Na regulates growth of kidney epithelial cells induced by lowering extracellular K concentration

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Abstract
Accelerated kidney growth and increased tissue Na content have been observed in rats fed a K-deficient diet. These observations suggest that enhanced Na influx could mediate renal growth, a hypothesis that was tested in cultures of kidney epithelial cells of the BSC-1 line. Reduction of the K concentration in the culture medium from 5.4 to 3.2 mM augmented cell growth and induced a transient increase in the cellular content of Na and a decrease in that of K. That low-K-induced growth was Na dependent was shown by decreasing the medium Na concentration from 155 to 150 mM, which abolished the increases in both growth and cell Na content in a concentration-dependent manner. The stimulation of glyceraldehyde-3-phosphate dehydrogenase (G3PD) activity that occurs in cells exposed to low-K medium for 1 h was similarly prevented by decreasing the medium Na concentration. Thus decreased availability of extracellular Na prevented the increase in cell Na content, stimulation of G3PD activity, and accelerated growth induced by low-K medium. The hypothesis was also tested by adding vasopressin to cultures of BSC-1 cells exposed to low-K medium; the hormone prevented the increments in cell Na content, G3PD activity, and growth to the same extent as did decreased availability of extracellular Na. These results are consistent with the interpretation that transient accumulation of Na is a critical determinant of the initiation of kidney epithelial cell growth.