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 contact by vibrating targets. Types B and C CSCCs respond to contact by static targets. Whereas type C CSCCs respond to contact alone, type B CSCCs require that surface chemoreceptors bind ligands before becoming responsive. Reducing Ca²⁺ levels in artificial seawater to below 1 mM inhibits discharge from each type of CSCC. The calcium channel inhibitors, 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-acetylated sugars. Discharge from type A CSCCs is unaffected by inhibitors of L-type calcium channels, but is selectively inhibited by the aminoglycoside antibiotics, gentamicin and streptomycin. While each type of CSCC requires extracellular calcium, the calcium channels employed may vary according to CSCC type.