A new peptide toxin exhibiting a molecular weight of 5043 Da (av.) and comprising 47 amino acid residues was isolated from the sea anemone Condylactis gigantea. Purification of the peptide was achieved by a multistep chromatographic procedure monitoring its strong paralytic activity on crustacea (LD50 approx. 1 mu g/kg). Complete sequence analysis of the toxic peptide revealed the isolation of a new member of type I sea anemone sodium channel toxins containing the typical pattern of the six cysteine residues. From 11 kg of wet starting material, approximately 1 g of the peptide toxin was isolated. The physiological action of the new toxin from C. g qantea CgNa was investigated on sodium currents of rat dorsal root ganglion neurons in culture using whole-cell patch clamp technique (n = 60). Under current clamp condition (CgNa) increased action potential duration. This effect is due to slowing down of the TTX-S sodium current inactivation, without modifying the activation process. CgNa prolonged the cardiac action potential duration and enhanced contractile force albeit at 100-fold higher concentrations than the Anemonia sulcata toxin ATXII. The action on sodium channel inactivation and on cardiac excitation-contraction coupling resemble previous results with compounds obtained from this and other sea anemones [Shapiro, B.I, 1968. Purification of a toxin from tentacles of the anemone C gigantea. Toxicon 5, 253-259; Pelhate, M., Zlotkin, E., 1982. Actions of insect toxin and other toxins derived from the venom of scorpion Androtonus australis on isolated giant axons of the cockroach Periplaneta americana. J. Exp. Biol. 97, 67-77; Salgado, V., Kern, W., 1992. Actions of three structurally distinct sea anemone toxins on crustacean and insect sodium channels. Toxicon 30, 1365-1381; Bruhn, T., Schaller, C., Schulze, C., Sanchez-Rodriquez, J., Dannmeier, C., Ravens, U., Heubach, J.F., Eckhardt, K., Schmidtmayer, J., Schmidt, H., Aneiros, A., Wachter, E., Beress, L., 2001. Isolation and characterization of 5 neurotoxic and cardiotoxic polypeptides from the sea anemone Anthopleura elegantissima. Toxicon, 39, 693-702]. Comprehensive analysis of the purified active fractions suggests that CgNa may represent the main peptide toxin of this sea anemone species. (c) 2006 Elsevier Ltd. All rights reserved.