Ion transport in the heart atrial tissue of young and adult guinea-pigs and albino rats.

Rubidium shifts between the extracellular fluid and cells were studied in the isolated atria of guinea-pig and albino rat hearts. In the young of both species, rubidium transport from the incubation medium to the cells was much slower than in preparations from adult animals. That implies that the efficiency of membrane mechanisms for the transport of Na+ and K+ ions in the atrial tissue increases during postnatal life. This conclusion is further confirmed by the finding that the intracellular potassium concentration in the atrial tissue of the young of both species is lower, and the intracellular sodium concentration higher, than in adult animals. Conversely, the serum potassium concentration in the young is higher, and the serum sodium concentration lower, than in adult individuals.