Final answer:
The most abundant cation in intracellular fluid is potassium (K+), which is essential for cellular function and is actively maintained by sodium-potassium pumps using energy from ATP.
Step-by-step explanation:
The most abundant cation in intracellular fluid is potassium (K+). This ion is crucial for numerous cellular functions, including establishing the resting membrane potential in neurons and muscle fibers after membrane depolarization and action potentials. Potassium concentration is maintained within cells mainly by the sodium-potassium pumps located in the cell membrane, which actively transport potassium into the cell against its concentration gradient, using ATP as the energy source. Unlike sodium, potassium does not significantly affect osmotic pressure, but it is essential for the overall function of cells.
Intracellular fluid contains a higher concentration of potassium compared to the extracellular fluid (ECF), where sodium (Na+) is the predominant cation. The concentration of potassium inside cells is approximately 30 times higher than outside, which is critical for the electrical neutrality and osmotic balance of the cell. Chloride (Cl-), on the other hand, is the predominant extracellular anion and works in tandem with sodium to maintain the osmotic pressure gradient and hydration between the intracellular and extracellular spaces.