title: Biochemical characterization of kappaM-RIIIJ, a Kv1.2 channel blocker: evaluation of cardioprotective effects of kappaM-conotoxins.
abstract: Conus snail (Conus) venoms are a valuable source of pharmacologically active compounds; some of the peptide toxin families from the snail venoms are known to interact with potassium channels. We report the purification, synthesis, and characterization of kappaM-conotoxin RIIIJ from the venom of a fish-hunting species, Conus radiatus. This conopeptide, like a previously characterized peptide in the same family, kappaM-RIIIK, inhibits the homotetrameric human Kv1.2 channels. When tested in Xenopus oocytes, kappaM-RIIIJ has an order of magnitude higher affinity (IC(50) = 33 nm) to Kv1.2 than kappaM-RIIIK (IC(50) = 352 nm). Chimeras of RIIIK and RIIIJ tested on the human Kv1.2 channels revealed that Lys-9 from kappaM-RIIIJ is a determinant of its higher potency against hKv1.2. However, when compared in a model of ischemia/reperfusion, kappaM-RIIIK (100 mug/kg of body weight), administered just before reperfusion, significantly reduces the infarct size in rat hearts in vivo without influencing hemodynamics, providing a potential compound for cardioprotective therapeutics. In contrast, kappaM-RIIIJ does not exert any detectable cardioprotective effect. kappaM-RIIIJ shows more potency for Kv1.2-Kv1.5 and Kv1.2-Kv1.6 heterodimers than kappaM-RIIIK, whereas the affinity of kappaM-RIIIK to Kv1.2-Kv1.7 heterodimeric channels is higher (IC(50) = 680 nm) than that of kappaM-RIIIJ (IC(50) = 3.15 mum). Thus, the cardioprotection seems to correlate to antagonism to heteromultimeric channels, involving the Kv1.2 alpha-subunit rather than antagonism to Kv1.2 homotetramers. Furthermore, kappaM-RIIIK and kappaM-RIIIJ provide a valuable set of probes for understanding the underlying mechanism of cardioprotection.
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, Utah 84112.
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.affiliation: Institute for Experimental and Clinical Pharmacology and Toxicology, Universitaetsklinikum Schleswig-Holstein, D-23538 Luebeck, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Dendorfer
authors.affiliation: Department of Physiology and Pharmacology and the Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada; Institute of Physiology, Christian-Albrechts-University Kiel, Olshausenstrasse 40, 24098 Kiel, Germany.
authors.forename: Rocio K
authors.initials: RK
authors.lastname: Finol-Urdaneta
authors.affiliation: Institute for Experimental and Clinical Pharmacology and Toxicology, Universitaetsklinikum Schleswig-Holstein, D-23538 Luebeck, Germany; Institute of Physiology, Christian-Albrechts-University Kiel, Olshausenstrasse 40, 24098 Kiel, Germany. Electronic address: h.terlau@physiologie.uni-kiel.de.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Terlau
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, Utah 84112.
authors.forename: Baldomero M
authors.initials: BM
authors.lastname: Olivera
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020916:Conotoxins / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D051663:Kv1.2 Potassium Channel / Q000037:antagonists & inhibitors*; D008297:Male; D008969:Molecular Sequence Data; D051381:Rats; D017208:Rats, Wistar; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D020916:Conotoxins; D051663:Kv1.2 Potassium Channel