Extracellular potassium modifies the structure of kidney epithelial cells in culture

In animals fed a K-deficient diet, alterations in kidney cell structure and function occur in association with changes in the ionic composition of the extracellular fluid. The hypothesis that the extracellular K concentration mediates these changes in renal tissue was tested in cultures of monkey kidney epithelial cells (BSC-1 line) by reducing the K concentration of the culture medium from the control value of 5.4 to 3.2 mM. Exposure of BSC-1 cells to low-K medium raised the maximal rate of uptake for L-glutamic acid by 39% without a change in apparent Km. To determine whether this alteration in plasma membrane function had a structural correlate, studies of the cell surface were performed using scanning and transmission electron microscopy. Morphometric analysis of scanning electron micrographs revealed that the number of microvilli per cell per unit surface area was 45% greater in cells exposed to low-K medium for 3 min than those exposed to control medium. This observation was confirmed by transmission electron microscopy. The results indicate that an alteration in the extracellular K concentration per se can modify specific structural and functional characteristics of kidney epithelial cells.