GROWTH-REGULATION OF LLC-PK1 CELLS - LACK OF EFFECT OF NA-LOADING()

To gain more information about the growth regulation of renal epitheli al cells, we examined the growth stimulatory effect of serum and intra cellular sodium in the renal epithelial cell line, LLC-PK1. In subconf luent LLC-PK1 cells serum-starved for 5 days and exposed to [H-3]thymi dine for 24 h, 22.9% of the cells synthesized DNA. Stimulation with 10 % foetal calf serum (FCS) caused an almost three-fold increase in the fraction of labelled nuclei (62.2%). Serum-starved LLC-PK1 cells expos ed to 10% FCS responded with an increased abundance of c-jun transcrip ts. The maximal expression of the c-jun transcripts occurred at 60 min and declined 120 min after serum stimulation. It has been suggested t hat an increase in Na+ influx plays a role in the growth regulation of renal epithelial cells. This prompted us to study the effect of intra cellular Na+ loading on the growth response of LLC-PK1 cells. Serum-st arved LLC-PK1 cells were incubated in a low K+ medium or exposed to Ny statin. Incubation in a low K+ medium or with Nystatin resulted in a m arked increase in intracellular Na after only 5 min. A low K+ medium d id not significantly influence the intracellular pH. No effect was obs erved on DNA synthesis or the abundance of c-jun transcripts in LLC-PK 1 cells. Nor did Na+ loading enhance the growth stimulatory effect of serum. The results suggest that an increase in intracellular sodium do es not directly regulate the growth of renal epithelial cells.