EFFECT OF SODIUM-BICARBONATE ON INTRACELLULAR PH UNDER DIFFERENT BUFFERING CONDITIONS

Previous in vitro studies have reported a paradoxical exacerbation of intracellular acidosis following bicarbonate therapy due to the genera ted CO2 entering the cytoplasm. However, these studies were conducted in nonphysiological Hepes-buffered media. We compared the effect of a sodium bicarbonate load on the intracellular pH (pH(i)) of hepatocytes placed in nonbicarbonate (NBBS) or bicarbonate (BBS) buffering system s. The pH(i) of isolated rat hepatocytes was measured using the fluore scent pH sensitive dye BCECF and a single-cell imaging technique. Cell s were placed in medium buffered with HCO3-/CO2 or Hepes. All media we re adjusted to pH 7 with L-lactic acid or HCl. An acute 45 mM sodium b icarbonate load was added to each medium and the changes in pH(i) were measured every three seconds for 90 seconds. The sodium bicarbonate l oad caused rapid cytoplasmic acidification of cells in NBBS (N = 50, P < 0.001). In contrast, hepatocytes in BBS underwent a marked increase in pH, (N = 50, P < 0.001) without any initial decrease in pH(i). The se differences were highly significant for the buffer (P < 0.01), but not for the acid used. We conclude that sodium bicarbonate exacerbates intracellular acidosis only in a NBBS. Hence, in vitro studies report ing a paradoxical intracellular acidosis following bicarbonate therapy cannot be extrapolated to the in vivo buffering conditions, and shoul d not be used to argue against bicarbonate therapy.