Ruthenium red inhibits the mitochondrial Ca2+ uptake in intact bovine spermatozoa and increases the cytosolic Ca2+ concentration.

The uptake and cycling of Ca2+ by ejaculated bovine spermatozoa are almost completely abolished by ruthenium red, antimycin A or FCCP. The inhibitory effect of ruthenium red is also observed after washing of the dye-pretreated cells followed by addition of digitonin or filipin. In contrast, the inhibition is overcome by A23187 treatment. It is concluded that ruthenium red penetrates into intact spermatozoa, inhibits the mitochondrial Ca2+ uptake 'in situ', and causes the observed increase of the cytosolic free Ca2+ concentration.