title: omega-Grammotoxin blocks action-potential-induced Ca2+ influx and whole-cell Ca2+ current in rat dorsal-root ganglion neurons.
abstract: Field-potential stimulation of rat dorsal-root ganglion (DRG) neurons evoked action-potential-mediated transient increases in intracellular free calcium concentration ([Ca2+]i) as measured by indo-1-based microfluorimetry. Field-potential-evoked [Ca2+]i transients were abolished by tetrodotoxin, and their dependence on stimulus intensity exhibited an abrupt threshold. omega-Conotoxin GVIA (omega-CgTx, 100 nM) inhibited action-potential-mediated Ca2+ influx by 79%, while nitrendipine (1 microM) had little effect. omega-Grammotoxin SIA (omega-GsTx, 267 nM), a peptide toxin purified from the venom of the tarantula spider, Grammostola spatulata, blocked action-potential-mediated Ca2+ influx as effectively as did omega-CgTx, suggesting that omega-GsTx blocks N-type Ca2+ channels. In contrast to block by omega-CgTx, the block produced by omega-GsTx reversed upon washout of the peptide. omega-GsTx (270 nM) blocked 80%, and omega-CgTx (1 microM) blocked 64%, of whole-cell Ca2+ current (ICa) elicited by step depolarization to 0 mV from a holding potential of -80 mV. omega-GsTx completely occluded inhibition of ICa by omega-CgTx. However, when applied after omega-CgTx, omega-GsTx produced an additional inhibition of 27%, indicating that omega-GsTx also blocked a non-N-type Ca2+ channel. BayK8644 (1 microM) elicited an increase in ICa in the presence of maximally effective concentrations of omega-GsTx, suggesting that omega-GsTx does not block L-type channels. Thus, omega-GsTx displays a selectivity for Ca2+ channel subtypes which should prove useful for studying Ca2+ channels and Ca(2+)-channel-mediated processes.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis 55455.
authors.forename: T M
authors.initials: TM
authors.lastname: Piser
authors.forename: R A
authors.initials: RA
authors.lastname: Lampe
authors.forename: R A
authors.initials: RA
authors.lastname: Keith
authors.forename: S A
authors.initials: SA
authors.lastname: Thayer
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005434:Flow Cytometry; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009568:Nitrendipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013111:Spider Venoms / Q000494:pharmacology*; D020866:omega-Conotoxin GVIA
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D010456:Peptides, Cyclic; D013111:Spider Venoms; C082807:omega-grammotoxin SIA; D020866:omega-Conotoxin GVIA; D009568:Nitrendipine; D002118:Calcium