BICARBONATE VERSUS LACTATE BUFFER IN PERITONEAL-DIALYSIS SOLUTIONS - THE BENEFICIAL EFFECT ON RBC METABOLISM

Objective: Using the erythrocyte as a model for other kinds of cells n ot directly exposed to peritoneal dialysis (PD) solutions, we investig ated the tolerance of the cell metabolism to lactate and bicarbonate b uffers. Design: We studied, in vivo (in two groups of 5 PD patients ea ch) and in vitro, the Embden-Meyerhof pathway (EMP) because it represe nts a potential target for the unphysiological effects of lactate or b icarbonate buffers. The EMP is the main glucose-utilizing route in the red blood cell (RBC), producing energy and reducing power. Methods: T he enzymatic activities of the key steps in the glycolytic pathway and the energy charge (EC), determined by the levels of phosphorylated ad enine nucleotides, were investigated spectrophotometrically and by hig h performance liquid chromatography (HPLC)in two groups of patients un dergoing lactate (L-group) and bicarbonate (B-group) PD, respectively. The in vitro effects of both bicarbonate and lactate buffers on some EMP enzyme activities and energy production were determined. Cellular pH (pHi) was also investigated. Results: The B-group showed an EC valu e near the control levels, while in the L-group a significantly lower EC Value was observed (West: p < 0.05 vs both B-group and controls). T he key enzymes in the EMP, and in particular hexokinase, were higher i n the L- versus B-group (p < 0.03 for the comparison of the Hk mean va lues). As demonstrated by sodium dodecyl sulfate-polyacrylamide gel el ectrophoresis analysis, the bound form of glyceraldehyde-3-phosphate d ehydrogenase (GS-PD), an inactive form of this EMP enzyme, was signifi cantly higher in the L-group with respect to the B-group (p < 0.004). In the in vitro experiments, high lactate concentrations acutely inhib ited the key enzymatic steps of glycolysis, producing a significant de crease in glucose consumption and adenosine triphosphate production. T hese effects were not observed when bicarbonate was used in the incuba tions. Both in vivo and in vitro lactate, but not bicarbonate, induce a significant drop in pHi (p < 0.05). Decreased levels of pHi like tho se observed in the lactate-incubated RBC were demonstrated to be able to inhibit G-3-PD activity (25+/-2%) here used as an indicator of the actual decrease in pH. Conclusion: This study provides evidence for a damaging action of lactate with respect to bicarbonate buffer on the R BC metabolism. This condition was demonstrated observing a cell energy depletion, which coincides in vitro with an acute EMP impairment; the lactate accumulation together with the consequent lowering of pHi see m to be responsible for this effect, which was not observed when bicar bonate was used instead of lactate.