| Abstrakt: |
The role of sodium in calcium active transport from the ureter muscle, preliminarily enriched in these ions, was studied in large ouabain concentration (10(-4) mmol/l) for complete inhibition of the Na(+)-K(+)-pump. The determination of intracellular concentrations of sodium and calcium ions (by flame photometry and isotopic analysis, resp.) showed that a fast decrease of intracellular calcium content was accompanied by an increase of intracellular sodium. With high sodium ions concentration in medium (above 100 mmol/l), the velocity of the decrease in intracellular calcium content reached the maximal value, the efflux of additional enriched calcium ions occurring within 10-15 min. The decrease of intracellular calcium content was in sigmoidal dependence on the concentration of sodium ions in the medium. The electrogenic Na(+)-Ca(++)-exchange system seems to play a major role in calcium-enriched muscles for the decrease of intracellular calcium content. |
