What is the principal cation in intracellular fluid?

The principal cation in intracellular fluid is potassium. This is primarily due to the role potassium plays in maintaining the resting membrane potential of cells and its involvement in various cellular functions. Inside cells, potassium ions are crucial for activities such as protein synthesis, enzyme function, and maintaining fluid balance. The intracellular concentration of potassium is significantly higher than that of sodium, which is predominantly found in extracellular fluid. The high concentration gradient of potassium is vital for cellular processes, including nerve impulse conduction and muscle contraction, by contributing to the electrical charge difference across cell membranes. This characteristic makes potassium the dominant cation in intracellular fluid.