Membrane Potential In Hepatocytes Research Articles

PKC-δ-dependent mitochondrial ROS attenuation is involved as 9-OAHSA combats lipoapotosis in rat hepatocytes induced by palmitic acid and in Syrian hamsters induced by high-fat high-cholesterol high-fructose diet

Metabolic-associated fatty liver disease (MAFLD) is a global concern, often undetected until reaching an advanced stage. Palmitic acid (PA) is a type of fatty acid that increases and leads to liver apoptosis in MAFLD. However, there is currently no approved therapy or compound for MAFLD. Recently, branched fatty acid esters of hydroxy fatty acids (FAHFAs), a group of bioactive lipids, have emerged as promising agents to treat associated metabolic diseases. This study utilizes one type of FAHFA, oleic acid ester of 9-hydroxystearic acid (9-OAHSA), to treat PA-induced lipoapoptosis in an in vitro MAFLD model using rat hepatocytes and a high-fat high-cholesterol high-fructose (HFHCHFruc) diet in Syrian hamsters. The results indicate that 9-OAHSA rescues hepatocytes from PA-induced apoptosis and attenuates lipoapoptosis and dyslipidemia in Syrian hamsters. Additionally, 9-OAHSA decreases the generation of mitochondrial reactive oxygen species (mito-ROS) and stabilizes the mitochondrial membrane potential in hepatocytes. The study also demonstrates that the effect of 9-OAHSA on mito-ROS generation is at least partially mediated by PKC-δ signaling. These findings suggest that 9-OAHSA shows promise as a therapy for MAFLD.

Tamarix articulata Induced Prevention of Hepatotoxicity Effects of In Vivo Carbon Tetrachloride by Modulating Pro-Inflammatory Serum and Antioxidant Enzymes to Reverse the Liver Fibrosis.

This study evaluates the hepatoprotective activity of a Tamarix articulata extract against carbon tetrachloride-mediated hepatotoxicity in Wistar rats. Our results demonstrated that the oral administration of Tamarix articulata extract (50 mg/kg b.w.) significantly restored the serum levels of liver enzymes and antioxidant parameters (superoxide dismutase, catalase, glutathione reductase, and thiobarbituric reactive substances). Histopathology analysis revealed that Tamarix articulata extract significantly reduced hepatic fibrosis by inhibiting the necrosis of hepatocytes. Furthermore, serum pro-inflammatory (tumor necrosis factor-alpha, tumor growth factor-beta, and interleukin-6) markers were significantly restored. However, the anti-inflammatory cytokine adiponectin levels increased to normal levels in the group treated with Tamarix articulata extract. Additionally, we observed diminished reactive oxygen species production and the depolarization of mitochondrial membrane potential in hepatocytes extracted from animal livers treated with Tamarix articulata extract. Our findings suggest that Tamarix articulata extract prevents liver fibrosis induced by carbon tetrachloride and decreases the necrotic population of hepatocytes. These events restored the antioxidant enzymatic activity, serum levels of liver enzymes, and pro-inflammatory markers to their normal levels.

Hepatocyte membrane potential regulates serum insulin and insulin sensitivity by altering hepatic GABA release.

SUMMARYHepatic lipid accumulation in obesity correlates with the severity of hyperinsulinemia and systemic insulin resistance. Obesity-induced hepatocellular lipid accumulation results in hepatocyte depolarization. We have established that hepatocyte depolarization depresses hepatic afferent vagal nerve firing, increases GABA release from liver slices, and causes hyperinsulinemia. Preventing hepatic GABA release or eliminating the ability of the liver to communicate to the hepatic vagal nerve ameliorates the hyperinsulinemia and insulin resistance associated with diet-induced obesity. In people with obesity, hepatic expression of GABA transporters is associated with glucose infusion and disposal rates during a hyperinsulinemic euglycemic clamp. Single-nucleotide polymorphisms in hepatic GABA re-uptake transporters are associated with an increased incidence of type 2 diabetes mellitus. Herein, we identify GABA as a neuro-hepatokine that is dysregulated in obesity and whose release can be manipulated to mute or exacerbate the glucoregulatory dysfunction common to obesity.

Calcitriol alleviates ethanol-induced hepatotoxicity via AMPK/mTOR-mediated autophagy

Excessive ethanol consumption causes cellular damage, leading to fetal alcohol syndrome and alcohol liver diseases, which are frequently seen with vitamin D (VD) deficiency. A great deal of progress has been achieved in the mechanisms of ethanol-induced hepatocyte damage. However, there are limited intervention means to reduce or rescue hepatocytes damage caused by ethanol. On the basis of our preliminary limited screen process, calcitriol showed a positive effect on protecting hepatocyte viability. Therefore, the molecular basis is worth elucidating. We found that calcitriol pretreatment markedly improved the cell viability, decreased cell apoptosis and oxidative stress and alleviated the abnormal mitochondrial morphology and membrane potential of hepatocytes induced by ethanol. Notably, autophagy was significantly enhanced by calcitriol, as evident by the increasing number of autophagosomes and autolysosomes, upregulated LC3B-Ⅱ and ATG5 levels, and promotion of p62 degradation. Furthermore, calcitriol pretreatment increased the colocalization of GFP-LC3-labeled autophagosomes with mitochondria, suggesting that calcitriol effectively promoted ethanol-induced mitophagy in hepatocytes. In addition, the inhibition of autophagy attenuated the protective and preventive effect of calcitriol. Furthermore, the effect of calcitriol on autophagy was regulated by AMPK/mTOR signaling, and signaling transduction was dependent on the Vitamin D receptor (VDR). In conclusion, calcitriol ameliorates ethanol-induced hepatocyte damage by enhancing autophagy. It may offer a convenient preventive and hepatoprotective mean for people on occasional social drink.

Studies on effects of static electric field exposure on liver in mice

With the development of ultra-high-voltage direct-current transmission, the intensity of static electric field (SEF) under transmission lines increased, which has aroused public attention on its potential health effects. In order to examine effects of SEF exposure on liver, institute of cancer research mice were exposed to SEF with intensities of 27.5 kV/m, 34.7 kV/m and 56.3 kV/m, respectively. In each intensity of SEF exposure, a corresponding sham exposure group was used. Several indices relating to liver function (aspartate aminotransferase (AST) and alanine aminotransferase (ALT)) and oxidative stress (superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA)) were tested after exposure of 7, 14, 21 and 35 days. