PHARMACOLOGICAL CHARACTERIZATION OF Bunodosoma TOXINS ON MAMMALIAN VOLTAGE DEPENDENT SODIUM CHANNELS.

Summary Voltage dependent sodium channels represent an important target for different neurotoxins and there have been identified different binding sites according to these interactions. The so called site 3 toxins comprise a diverse group of peptides obtained from sea anemones and α-scorpions that bind to voltage gated sodium channels slowing down the inactivation process. These polypeptides vary considerably in their affinities for the sodium channels in different excitable cells. In this work we studied the pharmacological action of three toxins: BcIII (isolated from Bunodosoma caissarum), BgII and BgIII (isolated from Bunodosoma granulifera) on isolated cultured neurons of rat dorsal root ganglia. The biophysical effects and the potency of these polypeptides were compared and their effects were studied using whole cell patch clamp techniques. These compounds considerably prolonged the action potential and selectively slowed down the inactivation process of tetrodotoxin-sensitive (TTX-S) sodium current. The potency of these compounds according to the IC50 values was of: BcIII 2.7 ± 2 µM, BgII 4.1 ± 1.2 µM and BgIII 11.9 ± 1.4 µM. These differences could be determined for the slight variations in the amino acid composition of these peptides and the contribution of specific amino acids in the binding to the sodium channel.