Novel Wasp Toxin Discriminates between Neuronal and Cardiac Sodium Channels

Abstract

Pompilidotoxins (PMTXs), derived from the venom of solitary wasp has been known to facilitate synaptic transmission in the lobster neuromuscular junction, and a recent further study from rat trigeminal neurons revealed that the toxin slows Na+ channel inactivation without modifying activation process. Here we report that beta-PMTX modifies rat brain type II Na+ channel alpha-subunit (rBII) expressed in human embryonic kidney cells but fails to act on the rat heart alpha-subunit (rH1) at similar concentrations. We constructed a series of chimeric mutants of rBII and rH1 Na+ channels and compared modification of the steady-state Na+ currents by beta-PMTX. We found that a difference in a single amino acid between Glu-1616 in rBII and Gln-1615 in rH1 at the extracellular loop of D4S3-S4 is crucial for the action of beta-PMTX. PMTXs, which are small peptides with 13 amino acids, would be a potential tool for exploring a new functional moiety of Na+ channels.

Production of Resurgent Current in NaV1.6-Null Purkinje Neurons by Slowing Sodium Channel Inactivation with β-Pompilidotoxin

“…In all three cell types, ␤-PMTX had small but consistent effects on the parameters of activation, summarized in Table 1. Consistent with studies in expression systems (Kinoshita et al, 2001), application of 10 M ␤-PMTX to dissociated neurons slowed the rate of inactivation of transient sodium currents and enhanced steady-state currents, although the extent of these effects differed across the three classes of cells. In wild-type Purkinje cells, ␤-PMTX modestly but significantly increased the decay time constant ( decay ) of currents evoked by a step from Ϫ90 to 0 mV from 0.52 Ϯ 0.01 to 0.73 Ϯ 0.05 msec (n ϭ 10; p Ͻ 0.01) ( Fig.…”

“…Because the accessibility of this site is likely to increase at depolarized potentials (Jiang et al, 2003), the I ss /I peak in ␤-PMTX is expected to increase with voltage, predicting a positive slope to the plot of I ss /I peak versus voltage. The ␤-PMTX-modified sodium currents of CA3 cells, like expressed Na V 1.2 channels (Kinoshita et al, 2001), conformed to this pattern of voltage dependence. I ss /I peak became larger at more positive potentials, increasing the slope of the fit to the data fivefold (to 0.15 Ϯ 0.03% per millivolt; p ϭ 0.04) (Fig.…”

“…Previous studies have shown that the binding site of ␤-PMTX is located on the S3-S4 linker of domain IV of sodium channel ␣ subunits (Kinoshita et al, 2001). Because the accessibility of this site is likely to increase at depolarized potentials (Jiang et al, 2003), the I ss /I peak in ␤-PMTX is expected to increase with voltage, predicting a positive slope to the plot of I ss /I peak versus voltage.…”

“…In these experiments, by slowing conventional inactivation with the wasp venom ␤-pompilidotoxin (␤-PMTX) (Kinoshita et al, 2001), we tested whether the rate of conventional inactivation significantly influences the susceptibility of nonNa V 1.6 subunits to open-channel block. We also explored whether Purkinje neurons retain a functional blocker even in the absence of Na V 1.6.…”

Relative Contributions of Axonal and Somatic Na Channels to Action Potential Initiation in Cerebellar Purkinje Neurons

“…We therefore tested the effect of increasing perisomatic or axonal Na channel availability with ␤-PMTX, which destabilizes fast inactivated states of Na channels (Kinoshita et al, 2001). In classical Na channels, the reduction of fast inactivation increases persistent current, whereas in Na channels with resurgent kinetics, it enlarges resurgent current (Grieco and Raman, 2004).…”