Vol. 303, Issue 3, 1067-1074, December 2002

The Sea Anemone Toxins BgII and BgIII Prolong the Inactivation Time Course of the Tetrodotoxin-Sensitive Sodium Current in Rat Dorsal Root Ganglion Neurons

Emilio Salceda, Anoland Garateix and Enrique Soto

Instituto de Fisiología, Universidad Autónoma de Puebla, México (Em.S., En.S.); and Instituto de Oceanología, Ministerio de Ciencia, Tecnologia y Medio Ambieute, La Habana, Cuba (A.G.)

We have characterized the effects of BgII and BgIII, two sea anemone peptides with almost identical sequences (they only differ by a single amino acid), on neuronal sodium currents using the whole-cell patch-clamp technique. Neurons of dorsal root ganglia of Wistar rats (P5-9) in primary culture (Leibovitz's L15 medium; 37°C, 95% air/5% CO₂) were used for this study (n = 154). These cells express two sodium current subtypes: tetrodotoxin-sensitive (TTX-S; K_i = 0.3 nM) and tetrodotoxin-resistant (TTX-R; K_i = 100 µM). Neither BgII nor BgIII had significant effects on TTX-R sodium current. Both BgII and BgIII produced a concentration-dependent slowing of the TTX-S sodium current inactivation (IC₅₀ = 4.1 ± 1.2 and 11.9 ± 1.4 µM, respectively), with no significant effects on activation time course or current peak amplitude. For comparison, the concentration-dependent action of Anemonia sulcata toxin II (ATX-II), a well characterized anemone toxin, on the TTX-S current was also studied. ATX-II also produced a slowing of the TTX-S sodium current inactivation, with an IC₅₀ value of 9.6 ± 1.2 µM indicating that BgII was 2.3 times more potent than ATX-II and 2.9 times more potent than BgIII in decreasing the inactivation time constant (_h) of the sodium current in dorsal root ganglion neurons. The action of BgIII was voltage-dependent, with significant effects at voltages below 10 mV. Our results suggest that BgII and BgIII affect voltage-gated sodium channels in a similar fashion to other sea anemone toxins and -scorpion toxins.