The effects of chlorotetracycline on calcium movements in isolated rat liver mitochondria

Chlorotetracycline was used as a fluorescent chelate probe for visualizing calcium movements in rat liver mitochondria. It was demonstrated that under specified conditions, chlorotetracycline-associated fluorescence may be employed as a monitor of calcium uptake by mitochondrial membranes, e.g., at low calcium and Chlorotetracycline concentrations and in the absence of exogenous phosphate or acetate. However, at elevated calcium concentrations, e.g., >0.05 mm, a transient fluorescence response was observed upon addition of calcium to energized mitochondria. This transient or cyclic behavior of the chlorotetracycline-associated fluorescence was minimized by increasing the chlorotetracycline concentration, the mitochondrial protein concentration, or by including magnesium in the incubation. Also, it was demonstrated that chlorotetracycline addition to mitochondria which had been loaded previously with ⁴⁵Ca resulted in a rapid efflux of the accumulated ⁴⁵Ca. Because of the various effects of chlorotetracycline on the ability of the mitochondria to accumulate and to retain calcium, caution must be exercised in the interpretation of experimental results when this fluorescent chelate probe is utilized to monitor the association of divalent metal cations with biological membranes.