Proximal Convoluted Tubule EM

This is an EM section of the proximal convoluted tubule. Note the microvilli forming the brush border on the apical surface. The basal striations in these cells are due to the parallel alignment of mitochondria alongside the basolateral regions of the plasma membrane. Why is there a high concentration of mitochondria on the basolateral surface?

Answer: These mitochondria support active ion transport pumps on the basal plasma membrane by providing an abundant amount of ATP. The ion gradient created by these pumps in turn supports ion and water reabsorption on the apical side of the proximal convoluted tubule cells.