Dendrotoxin and charybdotoxin increase the cytosolic concentration of free Ca2+ in cerebrocortical synaptosomes: an effect not shared by apamin.

Nanomolar concentrations of charybdotoxin or dendrotoxin increase the cytoplasmic free Ca2+ concentration in isolated central nerve terminals. The effects of the two toxins, normally considered to be blockers of K+ channels controlled by voltage in a Ca2+-sensitive or -insensitive manner, respectively, show only marginal additivity. Apamin, and inhibitor of low conductance Ca2+-activated K+ channels, was without effect in either the absence or presence of dendrotoxin. The effect of charybdotoxin on polarized, isolated central nerve terminals seems to be mediated largely by a block of K+ channels sensitive to dendrotoxin. Apparently, these voltage-operated K+ channels make a more significant contribution to maintaining the polarized potential of synaptosomes than do those activated by Ca2+.