[Effect of caffeine on calcium transport in mitochondria from rat liver (author's transl)]

The influence of caffeine on the calcium transport through membrane has been studied in recently isolated mitochondria from rat liver. Incubated respiring mitochondria in 1.5 X 10(-4) M Ca2+ solutions, show a 2-3 minutes delay in the beginning of calcium uptake in presence of caffeine, independently of the drug concentration (5.1 X 10(-5) M or 2.5 X 10(-4) M). At a higher concentration (5.1 X 10(-4) M) Ca2+ influx is completely inhibited at least during 5 minutes. Ruthenium red stops the influx reaction acting in the same way as in absence of caffeine. A rapid Ca2+ efflux induced by caffeine is observed in mitochondria with a high calcium content (60-90 nmole/mg protein) that stops when the initial level is reached (15 nmol/mg protein). An accummulation of Ca2+ ions in the intracellular media is to be expected due to the presence of caffeine, as it has an inhibition effect on the calcium uptake mechanism of mitochondria and induces the exit of Ca2+ ions even in a high external calcium concentration (10(-4) M).