Tetrodotoxin-resistant and tetrodotoxin-sensitive sodium channels in rat dorsal root ganglion neurons differed significantly in 50% inactivation voltage (-40 vs -70 mV) and activation kinetics (-15 vs -26 mV).
TTX-S and TTX-R sodium channels in rat DRG neurons exhibit distinct biophysical properties, developmental expression profiles, and pharmacological sensitivities to neurotoxins, local anesthetics, and divalent cations.
TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) sodium channel currents were analyzed in acutely dissociated dorsal root ganglion (DRG) neurons isolated from 3-12-d-old and adult rats. Currents were recorded using the whole-cell patch-clamp technique. TTX-R current was more likely to be present in younger animals (3-7 d), whereas TTX-S current was more common in older animals (7-10 d), although TTX-R current was recorded from adult rat DRG neurons. The TTX-R and TTX-S currents differed in their steady-state inactivation, with 50% inactivation voltage at -40 +/- 5 mV (n = 10) for TTX-R currents and -70 +/- 4 mV (n = 10) for TTX-S currents. These current types also differed in their activation kinetics, with 50% activation values of -15 +/- 5 mV (n = 5) for TTX-R currents and -26 +/- 6 mV (n = 5) for TTX-S currents. The interactions of TTX-R and TTX-S channels with various pharmacological agents and divalent cations were studied. The Kd values for TTX-S and TTX-R currents were estimated to be 0.3 nM and 100 microM for TTX, 0.5 nM and 10 microM for saxitoxin, and 50 microM and 200 microM for lidocaine, respectively. TTX-S channels did not exhibit a marked use-dependent block by lidocaine, whereas lidocaine significantly decreased TTX-R current in a use-dependent manner at frequencies ranging from 1 to 33.3 Hz. Several external divalent cations exerted different effects on these current types.(ABSTRACT TRUNCATED AT 250 WORDS)
Roy et al. (Mon,) conducted a other in None (healthy rat neurons). Tetrodotoxin, saxitoxin, lidocaine, and divalent cations vs. Control (toxin/drug-free solution) was evaluated on Sodium channel current activation/inactivation kinetics and pharmacological block (Kd values). Tetrodotoxin-resistant and tetrodotoxin-sensitive sodium channels in rat dorsal root ganglion neurons differed significantly in 50% inactivation voltage (-40 vs -70 mV) and activation kinetics (-15 vs -26 mV).