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RH Scott, AC Dolphin, VP Bindokas and ME Adams
Department of Physiology, St. George's Hospital Medical School, London, United Kingdom.
Ca2+ channel currents were recorded from cultured rat dorsal root ganglion neurons and cerebellar granule cells using the whole-cell recording variant of the patch clamp technique. omega-Aga-IA, a toxin purified from the venom of the American funnel web spider, Agelenopsis aperta, markedly inhibited high threshold barium currents (lBa) when applied at 10 nM concentration. The low threshold T-type current activated at Vc = -30 mV and the outward (Ca2+ channel) current activated at +120 mV were significantly less sensitive to omega-Aga-IA, omega-Conotoxin GVIA (1 microM) inhibited IBa irreversibly. In contrast, the action of omega-Aga-IA was partially reversed 5 min after its removal. The voltage-activated calcium current (ICa) was inhibited by omega-Aga-IA in a manner different from IBa. ICa measured at the end of a 100-msec voltage step command was reduced to a greater extent than the peak current. The residual ICa following application of omega-Aga- IA was a fast transient current. omega-Aga-IA did not inhibit voltage- activated sodium currents from dorsal root ganglion neurons in the absence of tetrodotoxin. omega-Aga-IA abolished the dihydropyridine (+)- 202-791-sensitive L-type current component of IBa. We conclude that omega-Aga-IA is a very potent inhibitor of neuronal voltage-activated Ca2+ channel currents and that it may prove to be a useful tool in the characterization and isolation of Ca2+ channels.
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