Pore-blocking toxins are valuable probes of ion channels that underlie electrical signaling. To be effective inhibitors, they must show high affinity and specificity and prevent ion conduction. The 22-residue sea snail peptide, mu-conotoxin GIIIA, blocks the skeletal muscle sodium channel completely. Partially blocking peptides, derived by making single or paired amino acid substitutions in mu-...

The effects of a neurotoxin, purified from the venom of the scorpion Leiurus quinquestriatus, on the ionic currents of toad single myelinated fibers were studied under voltage-clamp conditions. Unlike previous investigations using crude scorpion venom, purified Leiurus toxin II alpha at high concentrations (200-400 nM) did not affect the K currents, nor did it reduce the peak Na current in the ...

The effects of a neurotoxin, purified from the venom of the scorpion Leiurus quinquestriatus, on the ionic currents of toad single myelinated fibers were studied under voltage-clamp conditions . Unlike previous investigations using crude scorpion venom, purified Leiurus toxin IIa at high concentrations (200-400 nM) did not affect the K currents, nor did it reduce the peak Na current in the earl...

The effects of a neurotoxin, purified from the venom of the scorpion Leiurus quinquestriatus, on the ionic currents of toad single myelinated fibers were studied under voltage-clamp conditions . Unlike previous investigations using crude scorpion venom, purified Leiurus toxin IIa at high concentrations (200-400 nM) did not affect the K currents, nor did it reduce the peak Na current in the earl...

Remarkable activity-dependence was uncovered in the chloride conductance that operates in the subthreshold region of membrane potential, by using the twomicroelectrode voltage-clamp technique in the mature and intact rat sympathetic neuron. Both direct and synaptic neuron tetanization (15 Hz, 10 s duration to saturate the response) resulted in a long-lasting (not less than 15 min) increase of c...

Cyclic AMP- (cAMP) and calcium-dependent agonists stimulate chloride secretion through the coordinated activation of distinct apical and basolateral membrane channels and ion transporters in mucosal epithelial cells. Defects in the regulation of Cl- transport across mucosal surfaces occur with cystic fibrosis and V. cholerae infection and can be life threatening. Here we report that secramine B...

KP4 is a virally encoded fungal toxin secreted by the P4 killer strain of Ustilago maydis. Previous studies demonstrated that this toxin inhibits growth of the target fungal cells by blocking calcium uptake rather than forming channels, as had been suggested previously. Unexpectedly, this toxin was also shown to inhibit voltage-gated calcium channel activity in mammalian cells. We used whole-ce...

Goniopora toxin (GPT), a polypeptide toxin of 9700 Da isolated from coral, markedly slows inactivation of sodium currents recorded under voltage clamp in mouse neuroblastoma cells. The voltage dependence of sodium channel activation is shifted to more negative membrane potentials by 9.8 +/- 2.1 mV, and the voltage dependence of channel inactivation is shifted to more positive membrane potential...

The involvement of chloride in salt stress symptoms and salt tolerance mechanisms in plants has been less investigated in the past. Therefore, we studied the salt-induced chloride influx in Arabidopsis expressing the GFP-based anion indicator Clomeleon. High salt concentrations induce two phases of chloride influx. The fast kinetic phase is likely caused by membrane depolarization, and is assum...

A toxin from the scorpion Tityus serrulatus (TsTX-Kalpha) blocks native squid K(+) channels and their cloned counterpart, sqKv1A, at pH 8 ((native)K(d) approximately 20 nM; (sqKv1A)K(d) approximately 10 nM). In both cases, decreasing the pH below 7.0 significantly diminishes the TsTX-Kalpha effect (pK = 6.6). In the cloned squid channel, the pH dependence of the block is abolished by a single p...