Tityustoxin-K(alpha) blockade of the voltage-gated potassium channel Kv1.3

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.