Uptake of safranine by cardiac mitochondria. Competition with calcium ions and dependence on anions.

Some characteristics of the energized uptake of safranine by rat heart mitochondria were studied. When monitored by changes in differential absorbance (between 524 and 554 nm) of a whole suspension in safranine-containing medium, the changes seen are not linearly related to the quantity of the safranine moving. It happens coincidentally that the changes observed are nearly linearly related to the logarithm of the ratio between the accumulated safranine and its residual concentration in the medium; this explains why the changes of absorbance have been found by other authors to be linearly related to the logarithms of the ratio of internal/external concentrations of such other cations as are permeable. The uptake process appears to compete for energy with Ca2+ uptake and vice versa. Energized safranine uptake has an anion requirement, which is seen when movement of endogenous Pi has been inhibited; the small residual safranine uptake obtained when energy is provided in the presence of mersalyl may be attributable to internal Pi. However, a limited anion-independent energized uptake of safranine, in exchange for internal K+, may be elicited in the presence of nigericin. Adding ATP to the energized system in the presence of an inhibitor of Pi movement elicits an additional uptake of safranine that is oligomycin-sensitive and that probably arises on account of generation of internal Pi by hydrolysis of the entering ATP.