Three novel peptides with the ability to inhibit voltage-dependent potassium channels in the shab (Kv2) and shal (Kv4) subfamilies were identified from the venom of the African tarantulas Stromatopelma calceata (ScTx1) and Heteroscodra maculata (HmTx1, HmTx2). The three toxins are 34-to 38-amino acid peptides that belong to the structural family of inhibitor cystine knot spider peptides reticulated by three disulfide bridges. Electrophysiological recordings in COS cells show that these toxins act as gating modifier of voltage-dependent K ϩ channels. ScTx1 is the first high-affinity inhibitor of the Kv2.2 channel subtype (IC 50 , 21.4 nM) to be described. ScTx1 also inhibits the Kv2.1 channels, with an IC 50 of 12.7 nM, and Kv2.1/Kv9.3 heteromultimers that have been proposed to be involved in O 2 sensing in pulmonary artery myocytes. In addition, it is the most effective inhibitor of Kv4.2 channels described thus far, with an IC 50 of 1.2 nM. HmTx toxins share sequence similarities with both the potassium channel blocker toxins (HmTx1) and the calcium channel blocker toxin -GsTx

SUMMARYThe effect of haemoparasites on the physiology and behaviour traits of their hosts was examined using Haemogregarina sp., a parasite of the common lizard, Lacerta vivipara, from the south of France. Infection with haemogregarines was associated with a reduced haemoglobin concentration and an increased number of immature red blood cells. Parasitized individuals also showed a reduced oxygen consumption at rest and a lower locomotor speed. We also found that the multiplication rate of the parasite depended on the temperature at which the lizard was maintained. Between 21 and 28 °C the multiplication rate of the parasite was significantly lower than between 29 and 35 °C. This suggests that the parasites may suffer reproductive costs when hosts reduce their body temperature.

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Two novel peptides that inhibit the intra-erythrocyte stage of Plasmodium falciparum in vitro were identified in the venom of the Trinidad chevron tarantula, Psalmopoeus cambridgei. Psalmopeotoxin I (PcFK1) is a 33-residue peptide and Psalmopeotoxin II (PcFK2) has 28-amino acid residues; both have three disulfide bridges and belong to the Inhibitor Cystine Knot superfamily. The cDNAs encoding both peptides were cloned, and nucleotide sequence analysis showed that the peptides are synthesized with typical signal peptides and pro-sequences that are cleaved at a basic doublet before secretion of the mature peptides. The IC(5O) of PcFK1 for inhibiting P. falciparum growth was 1.59+/-1.15 microM and that of PcFK2 was 1.15+/-0.95 microM. PcFK1 was adsorbed strongly to uninfected erythrocytes, but PcFK2 was not. Neither peptide has significant hemolytic activity at 10 microM. Electrophysiological recordings in isolated frog and mouse neuromuscular preparations revealed that the peptides (at up to 9.3 microM) do not affect neuromuscular transmission or quantal transmitter release. PcFK1 and PcFK2 do not affect the growth or viability of human epithelial cells, nor do they have any antifungal or antibacterial activity at 20 microM. Thus, PcFK1 and PcFK2 seem to interact specifically with infected erythrocytes. They could therefore be promising tools for antimalaria research and be the basis for the rational development of antimalarial drugs.