LYMPHOCYTIC INTRACELLULAR PH AND NA+ H+ EXCHANGER ACTIVITY IN HEMODIALYSIS-PATIENTS

We have evaluated intracellular pH (pH(i)) and Na+/H+ exchanger activity in peripheral lymphocytes from 16 patients on regular acetate hemodialysis. All the patients were taking oral NaHCO3 supplementation (30 mmol/day), to maintain predialysis arterial blood acid-base status within normal range (pH 7.36 +/- 0.02, P-HCO3- 23.3 +/- 1.2 mM, pCO(2) 40.9 +/- 1.4 mm Hg). pH(i) was measured, using the fluorescent probe BCECF (2',7'-bis-carboxyethyl-5,6-carboxy-fluorescein), both in nominal absence of bicarbonate (Hepes solution, pH 7.4; n = 10) and in the presence of HCO3-/CO2 buffer system (pH 7.4, [HCO3-] 25 mM, pCO(2) 40 mm Hg; n = 6). Predialysis pH(i) did not differ from controls when measured in the presence of HCO3-/CO2 (7.28 +/- 0.04 vs. 7.29 +/- 0.04, p = NS), but was lower in dialysis patients than in normal subjects (7.11 +/- 0.04 and 7.20 +/- 0.02, respectively; p < 0.05) when measured in Hepes solution. This suggested that bicarbonate-independent pH(i) regulation was abnormal in dialysis patients. To further characterize this abnormality of pH(i) regulation, lymphocytes were exposed to ethylisopropylamiloride, a specific Na+/H+ antiporter inhibitor, in Hepes solution; this maneuver induced a significantly lower decrement in pH(i) (0.04 +/- 0.04 vs. 0.15 +/- 0.03, p < 0.05) in dialysis patients than in controls, indicating reduced Na+/H+ exchanger activity in the patients. The rate of pHi recovery during the first 30 s after induction of various degrees of cell acidification (pH(i) range 6.2-7.0), which in the absence of HCO3-/CO2 is dependent on Na+/H(+)exchanger activity, was also reduced in the patients as compared to controls (p < 0.001). These findings demonstrate depressed Na+/H+ exchanger activity in lymphocytes from patients on chronic maintenance hemodialysis; accounting for the lower pH(i) in Hepes solution. However, this abnormality does not prevent pH(i) to be mainteined in the normal range in the presence of the physiological buffer HCO3-/CO2 and possibly in vivo.