VENOM AND TOXINS FROM ARGIOPE LOBATA: ELECTROPHYSIOLOGICAL STUDIES

Abstract

The purpose of this study was to present experimental data on the action of venom and toxins from Argiope lobata spiders on the glutamate channel-receptor complex. Kainate was used as a glutamate channel-receptor complex agonist because it initiated non-inactivated inward ionic transmembrane electric currents in rat hippocampal membranes. Effects of antagonists can be studied on the background of such currents. Chemo-activated currents and glutamate channel-receptor complex antagonists from A. lobata were studied. Electrophysiological experiments were performed and all chemicals were applied to perfused hippocampal pyramidal neuronal membranes using the ’concentration-clamp’ technique. A conventional electronic circuit was used for single-electrode voltage-clamp recording. All substances under study – integral venom, argiopin, argiopinine 1, argiopinine 2 – demonstrated similar properties. The amplitudes of ionic currents activated by glutamate, kainate and quisqualate decreased after the application of these antagonists to the rat hippocampal membrane under the voltage-clamp conditions. The kinetics of currents’ activation and desensitization (in case of glutamate and quisqualate) were not affected by the antagonists. The effects of argiopin and integral venom were investigated within the concentrations of 5^.10^-8–1^.10^-2 mol/L and 10^-4 g/mL, respectively. At these concentrations, neither integral venom, nor argiopin suppressed glutamate-, kainate-, quisqualate-activated currents completely. The amplitude of non-blocked integral venom components averaged 14.4% of the original value for kainate-activated currents. Argiopin reduced the amplitudes of kainate-activated currents to 19% of the control values. Argiopinine 1 and argiopinine 2 acted in a very similar way. Both substances caused reducing of glutamate- and kainate-activated ion currents amplitudes acting in small quantities of 10^-5–10^-6 mol/L. The differences between them were in the quantitative characteristics of the blocking action. Such effects as “dose–effect” dependency, the antagonists’ influences on activated and inactivated receptor; kinetics of the antagonists’ action and their removal, analysis of dissociation constants were studied under the antagonists’ influence. Conclusions about the mechanisms of the antagonists’ influence on glutamate channel-receptor complex, as well as a comparison of the caused effects were made.