title: Inhibition of high voltage-activated calcium channels by spider toxin PnTx3-6.
abstract: Animal peptide toxins have become powerful tools to study structure-function relationships and physiological roles of voltage-activated Ca(2+) channels. In the present study, we investigated the effects of PnTx3-6, a neurotoxin purified from the venom of the spider Phoneutria nigriventer on cloned mammalian Ca(2+) channels expressed in human embryonic kidney 293 cells and endogenous Ca(2+) channels in N18 neuroblastoma cells. Whole-cell patch-clamp measurements indicate that PnTx3-6 reversibly inhibited L-(alpha(1C)/Ca(v)1.2), N-(alpha(1B)/Ca(v)2.2), P/Q-(alpha(1A)/Ca(v)2.1), and R-(alpha(1E)/Ca(v)2.3) type channels with varying potency (alpha(1B) > alpha(1E) > alpha(1A) > alpha(1C)) and IC(50) values of 122, 136, 263, and 607 nM, respectively. Inhibition occurred without alteration of the kinetics or the voltage dependence of the exogenously expressed Ca(2+) channels. In N18 cells, PnTx3-6 exhibited highest potency against N-type (conotoxin-GVIA-sensitive) current. In contrast to its effects on high voltage-activated Ca(2+) channels subtypes, application of 1 microM PnTx3-6 did not affect alpha(1G)/Ca(v)3.1 T-type Ca(2+) channels. Based on our study, we suggest that PnTx3-6 acts as a omega-toxin that targets high voltage-activated Ca(2+) channels, with a preference for the Ca(v)2 subfamily (N-, P/Q-, and R-types).
authors.affiliation: Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
authors.forename: Luciene B
authors.initials: LB
authors.lastname: Vieira
authors.forename: Christopher
authors.initials: C
authors.lastname: Kushmerick
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hildebrand
authors.forename: Esperanza
authors.initials: E
authors.lastname: Garcia
authors.forename: Antony
authors.initials: A
authors.lastname: Stea
authors.forename: Marta N
authors.initials: MN
authors.lastname: Cordeiro
authors.forename: Michael
authors.initials: M
authors.lastname: Richardson
authors.forename: Marcus Vinicius
authors.initials: MV
authors.lastname: Gomez
authors.forename: Terrance P
authors.initials: TP
authors.lastname: Snutch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020864:Calcium Channels, N-Type / Q000187:drug effects; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D009498:Neurotoxins / Q000494:pharmacology*; D013111:Spider Venoms / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D009479:Neuropeptides; D009498:Neurotoxins; D013111:Spider Venoms; C098736:Tx3 neurotoxin