INTRACELLULAR ACIDIFICATION MEDIATES THE INHIBITORY EFFECT OF PERITONEAL DIALYSATE ON PERITONEAL-MACROPHAGES

Commercial peritoneal dialysis solution (CDS) is known to have a detri mental effect on the capacity of peritoneal macrophages (PM Phi) to ki ll bacteria and produce acute phase cytokines, This cytotoxic effect i s largely caused by the low pH of CDS. Because the cytoplasmic pH (pHi ) is an important determinant of cellular function, the effect of CDS on the pHi of PM Phi from continuous ambulatory peritoneal dialysis pa tients was studied. The pHi of PM Phi was measured fluorometrically in N-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered sa lt solution (HBSS) or CDS at pH values of 5.3, 6.5, and 7.0, values th at represent the pH existing in dialysate during the first 30 min of d well time. For any given pH of the experimental medium, the pHi was al ways more acidic in CDS than in HBSS. When PM Phi were incubated with a lactate-containing HBSS, a cellular acidification was observed that was similar to that attained by exposure to CDS at the same pH. This s upports the hypothesis that the decrease in pHi was due to the influx of lactic acid from the CDS into the PM Phi. In order to demonstrate a causal association between the CDS-induced cellular acidification and a defect in phagocytosis and cytokine production, these functions wer e studied after pHi clamping by means of K+/nigericin, It was found th at clamping pHi to values below 6.5 led to a markedly reduced tumor ne crosis factor-alpha production and phagocytosis. However, at values of pHi >6.5, these functions were normal. The acid loading of PM Phi wit h CDS was followed by a partial recovery of pHi toward the resting pHi . This recovery reflects the activity of the Na+/H+ exchanger, as evid enced by its sensitivity to amiloride and an H+-ATPase sensitive to N, N-dicyclohexylcarbodiimide. It was concluded that: (1) exposure of PM Phi to CDS causes a profound drop in pHi due to the cellular accumulat ion of lactic acid, (2) The CDS-mediated PM Phi acidosis probably play s a major role in the known inhibitory effect of CDS on phagocytosis a nd cytokine production, (3) The partial recovery of pHi observed after the exposure of the cells to CDS of pH 6.5 and 7.0 was mediated by an Na+/H+ antiporter and a proton ATPase.