Calcium transport in isolated guinea-pig atria during metabolic inhibition

Abstract

Investigations were performed in order to study whether in guinea-pig atrial tissue the transport of Ca 2+ across the cell membrane into the extracellular space occurs by means of an energy-requiring active transport. The turnover of 45Ca and the total calcium content were established after metabolic inactivation. Inhibition of energy metabolism was induced by cooling the isolated atria from 30° to either 15° or 1°. In order to determine whether metabolic inactivation was really achieved by this treatment, cellular potassium and sodium were also determined after cooling. 1. 1. During hypothermia cellular sodium increased, whereas the potassium content was lowered. This effect indicates that metabolic inactivation has really taken place. 2. 2. The total cellular calcium content of control preparations proved to be 345 ± 3 nequiv/100 mg tissue (wet. wt.). Lowering of the temperature to 15° provoked an increase in the calcium concentration to a final level of 462 ± 28 nequiv/100 mg. At 1° this increase was even more pronounced and reached a value of 578 ± 44 nequiv/100 mg tissue after incubation for 150 min. 3. 3. During hypothermia the release of 45Ca was inhibited in comparison with that by control organs: at 30° electrically stimulated atria lost 50% of the initial 45Ca after 5 min; for resting left auricles this value was 8 min. At 15°, 20 min were required for this percentage of release and at 1° even 45 min. 4. 4. During hypothermia (15°) the uptake of 45Ca by the cell was only slightly diminished. 5. 5. The results obtained after hypothermia suggest that the transport of Ca 2+ out of the heart-muscle cell may occur by means of an energy-requiring calcium pump mechanism.