Effects of potassium channel toxins from Leiurus quinquestriatus hebraeus venom on responses to cromakalim in rabbit blood vessels

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Abstract
1 The effects of fractionated Leiurus quinquestriatus hebraeus venom on cromakalim-induced 86Rb+ efflux in rabbit aortic smooth muscle were examined. 2 Crude venom (0.1–30 μg ml−1) produced a concentration-dependent decrease of 1 μm cromakalim-induced 86Rb+ response. The maximum blocking activity attainable was approximately 60%. 3 Fractionation of crude venom by gel permeation chromatography and subsequent chromatography on a cation ion-exchange column, produced two fractions (X and XI), active in the 86Rb+ blocking assay. 4 Fraction XII contained charybdotoxin (∼85% pure). After a final high performance liquid chromatography (h.p.l.c.) purification step, the purified toxin failed to inhibit the cromakalim-stimulated 86Rb+ efflux although it was a potent inhibitor of A23187-induced K+ flux in human erythrocytes and the large conductance calcium-activated potassium channel in rabbit portal vein smooth muscle. 5 Subsequent purification of fraction X by h.p.l.c. yielded a minor peak which contained 86Rb+ blocking activity. This subfraction was also capable of inhibiting apamin-sensitive, angiotensin II-stimulated K+ flux in guinea-pig hepatocytes. 6 It is concluded that the potassium channel opened by cromakalim in rabbit aortic smooth muscle is not blocked by charybdotoxin but by another distinct toxin in the venom of Leiurus quinquestriatus hebraeus.