Stimulation of the yeast mitochondrial calcium uniporter by hypotonicity and by ruthenium red

The Ca2+ uptake by mitochondria from the yeast Endomyces magnusii has earlier been found to be driven by the membrane potential and to be stimulated by spermine. It thus functions in a similar fashion as the animal mitochondrial calcium uniporter. Here, it is shown that the uptake is stimulated, i.e., Ca2+ can be accumulated from lower [Ca2+], under hypotonic conditions. Ruthenium Red, an inhibitor of the animal uniporter, under certain conditions, stimulates the yeast uniporter. The mechanism of the stimulation by hypotonicity and Ruthenium Red is discussed.