{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,16]],"date-time":"2026-10-16T03:35:38Z","timestamp":1792121738924,"version":"4.4.0"},"reference-count":45,"publisher":"American Physiological Society","issue":"5","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Neurophysiology"],"published-print":{"date-parts":[[2003,11]]},"abstract":"<jats:p>Peptide channel blockers found in venoms of many predators are useful pharmacological tools and potential therapeutic agents. The venom of the Brazilian spider Phoneutria nigriventer contains a fraction, \u03c9-phonetoxin-IIA (\u03c9-Ptx-IIA, 8360 MW), which blocks Ca<jats:sup>2+<\/jats:sup>channels. At frog neuromuscular junctions (NMJ) bathed in normal Ca<jats:sup>2+<\/jats:sup>(1.8 mM) saline, \u03c9-Ptx IIA did not affect spontaneous transmitter release but reversibly reduced evoked transmitter release by 75 and 95% at 12 and 24 nM, respectively. In contrast, toxin effects were irreversible in low-Ca<jats:sup>2+<\/jats:sup>(0.5 mM) saline. Ca<jats:sup>2+<\/jats:sup>imaging in normal-Ca<jats:sup>2+<\/jats:sup>saline showed that \u03c9-Ptx-IIA partially blocked stimulus-dependent presynaptic Ca<jats:sup>2+<\/jats:sup>signals, and the blockade was almost completely reversible. Increases in spontaneous release frequency induced by high extracellular K<jats:sup>+<\/jats:sup>were blocked by \u03c9-Ptx-IIA. Therefore \u03c9-Ptx-IIA blocks N-type Ca<jats:sup>2+<\/jats:sup>channels, which admit Ca<jats:sup>2+<\/jats:sup>that triggers transmitter release at the frog NMJ. Additional evidence predicts that \u03c9-Ptx-IIA binds to N-type Ca<jats:sup>2+<\/jats:sup>channels at a different site from that of \u03c9-Conotoxin-GVIA. \u03c9-Ptx-IIA also gave a low-affinity partial blockade of transmitter release and presynaptic Ca<jats:sup>2+<\/jats:sup>signals at crayfish NMJs where P-type channels are blocked by \u03c9-agatoxin-IVA. The Ca<jats:sup>2+<\/jats:sup>-dependent reversibility and promiscuity of this toxin may make it highly useful experimentally and therapeutically.<\/jats:p>","DOI":"10.1152\/jn.00155.2003","type":"journal-article","created":{"date-parts":[[2006,5,31]],"date-time":"2006-05-31T06:01:10Z","timestamp":1149055270000},"page":"3529-3537","source":"Crossref","is-referenced-by-count":8,"title":["Promiscuous and Reversible Blocker of Presynaptic Calcium Channels in Frog and Crayfish Neuromuscular Junctions From<i>Phoneutria nigriventer<\/i>Spider Venom"],"prefix":"10.1152","volume":"90","author":[{"given":"Lanfranco R. 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