Prostaglandin F2a Inhibits the Ammoniagenic Response to Acute Acidosis in LLC-PKI Cells1

A kidney epithelial cell line, LLC-PK1, which does not synthesize prostaglandins, provides an ideal in vitro model system to investigate the effect of prostaglandins in the regulation of renal ammoniagenesis. Previous studies from our laboratory have demonstrated significant increases in glutamine-dependent ammonia and alanine production by rocked cultures of LLC-PK1 cells subjected to either acute metabolic or respiratory acidosis. In the study presented here, experiments were conducted to investigate the role of prostaglandin F2a (PGF2a) and prostaglandin E2 (PGE2) in the response of ammonia metabolism to acute metabolic acidosis by LLC-PK1 cells. A low dose of PGF2a (0.1 ng/mL) dramatically inhibited the stimulatory effect of a low pH (pH 6.8) on ammonia production. In contrast, the inhibition of cytosolically generated alanine was less dramatic and averaged only 20% of the effect on ammonia production. Furthermore, PGF2a increased cellular a-ketoglutarate concentration, suggesting an increase in intramitochondrial pH. Thus, the cellular mechanism of PGF2 action appears to involve either interference with the cytosolic pH signal or its translation to the intramitochondrial compartment. The inhibitory response of PGF2,. on pH-stimulated ammoniagenesis was progressively lost at higher concentrations. Both lowdose (0.1 ng/mL) and high-dose (10 ng/mL) PGF2a had no significant effect on the basal rates of ammonia and alanine production at pH 7.4. PGE2, on the other hand, did not exhibit any significant response I The data presented in this report have been published in the form of an abstract in the Annual Meeting ofthe American Federation otCiinicoi Research, 1988;35:597A. 2 Correspondence to Dr. A. 5ahai, Department of Medicine, Room 7900, LAC/ USC Medical Center, 1200 N. State Street, Los Angeles, CA 90033. I046-667310 106-0882$02.00l0 Journal of the American Society of Nephrology Copyright C 1990 by the American Society of Nephrology on ammonia or alanine production at either pH 6.8 or 7.4 when given in a wide range of doses. These studies demonstrate that PGF2a, and not PGE2, is the cyclooxygenase product that inhibits the acute low pH stimulation of ammoniagenesis. The cellular mechanism appears to involve a change in intracellular pH. Furthermore, the differential dose-responsive effect of PGF2r on the low pH stimulation of ammoniagenesis raises the possibility either that LLCPK1 cells have two classes of PGF20 receptors, which exhibit disparate effects on the ammoniagenic response to acidosis and/or that low and high doses of PGF2a may induce disparate responses on intracellular mediators by some other mechanism.