Altered transmembrane ionic flux in hepatocytes isolated from cirrhotic rats

Hepatitis B Virus Infection of Normal Hepatic Stem/Progenitor Cells

BACKGROUND/AIMS

Whether the hepatitis B virus (HBV) infects normal hepatic stem/progenitor cells (NSCs) and if so, whether such infections play a role in the pathogenesis of HBV-induced chronic liver disease (CLD) and/or hepatocellular carcinoma (HCC) remains to be determined. The objectives of this study were to determine whether HBV infects NSCs and whether such infections alter NSC activity in a manner likely to contribute to the development of CLD and/or HCC.

METHODS

Liver biopsies from five hepatitis B surface antigen (HBsAg) positive patients were co-stained for HBcAg and HBx and the stem cell markers EpCAM, Oct-4 and Nanog. In addition, primary NSCs derived from healthy human livers were exposed to HBV contaminated serum in vitro. Supernatant and/or cellular HBsAg, HBcAg and HBV-DNA expression were documented over the subsequent 30 days of culture. Pro- and anti-inflammatory cytokine expression, membrane potential differences (PDs), proliferative and telomerase activities of HBV-infected NSCs were also documented.

RESULTS

Markers of HBV infection were present within the NSC population of all five biopsy specimens. In vitro, HBV markers appeared within three days of exposure, peaked in expression after 10-15 days and remained positive thereafter for the duration of cell viability. There were no consistent changes in HBV-infected NSC pro- or anti-inflammatory cytokine expression, membrane PDs, proliferative or telomerase activities.

CONCLUSIONS

Although the results of this study need to be confirmed, they suggest that HBV infects human NSCs but in the short term, do not alter those NSC features or activities associated with CLD and/or HCC.

Decreased hepatocyte membrane potential differences and GABAA-beta3 expression in human hepatocellular carcinoma

To determine whether hepatocyte membrane potential differences (PDs) are depolarized in human HCC and whether depolarization is associated with changes in GABAA receptor expression, hepatocyte PDs and gamma-aminobutyric acid (GABA)A receptor messenger RNA (mRNA) and protein expression were documented in HCC tissues via microelectrode impalement, real-time reverse-transcriptase polymerase chain reaction, and Western blot analysis, respectively. HCC tissues were significantly depolarized (-19.8+/-1.3 versus -25.9+/-3.2 mV, respectively [P<0.05]), and GABAA-beta3 expression was down-regulated (GABAA-beta3 mRNA and protein expression in HCC; 5,693+/-1,385 and 0.29+/-0.11 versus 11,046+/-4,979 copies/100 mg RNA and 0.62+/-0.16 optical density in adjacent tumor tissues, respectively [P=0.002 and P<0.0001, respectively]) when compared with adjacent nontumor tissues. To determine the physiological relevance of the down-regulation, human malignant hepatocytes deficient in GABAA-beta3 receptor expression (Huh-7 cells) were transfected with GABAA-beta3 complementary DNA (cDNA) or vector alone and injected into nu/nu nude mice (n=16-17 group). Tumors developed after a mean (+/-SD) of 51+/-6 days (range: 41-60 days) in 7/16 (44%) mice injected with vector-transfected cells and 70+/-12 days (range: 59-86 days) in 4/17 (24%) mice injected with GABAA-beta3 cDNA-transfected cells (P<0.005).

CONCLUSION

The results of this study indicate that (1) human HCC tissues are depolarized compared with adjacent nontumor tissues, (2) hepatic GABAA-beta3 receptor expression is down-regulated in human HCC, and (3) restoration of GABAA-beta3 receptor expression results in attenuated in vivo tumor growth in nude mice.

Assessing the cellular transmembrane electrical potential difference on the hepatic uptake of palmitate

Understanding the driving forces for the hepatic uptake of endogenous and exogenous substrates in isolated cells and organs is fundamental to describing the underlying hepatic physiology/pharmacology. In this study we investigated whether uptake of plasma protein-bound [3H]-palmitate across the hepatocyte wall is governed by the transmembrane electrical potential difference (PD). Uptake was studied in isolated hepatocytes and isolated perfused rat livers (IPL). Protein-binding and vasoactive properties of the different perfusates were determined using in vitro heptane/buffer partitioning studies and the multiple indicator dilution (MID) technique in the IPL, respectively. Altering hepatocyte PD by perfusate ion substitution resulted in either a substantial depolarization (-14 +/- 1 mV, n = 12, mean +/- S.E., substituting choline for Na+) or hyperpolarization (-46 +/- 3 mV, n = 12, mean +/- S.E., substituting nitrate for Cl-). Perfusate ion substitution also affected the equilibrium binding constant for the palmitate-albumin complex. IPL studies suggested that, other than with gluconate buffer, hepatic [3H]-palmitate extraction was not affected by the buffer used, implying PD was not a determinant of extraction. [3H]-Palmitate extraction was much lower (p < 0.05) when gluconate was substituted for Cl- ion. This work contrasts with that for the extraction of [3H]-alanine where hepatic extraction fraction was significantly reduced during depolarization. Changing the albumin concentration did not affect hepatocyte PD, and [3H]-palmitate clearance into isolated hepatocytes was not affected by the buffers used. MID studies with vascular and extravascular references revealed that, with the gluconate substituted buffer, the extravascular volume possibly increased the diffusional path length thus explaining reduced [3H]-palmitate extraction fraction in the IPL.

