RESUMO
The effects of lubeluzole on sodium currents were examined in guinea-pig isolated cardiac myocytes by use of the whole-cell patch clamp technique. Lubeluzole (0.01-100 microM) reduced peak Na+ current (INa) obtained at a holding potential of -80 mV with an IC50 value of 9.5 (3.5-21.9) microM and a Hill coefficient of 1.1. These effects were rapid and reversible. Lubeluzole (10 microM) produced a shift in the inactivation curve to hyperpolarized potentials (by -9.7 mV, P < 0.05), but produced no change in the voltage-dependence of activation. Lubeluzole (10 microM) produced significant tonic block of INa obtained at a holding potential of -120 mV (2.7 +/- 1.4% and 27.5 +/- 5.8% for control and lubeluzole, respectively; n = 6; P < 0.05). Use-dependent block of INa was also observed. Recovery from block was delayed by lubeluzole (10 microM; tau1=4.4 +/- 6.2, tau2=22.7 +/- 1.5 milliseconds for control and tau1=311 +/- 144, tau2 = 672 +/- 23 milliseconds for lubeluzole; n = 6; P < 0.001) confirming use-dependency of block. The results indicate that lubeluzole produces both tonic and use-dependent block of cardiac sodium channels at concentrations similar to those that block neuronal sodium channels, due mainly to interaction of the drug with channels in the inactivated state.
