EVIDENCE FOR CALCIUM CHANNELS INVOLVED IN REGULATING NEMATOCYST DISCHARGE

In the tentacles of sea anemones, nematocyst discharge is regulated by cnidocyte/supporting cell complexes (CSCCs) of which three functional types have been identified: A, B and C. Type A CSCCs respond to conta ct by vibrating targets. Types B and C CSCCs respond to contact by sta tic targets. Whereas type C CSCCs respond to contact alone, type B CSC Cs require that surface chemoreceptors bind ligands before becoming re sponsive. Reducing Ca2+levels in artificial seaw ater to below 1 mM in hibits discharge from each type of CSCC. The calcium channel inhibitor s, nifedipine or verapamil, selectively inhibit discharge from type B CSCCs. The calcium channel activator, Bay K-8644, mimics the biphasic dose response of type B CSCCs to natural chemosensitizers such as N-ac etylated sugars. Discharge from type A CSCCs is unaffected by inhibito rs of L-type calcium channels, but is selectively inhibited by the ami noglycoside antibiotics, gentamicin and streptomycin. While each type of CSCC requires extracellular calcium, the calcium channels employed may vary according to CSCC type.