Inhibition of neuronal high-voltage activated calcium channels by the omega-Phoneutria nigriventer Tx3-3 peptide toxin

We have investigated the effect of omega-PnTx3-3 (referred to in previous p apers simply as Tx3-3), a peptide toxin from the venom of the spider Phoneu tria nigriventer, on neuronal high-voltage activated (HVA) Ca2+ channels, u sing whole-cell patch-clamp. omega-PnTx3-3 (120 nM) blocked 74+/-8% of the total HVA Ca2+ currents of cerebellar granule neurones, without affecting t he low-voltage activated (LVA) current. P/Q/R-type currents in cerebellar g ranule neurones, isolated using 4 mu M nicardipine and 100 nM omega-conotox in GVIA, were markedly (79+/-6%) inhibited by 60 nM omega-PnTx3-3. R-type c urrents, isolated either by additional application of 0.5-1 mu M of omega-a gatoxin IVA or by pre-incubation with 5 mu M omega-conotoxin MVIIC were inh ibited almost totally by 120 nM of omega-PnTx3-3. omega-PnTx3-3 reversibly altered the kinetics of the P/Q/R current, increasing the degree of inactiv ation that occurred during a 50 ms pulse from 20% to 40%. N-type currents, recorded from neuroblastoma N18 cells, were partially (34+/-2%) inhibited b y 320 nM omega-PnTx3-3. L-type currents, recorded from GH3 cells, were part ially (45+/-12%) inhibited by 80 nM omega-PnTx3-3. We conclude that w-PnTx3 -3 inhibits all known HVA Ca2+ channels, and most effectively the P/Q- and R-type currents. (C) 2000 Elsevier Science Ltd. All rights reserved.