Cells maintain low internal concentrations of sodium (Na+) and high internal concentrations of potassium (K+) primarily due to the function of the sodium-potassium ATPase pump. This pump expels three Na+ ions from the cell while bringing in two K+ ions, using ATP for energy. This process is crucial for various cellular functions, including glucose transport across the intestinal epithelium, where glucose is co-transported with Na+ into the cell. The expulsion of Na+ helps maintain osmotic balance and stabilizes cell volume, preventing swelling and potential bursting. Additionally, the pump contributes to the generation of membrane potential in nerve cells, essential for action potential propagation. The presence of negatively charged organic molecules, such as amino acids and DNA, within cells necessitates the influx of cations like K+ to maintain charge balance and osmotic gradients.
