Interaction of δ-latroinsectotoxin from black widow spider venom with the plane phospholipid membrane

delta-Latroinsectotoxin (delta-LIT) isolated from black widow spider (Latrodectus mactans) venom caused step-like increase in ion conductance of bilayer lipid membranes (BLM) that suggests the formation of ionic channels in the matrix of lipid bilayer. The discrete increases in transmembrane current changed within the range of 1-30 pA. The most probable conductances of single delta-LIT channels at membrane potential of 100 mV were 195 pS and 30 pS in the solutions of 100 MM KCl and 10 MM CaCl2, respectively. The frequency of single channel formation in a symmetric solution of 10 MM CaCl2 did not depend on the membrane potential and was 5.5-0.5-fold higher than in a symmetric solution of 100 MM KCl. The steady increase in current was achieved in the solutions of monovalent cations (100 MM K+,100 MM Na+) at much larger toxin concentrations than in the solutions of divalent cations (10 MM Ca2+, 10 MM Mg-2). The ratio of inward (at 80 mV) and outward (at -80 mV) currents via delta-LIT channels increased twice for divalent cations (10 MM Ca2+, 10 MM Mg2+) compared to current of monovalent cations (100 MM K+, 100 MM Na+) that suggests the potential-dependence of delta-LIT channels and the polarized insertion of the toxin molecules into a membrane. The relative permeability of delta-LIT channels for Ca2+ was 2.7 times higher than the relative permeability for K+ compared to Cl-: PK+, = 1.83P(Cl-); PCa2+ = 5P(Cl-)_. The permeability of delta-LIT channels for mono- and divalent cations with respect of Ca2+ decreased in the order: Ba2+ > Ca2+ > Mg2+ > K+ > Na+ (Zn2+ H Cd2+ blocked the Ca2+-current by 70-80% with the ratio of Ca-trans(2+) and Cd-cis(2+) or Zn-cis(2+) of 1:1) that allows to suggest the preferable admittance of Ca2+ through delta-LIT channels compared to other physiologically significant cations. Comparative analysis of ion-conductive properties for delta-LIT and investigated earlier alpha-latrotoxin and alpha-latroinsectotoxin showed that the membrane insertion of all listed latrotoxins is being activated by divalent cations (Ca2+, Mg2+) and leads to the formation of potential-dependent channels that admit the current of physiologically significant cations with a weak preference for Ca2+.