INHIBITORY ACTIONS OF SYNTHESIZED POLYAMINE SPIDER TOXINS AND THEIR ANALOGS ON NEURONAL VOLTAGE-ACTIVATED CALCIUM CURRENTS

The whole cell variant of the patch clamp technique was used to invest igate the actions of polyamine spider toxins and their analogues on hi gh voltage-activated Ca2+ currents. The actions of synthesised FTX (pu tative natural toxin from the American funnel web spider), sFTX-3.3, O rn-FTX-3.3 and Lys-FTX-3.3 (synthetic analogues of FTX) were studied u sing cultured dorsal root ganglion neurones from neonatal rats, C2D7 c ells (HEK293 cells stably coexpressing recombinant human N-type voltag e-activated Ca2+ channel, alpha 1B-1-alpha(2b)delta beta(1b) subunits) and freshly isolated cerebellar Purkinje neurones. In dorsal root gan glion neurones, sFTX-3.3 (10 mu M) inhibited high voltage-activated Ca 2+ currents evoked by depolarisations to 0 mV from a holding potential of -90 mV. Partial overlap in Ca2+ current sensitivity to the polyami ne sFTX-3.3 and the peptide spider toxin omega-Aga IVA was observed. H owever, evidence also suggests sFTX-3.3 and omega-Aga IVA do not show complete pharmacological overlap and that distinct parts of the Ca2+ c urrent are sensitive to one of two inhibitors. The arginine group on s FTX-3.3 appears to be important for its inhibitory action on Ca2+ curr ents, because analogues where this amino acid was replaced with either ornithine (Orn-FTX-3.3) or lysine (Lys-FTX-3.3) were relatively inact ive at concentrations below 1 mM. Synthesised FTX (100 mu M) was inact ive as an inhibitor of Ca2+ currents recorded from dorsal root ganglio n and only produced modest effects in Purkinje neurones and C2D7 cells . At a concentration of 1 mM, nonselective actions were observed that indicated that synthesised FTX and sFTX-3.3 could reversibly inhibit b oth N- and P-type Ca2+ channels equally well. In conclusion, the poten cy of polyamines as nonselective inhibitors of Ca2+ channels is in par t determined by the presence of a terminal arginine, and this may invo lve an interaction between terminal guanidino groups with Ca2+ binding sites. Copyright (C) 1997 Elsevier Science Inc.