Effect of potassium loading on choline pathways in renal cells.

The effect of potassium loading on 14C-choline incorporation into phospholipids, via choline kinase, was measured in young rats after 10 days on a high potassium (1.34 mEq/g) diet, when urinary potassium excretion rose sixfold. Renal choline kinase activity fell by 20%, from 47.3 +/- SEM 2.2 to 37.8 +/- 1.4 pmol 14C-choline incorporated into phosphorylcholine/min/mg protein in the potassium-loaded rats (p less than 0.005). This inhibition was overcome during 48 h of renal compensatory growth following uninephrectomy. There was a 25% increase in the activity of the enzyme, which was associated with a 24% increase in renal weight in potassium-loaded rats following uninephrectomy. Uninephrectomized rats on a normal diet also showed a 20% increase in both renal choline kinase activity and renal weight compared to sham-operated rats. The effect of potassium loading on 14C-choline incorporation into phospholipids was also studied on renal-derived cells having some of the characteristics of either porcine proximal or canine distal tubule cells. Incubation of either cell type in media with 40 mM potassium for 30 min resulted in a 20-30% decrease in the incorporation of 14C-choline into phospholipids (p less than 0.05). Thus, renal utilization of choline for the incorporation of membrane phospholipids for growth can be partially inhibited by chronic potassium loading in young rats and in cells incubated in vitro with high potassium concentrations. The inhibitory effect of potassium loading on renal phospholipid incorporation can be overcome by the stimulating effect of renal compensatory growth on phospholipid incorporation, resulting in increased growth in the young rat kidney.