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+.
Tibbs
G R
GR
Department of Biochemistry, Imperial College of Science and Technology, London, England.
Nicholls
D G
DG
Dolly
J O
JO
D000818:Animals; D001030:Apamin / Q000494:pharmacology*; D001514:Bee Venoms / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D018999:Charybdotoxin; D003600:Cytosol / Q000187:drug effects* / Q000378:metabolism; D004357:Drug Synergism; D004546:Elapid Venoms / Q000494:pharmacology*; D004553:Electric Conductivity; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D012604:Scorpion Venoms / Q000494:pharmacology*; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism
D001514:Bee Venoms; D004546:Elapid Venoms; D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin; D001030:Apamin; C020273:dendrotoxin; D002118:Calcium