More on Hypophosphatemia

To the Editor: The otherwise excellent update on the clinical status of hypophosphatemia (August 15 issue)¹ contains an inaccurate statement that should be corrected. Knochel states that “a major regulator of the cytoplasmic calcium concentration is sodium–calcium exchange across the cell membrane.” Although there is no doubt that sodium–calcium exchange is an important system that transfers calcium ions across the cell membrane and contributes to the total calcium content of the cell, there is also evidence that it has little or no effect on cytosolic levels of calcium. Cells contain complicated and not fully defined mechanisms that enable them to…