Inhibitory effects of berberine on ion channels of rat hepatocytes

AIM: To examine the effects of berberine, an isoquinoline alkaloid with a long history used as a tonic remedy for liver and heart, on ion channels of isolated rat hepatocytes.

METHODS: Tight-seal whole-cell patch-clamp techniques were performed to investigate the effects of berberine on the delayed outward potassium currents (I_K), inward rectifier potassium currents (I_K1) and Ca²⁺ release-activated Ca²⁺ currents (I_CRAC) in enzymatically isolated rat hepatocytes.

RESULTS: Berberine 1-300 μmol/L reduced I_K in a concentration-dependent manner with EC₅₀ of 38.86 ± 5.37 μmol/L and n_H of 0.82 ± 0.05 (n = 8). When the bath solution was changed to tetraethylammonium (TEA) 8 mmol/L, I_K was inhibited. Berberine 30 μmol/L reduced I_K at all examined membrane potentials, especially at potentials positive to +60 mV (n = 8, P < 0.05 or P < 0.01 vs control). Berberine had mild inhibitory effects on I_K1 in rat hepatocytes. Berberine 1-300 μmol/L also inhibited I_CRAC in a concentration-dependent fashion. The fitting parameters were EC₅₀ = 47.20 ± 10.86 μmol/L, n_H = 0.71 ± 0.09 (n = 8). The peak value of I_CRAC in the I-V relationship was decreased by berberine 30 μmol/L at potential negative to -80 mV (n = 8, P < 0.05 vs control). But the reverse potential of I_CRAC occurred at voltage 0 mV in all cells.

CONCLUSION: Berberine has inhibitory effects on potassium and calcium currents in isolated rat hepatocytes, which may be involved in hepatoprotection.

Electrophysiological effects of anthopleurin-Q on rat hepatocytes

AIM: To study the effects of AP-Q on CCl₄-induced acute liver injury, delayed outward potassium current (I_K), inward rectifier potassium current (I_K1) and calcium release-activated calcium current (I_CRAC) in isolated rat hepatocytes.

METHODS: A single dose of CCl₄ (10 μg/mL, ip) was injected to induce acute liver injury in rats. Serum aminotransferase activities were determined. Whole cell patch-clamp techniques were used to investigate the effects of AP-Q on delayed outward potassium current (I_K), inward rectifier potassium current (I_K1) and calcium release-activated calcium current (I_CRAC).

RESULTS: AP-Q (3.5 and 7 μg/kg) pretreatment significantly reduced ALT and AST activities. AP-Q 0.1-100 nM produced a concentration-dependent increase of I_K with EC₅₀ value of 5.55±1.8 nM (n=6). AP-Q 30 nM shifted the I-V curve of I_K leftward and upward. CCl₄ 4 mM decreased I_K current 28.6±6.5% at 140 mV. After exposure to CCl₄ for 5 min, AP-Q 30 nM attenuated the decrease of I_K induced by CCl₄ close to normal amplitude. AP-Q 0.01-100 nM had no significant effect on either inward or outward components of I_K1 at any membrane potential examined. AP-Q 0.1-100 nM had no significant influence on the peak amplitude of I_CRAC, either, and did not affect the shape of its current voltage curve.

CONCLUSION: AP-Q has a protective effect on CCl₄-induced liver injury, probably through selectively increased I_K in hepatocytes.

Increasing cell membrane potential and GABAergic activity inhibits malignant hepatocyte growth

Increasing hepatocyte membrane potentials by augmenting GABAergic activity inhibits nonmalignant hepatocyte proliferative activity. The objectives of this study were to document 1) potential differences (PDs) of four malignant hepatocyte cell lines, 2) GABAA receptor mRNA expression in the same cell lines, and 3) effects of restoring malignant hepatocyte PDs to levels approximating those of resting, nonmalignant hepatocytes. Hepatocyte PDs were documented in nonmalignant and malignant (Chang, HepG2, HuH-7, and PLC/PRF/5) hepatocytes with a fluorescent voltage-sensitive dye and GABAA receptor expression by RT-PCR and Western blot analyses. Compared with nonmalignant human hepatocytes, all four malignant cell lines were significantly depolarized (P < 0.0001, respectively). Only PLC/PRF/5 cells had detectable GABAA-beta3 receptor mRNA expression and all cell lines were negative for GABAA-beta3 receptor protein by Western blot analysis. Stable transfection of Chang cells with GABAA-beta3 receptor cDNA resulted in significant increases in PD and decreases in proliferative activity as manifest by decreased [3H]thymidine and bromodeoxyurieine incorporation rates, 4-[3-(4-lodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate activity, a lower mitotic index, prolongation of cell-doubling times, and attenuated growth patterns compared with cells transfected with vector alone. Colony formation in soft agar and the number of abnormal mitoses were also significantly decreased in GABAA-beta3 receptor transfected cells. The results of this study indicate 1) relative to healthy hepatocytes, malignant hepatocytes are significantly depolarized, 2) GABAA-beta3 receptor expression is absent in malignant hepatocyte cell lines, and 3) increasing the PD of malignant hepatocytes is associated with less proliferative activity and a loss of malignant features.