Use of ruthenium red as an inhibitor of mitochondrial Ca(2+) uptake in single rat cardiomyocytes.

With the current resurgence of interest in the role of mitochondrial [Ca(2+)] in energy production and cellular Ca(2+) signalling, ruthenium red (RR) is being increasingly used as an inhibitor of mitochondrial Ca(2+) uptake. In the present study, the effects of RR on cell and mitochondrial [Ca(2+)], and on cell contractility were determined in isolated rat ventricular myocytes subjected to adrenergic and electrical stimulation. At low concentrations, 0-1 microM, RR inhibited mitochondrial Ca(2+) uptake but this was a secondary effect due to a reduced total intracellular [Ca(2+)], a conclusion supported by the ability of RR to inhibit cell shortening. 5 microM RR completely inhibited cell contraction, whereas higher concentrations, 10-25 microM, induced spontaneous Ca(2+) oscillations and contractile waves. These results indicate that great care must be taken when using RR in intact cells, and in interpreting any effects as resulting from a primary inhibition of mitochondrial Ca(2+) uptake.