Mythimna loreyi

In the corpora allata (CA) of the adult male loreyi leafworm, Mythimna loreyi, juvenile hormone acid (JHA) biosynthesis and release show a dose dependence on extracellular Ca(2+) concentration. Maxima are obtained with Ca(2+) concentrations of 2-10 mM, and synthesis and release are significantly inhibited under a Ca(2+)-free condition. The Ca(2+)-free inhibition of JHA release can be reversed by returning the glands to medium at 5 mM Ca(2+). The cytosolic free Ca(2+) concentration (Ca(2+)](i)), which was measured with fura-2, in individual CA cells also shows a dose dependence on extracellular Ca(2+) concentration, with significant Ca(2+)](i) depression being observed in the absence of extracellular Ca(2+).High K(+) significantly increases the JHA release and causes a transient Ca(2+)](i) increase within seconds in CA cells. High-K(+)-stimulated JHA release is partially inhibited by the benzothiazepine (BTZ)-, dihydropyridine (DHP)- and phenylalkylamine (PAA)-sensitive L-type voltage-dependent calcium channel (VDCC) antagonists diltiazem, nifedipine and verapamil, respectively; by the N- and P/Q-type VDCC antagonist omega-conotoxin (omega-CgTx) MVIIC; and by the T-type VDCC antagonist amiloride. The N-type antagonist omega-CgTx GVIA is the most potent in inhibiting the high-K(+)-stimulated JHA release. No inhibitory effect is shown by the P-type antagonist omega-agatoxin TK (omega-Aga TK). The high-K(+)-induced transient Ca(2+)](i) increase is largely inhibited by the L-type antagonists (diltiazem, nifedipine, verapamil), by the N- and P/Q-type antagonist omega-CgTx MVIIC and by the T-type antagonist amiloride, and is totally inhibited by the N-type antagonist omega-CgTx GVIA. No inhibitory effect is shown by the P-type antagonist omega-Aga TK.We hypothesize that L-type, N-type and T-type VDCCs may be involved to different degrees in the high-K(+)-stimulated JHA release and transient Ca(2+)](i) increase in the individual CA cells of the adult male M. loreyi, and that the N-type VDCCs may play important roles in these cellular events.