title: Tityustoxin-K(alpha) blockade of the voltage-gated potassium channel Kv1.3.
abstract: 1. We investigated the action of TsTX-Kalpha on cloned Kv1.3 channels of the Shaker subfamily of voltage-gated potassium channels, using the voltage-clamp technique. Highly purified TsTX-Kalpha was obtained from the venom of the Brazilian scorpion Tityus serrulatus using a new purification protocol. Our results show that TsTX-Kalpha blocks Kv1.3 with high affinity in two expression systems. 2. TsTX-Kalpha blockade of Kv1.3 channels expressed in Xenopus oocytes was found to be completely reversible and to exhibit a pH dependence. The K(D) was 3.9 nM at pH 7.5, 9.5 nM at pH 7.0 and 94.5 nM at pH 6.5. 3. The blocking properties of TsTX-Kalpha in a mammalian cell line (L929), stably transfected to express Kv1.3, were studied using the patch-clamp technique. In this preparation, the toxin had a K(D) of 19.8 nM at pH 7.4. 4. TsTX-Kalpha was found to affect neither the voltage-dependence of activation, nor the activation and deactivation time constants. The block appeared to be independent of the transmembrane voltage and the toxin did not interfere with the C-type inactivation process. 5. Taken as a whole, our findings indicate that TsTX-Kalpha acts as a simple blocker of Kv1.3 channels. It is concluded that this toxin is a useful tool for probing not only the physiological roles of Kv1.2, but also those mediated by Kv1.3 channels.
authors.affiliation: Department of Physiology, Faculty of Medicine of Ribeirão Preto, USP, Av. Bandeirantes 3900, 14049-900 Ribeirão Preto, SP, Brazil. rogelis@physiology.wisc.edu
authors.forename: Aldo Rogelis A
authors.initials: AR
authors.lastname: Rodrigues
authors.forename: Eliane C
authors.initials: EC
authors.lastname: Arantes
authors.forename: Francisco
authors.initials: F
authors.lastname: Monje
authors.forename: Walter
authors.initials: W
authors.lastname: Stühmer
authors.forename: Wamberto Antonio
authors.initials: WA
authors.lastname: Varanda
mesh_terms: D000818:Animals; D005260:Female; D051664:Kv1.3 Potassium Channel; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D012604:Scorpion Venoms / Q000494:pharmacology*; D014981:Xenopus
chemical_list: C496974:Kcna3 protein, mouse; D051664:Kv1.3 Potassium Channel; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D012604:Scorpion Venoms; C003609:tityustoxin