NH4+ metabolism and the intracellular pH in isolated perfused rat liver

Abstract

The effects of NH4+ on the intracellular pH (pHi) and on the ATP content in isolated perfused rat liver were studied by 31P n.m.r. spectroscopy. In the initial phase of perfusion an average pHi of 7.29 +/- 0.04 was estimated. The presence of low (0.5 mmol/l) and high (10 mmol/l) doses of NH4Cl induced significant intracellular acidification by -0.06 +/- 0.03 and -0.11 +/- 0.03 pH unit respectively. This effect was in contrast with the transient intracellular alkalinization observed in preliminary studies on isolated hepatocytes, which was caused by a passive entry of NH3 by non-ionic diffusion and subsequent conversion into NH4+. During application of 0.5 mmol/l NH4Cl the liver released 0.54 +/- 0.06 mumol of urea/min per g into the perfusate. When the intracellular availability of HCO3- was decreased by acetazolamide (0.5 mmol/l) or by removal of HCO3- from the perfusion medium, the decrease in pHi by NH4Cl application was significantly lower than under control conditions. Furthermore, synthesis of urea was significantly inhibited by the decrease in intracellular HCO3-. Under these conditions, 10 mmol/l NH4Cl caused the transient alkalinization that was expected because of the passive uptake of uncharged NH3. Therefore, it is concluded that the intracellular acidification induced by NH4Cl is caused by the continuous utilization of intracellular HCO3- via the synthesis of urea. This metabolic effect on pHi dominates the effects of passive NH3 entry. The rate of urea formation depends on continuous efflux of H+, which is strictly limiting the degree of intracellular acidification within a small range. If the extrusion of H+ by the Na+/H+ exchanger was inhibited by amiloride (0.5 mmol/l) during the NH4Cl application, the decrease in pHi was amplified and the formation of urea was significantly inhibited. The application of NH4Cl at 0.5 or 10 mmol/l decreased the ATP content by 11% or 22% respectively.

Ion regulation in the different life stages of Trypanosoma cruzi

“…This process induced acidification in all three forms, which explains their capacity to regulate their internal pH after severe basification of the cytoplasm. This effect has also been reported by Zange et al (1993) when working with isolates from rat liver incubated in the presence of NH 4 Cl.…”

“…Zange et al (1993) and Henderson et al (1987) reported that in media with HCO ) 3 , the addition of NH + 4 and amiloride or DIDS sharply lowered the pH i in eukaryotic cells. Though the test media used in these experiments were NH 4 + free, the production of NH + 4 by T. cruzi was corroborated by Adroher et al (1988Adroher et al ( , 1998.…”

Hyperammonemia acts synergistically with lipopolysaccharide in inducing changes in cerebral hemodynamics in rats anaesthetised with pentobarbital

“…This observation can be explained by the fact that systemic administration of amiloride also affects the Na + /H + exchanger (IC 50 $84 lM [30]), in the liver. Blocking the Na + /H + exchanger in the liver probably impairs the ammonia detoxification, because the rate of urea synthesis in hepatocytes depends on extrusion of H + [31].…”