Intracellular pH during "chemical hypoxia" in cultured rat hepatocytes. Protection by intracellular acidosis against the onset of cell death.

Abstract

The relationships between extracellular pH (pH.), intracellular pH (pH,), and loss of cell viability were evaluated in cultured rat hepatocytes after ATP depletion by metabolic inhibition with KCN and iodoacetate (chemical hypoxia). pH, was measured in single cells by ratio imaging of 2',7'-biscarboxyethyl-5,6-carboxyfluorescein (BCECF) fluorescence using multiparameter digitized video microscopy. During chemical hypoxia at pH. of 7.4, pH, decreased from 7.36 to 633 within 10 min. pH1 remained at 6.1-6.5 for 30-40 min (plateau phase). Thereafter, pHi began to rise and cell death ensued within minutes, as evidenced by nuclear staining with propidium iodide and coincident leakage of BCECF from the cytoplasm. An acidic pH. produced a slightly greater drop in pH1, prolonged the plateau phase of intracellular acidosis, and delayed the onset of cell death. Inhibition of Na+/H' exchange also prolonged the plateau phase and delayed cell death. In contrast, monensin or substitution of gluconate for Cl-in buffer containing HCO3 abolished the pH gradient across the plasma membrane and shortened cell survival. The results indicate that intracellular acidosis after ATP depletion delays the onset of cell death, whereas reduction of the degree of acidosis accelerates cell killing. We conclude that intracellular acidosis protects against hepatocellular death from ATP depletion, a phenomenon that may represent a protective adaptation against hypoxic and ischemic stress.

Molecular mechanisms of SR 4233-induced hepatocyte toxicity under aerobic versus hypoxic conditions

“…As fructose markedly induces glycolysis and acidosis in hypoxic hepatocytes (Seglen, 1974) or perfused liver (Iles et al, 1980) and as an acidotic pH protects against hypoxic hepatocyte injury (Gores et al, 1989), the protective effect of acidosis against SR 4233 cytotoxicity was investigated. As shown in Table IV monensin, an agent which catalyses the exchange of Na+ for H+ and equalises intracellular pH to that of extracellular pH (Gores et al, 1989), prevented fructose protection. Furthermore extracellular acidosis (pH 6.5) prevented SR 4233 cytotoxicity towards hypoxic hepatocytes without affecting SR 4233 metabolism (results not shown).…”

“…Other investigators have shown that fructose markedly increased the anaerobic production of lactic acid particularly in hypoxic hepatocytes (Seglen, 1974), the classical Pasteur effect, and that significant acidosis developed (Iles et al, 1980). Furthermore acidosis protects against hypoxic injury in hepatocytes (Gores et al, 1989). Because of this the effect of monensin, an agent which catalyses the exchange of Na+ for H+ and has been shown to equalise intracellular pH to that of extracellular pH (Gores et al, 1989) on the fructose protection was investigated.…”

“…Furthermore acidosis protects against hypoxic injury in hepatocytes (Gores et al, 1989). Because of this the effect of monensin, an agent which catalyses the exchange of Na+ for H+ and has been shown to equalise intracellular pH to that of extracellular pH (Gores et al, 1989) on the fructose protection was investigated. It was found that monesin prevented the antidotal effect of fructose.…”

Mitochondrial translocation of α-synuclein is promoted by intracellular acidification

“…One common cellular response to a number of oxidative and metabolic challenges is a reduction of intracellular pH (pHi) [36,39,40]; this is likely an early and essential event during apoptosis and/or necrosis [41]. Mechanisms proposed for cytosolic acidification include: dysregulation of ion transport [42]; proton leakage from acidic organelles [43]; and hydrolysis of high energy nucleotides [44].…”

Cellular acidification occurs during anoxia in cultured, but not in freshly isolated, rabbit proximal tubular cells

“…During 1 h of anoxia, cell viability of freshly isolated PT cells de creased significantly to 54% ± 2% (P < 0.05), while no loss in viability was observed in cultured PT cells. Clamping the pH; during anoxia at 6.7 and 6.1 signifi-shown that acidification of hypoxic tissue, resulting from glycolytic lactate production, ATP hydrolysis and C 0 2 accumulation, can enhance the resistance to the damaging effects of O, deprivation in the kidney [7,24,[26][27][28][29], cardiomyocytes [3,16], and hepatocytes [10,11,13,18]. However, the mechanism behind the protec tion offered by lowering the pH is unknown.…”