Hepatocellular Na+/H+ exchange is activated early, transiently and at a posttranscriptional level during rat liver regeneration

Pathophysiology of hepatic Na+/H+ exchange (Review)

Na+/H+ exchangers (NHEs) are a family of membrane proteins that contribute to exchanging one intracellular proton for one extracellular sodium. The family of NHEs consists of nine known members, NHE1-9. Each isoform represents a different gene product that has unique tissue expression, membrane localization, physiological effects, pathological regulation and sensitivity to drug inhibitors. NHE1 was the first to be discovered and is often referred to as the 'housekeeping' isoform of the NHE family. NHEs are not only involved in a variety of physiological processes, including the control of transepithelial Na+ absorption, intracellular pH, cell volume, cell proliferation, migration and apoptosis, but also modulate complex pathological events. Currently, the vast majority of review articles have focused on the role of members of the NHE family in inflammatory bowel disease, intestinal infectious diarrhea and digestive system tumorigenesis, but only a few reviews have discussed the role of NHEs in liver disease. Therefore, the present review described the basic biology of NHEs and highlighted their physiological and pathological effects in the liver.

Metabolic control patterns in acute phase and regenerating human liver determined in vivo by 31-phosphorus magnetic resonance spectroscopy

OBJECTIVE

To elucidate the metabolic changes occurring within hepatocytes during acute phase reaction and liver regeneration.

SUMMARY BACKGROUND DATA

The metabolic events occurring within the liver during the hepatic stress response are poorly understood. The authors used in vivo 31-phosphorus magnetic resonance spectroscopy to study hepatic metabolism after surgical trauma with and without loss of liver cell mass.

METHODS

Three groups were studied: five patients undergoing partial hepatectomy; five patients in whom laparotomy and colonic resection was performed; and five patients treated by thyroidectomy. Hepatic metabolism was evaluated by 31-phosphorus magnetic resonance spectroscopy before surgery and serially thereafter on postoperative days 2, 4, 6, 14, and 28. Estimation of liver volume by magnetic resonance imaging and blood sampling for biochemistry were performed at the same time points.

RESULTS

The authors found that alterations in hepatocyte phospholipid metabolism occurred after surgery that were correlated with changes in circulating acute phase proteins. Liver regeneration after hepatectomy was also associated with a derangement in energy metabolism, measured by a decrease in the ratio of ATP to its hydrolysis product inorganic phosphate. The depleted energy status was mirrored in biochemical indices of liver function, and restitution paralleled the course of restoration of hepatic cell mass.

CONCLUSIONS

These findings indicate that changes in liver metabolism after surgery reflect the magnitude of tissue injury and the quantity of functioning liver cells. Acute phase responses dominate the initial recovery period at the expense of less important endergonic functions. When liver parenchyma is lost, the acute phase reaction is maintained and further supported by a rapid replenishment of hepatocytes, which can even be considered a continuation of acute phase physiology. Modulation of liver function within the framework of overall hepatic energy economy is one mechanism for matching energy supply with increased demands during these processes.

Solvent isotope effect on bile formation in the rat

2H2O affects many membrane transport processes by solvent and kinetic isotope effects. Since bile formation is a process of osmotic filtration where such effects could be important, we investigated the effects of 2H2O on bile formation in the in situ perfused rat liver. Dose finding experiments showed that at high concentrations, 2H2O increased vascular resistance and induced cholestasis; at 60% 2H2O however, a clear dissociation between the vascular and biliary effects was observed. Therefore, further experiments were carried out at this concentration. The main finding was a reduction in bile salt-independent bile flow from 0.99 +/- 0.04 to 0.66 +/- 0.04 microliters.min-1.g-1 (P < 0.001). This was associated with a 40% reduction in biliary bicarbonate concentration (P < 0.001). Choleretic response to neither taurocholate nor ursodeoxycholate was altered by 2H2O; in particular, there was a similar stimulation of bicarbonate secretion by ursodeoxycholate in the presence of 60% 2H2O. To further elucidate this phenomenon, the effect of 2H2O on three proteins potentially involved in biliary bicarbonate secretion was studied in vitro. 2H2O slightly inhibited cytosolic carboanhydrase and leukocyte Na+/H(+)-exchange, these effects reached statistical significance at 100% 2H2O only, however. In contrast, Cl-/HCO(3-)-exchange in canalicular membrane vesicles was already inhibited by 50% (P < 0.001) at 60% 2H2O. Finally, there was a slight reduction in biliary glutathione secretion while that of the disulphide was not affected. Our results are compatible with an inhibition of canalicular Cl-/HCO(3-)-exchange by 2H2O. Whether this is due to altered hydration of the exchanger and/or of the transported bicarbonate remains to be determined.