Selective block of Ca(2+)-dependent K+ current in crayfish neuromuscular system and chromaffin cells by sea anemone Bunodosoma cangicum venom.

The effects of the nematocyst venom of the sea anemone Bunodosoma cangicum on depolarization-activated currents were studies in opener crayfish muscle fibers and in cultured bovine chromaffin cells. The venom selectively and reversibly blocked the Ca(2+)-dependent K+ current (IK(Ca)) present in crayfish muscle in a dose-dependent manner without affecting voltage-gated Ca2+ or K+ currents. Furthermore, the venom also reduced IK(Ca) in chromaffin cells, without modifying voltage-gated Na+, Ca2+, or K+ currents. Synaptic transmission in crayfish muscle was also affected by the venom. Repetitive excitatory and inhibitory postsynaptic currents (each associated with a presynaptic action potential) were evoked by each nerve stimulus, suggesting that presynaptic IK(Ca) may control the electrical activity of excitatory and inhibitory presynaptic fibers. We conclude that B. cangicum venom includes a toxin that selectively and reversibly blocks Ca(2+)-dependent K+ currents in crayfish muscle and in bovine chromaffin cells, and modifies excitatory and inhibitory synaptic transmission, probably abolishing a similar conductance at the presynaptic fibers.