Ruthenium red as an effective blocker of calcium and sodium currents in guinea‐pig isolated ventricular heart cells

The effect of ruthenium red on calcium and sodium currents was studied in guinea-pig isolated ventricular heart cells with the whole cell patch-clamp technique. 2. Ruthenium red very efficiently blocked the L-type calcium current in a dose-dependent manner. A significant block was observed for concentrations as low as 0.3 microM. Analysis of the dose-response curve with the logistic equation indicated an EC50 of 0.8 microM, a maximum inhibition of 85% reached at 5 microM, and a coefficient of 2.37. 3. There was no shift in the voltage-dependence of the Ca current activation, nor in that of its steady-state inactivation determined with a 1 s prepulse. However, removal of Ca current inactivation at positive voltage was considerably reduced in the presence of concentrations of ruthenium red above 1 microM. A slowing of the time-course of inactivation of the Ca current was also observed. 4. At 10 microM, a concentration generally used to block the sarcoplasmic Ca release channels or the mitochondrial Ca uptake, ruthenium red blocked 26.7+/-4.3% (n=8) of the sodium current, and slowed its inactivation time-course. No effect was observed on the voltage-dependence of the current activation or inactivation. The peak sodium current was also decreased at a 10 times lower concentration by 7.6+/-2.7% (n=3). 5. Thus, at concentrations used to assess intracellular Ca movements, ruthenium red induced in heart cells a significant block of both Ca and Na channels.