Antibodies against Tityus discrepans venom do not abolish the eect of Tityus serrulatus venom on the rat sodium and potassium channels Adolfo Borges a, *, Robert G. Tsushima b , Peter H. Backx b a Departamento de BiologõÂa Celular, Universidad Simo Ân BolõÂvar, Sartenejas, Apartado Postal 89000, Caracas 1080-A, Venezuela b Departments of Medicine and Physiology, University of Toronto, Toronto, Ont., Canada M5G 2C4 Received 14 April 1998; accepted 28 August 1998 Abstract Anti-(Tityus serrulatus + Tityus bahiensis) and anti-Tityus discrepans venom polyclonal antisera were used to investigate whether antigenic dierences exist between the venoms of the Brazilian T. serrulatus and the Venezuelan T. discrepans scorpions. Both antisera recognised the toxin-containing electrophoretic fractions of their cognate venoms and also those from Tityus zulianus and Tityus trinitatis venoms on Western blots. The anti-T. discrepans antiserum reacted only weakly with T. serrulatus toxic polypeptides. The eect of T. serrulatus a- or b-toxins on rat skeletal muscle Na + channels expressed in Xenopus laevis oocytes was abolished by pre-incubating the venom with anti-(T. serrulatus + T. bahiensis) serum but not with anti-T. discrepans serum. Nor did the Brazilian or the Venezuelan sera prevent the reduction in K + currents by T. serrulatus venom in X. laevis oocytes expressing the rat brain delayed rectifying Shaker K + channel (Kv1.2). These results indicate that toxins from T. serrulatus and T. discrepans venoms, which primarily target mammalian Na + channels, are antigenically distinct, although they probably share common epitopes. Our results also suggest that Na + channel-active toxins are the immunodominant antigens of the T. serrulatus venom. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Scorpion; Antivenom; Tityus Toxicon 37 (1999) 867±881 0041-0101/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0041-0101(98)00201-3 PERGAMON * Corresponding author. Toronto General Hospital, 101 College Street, CCRW 3-806, Toronto, Ont., Canada M56 2C4. Fax: +1-416-340-4596; E-mail: aborges@mailexcite.com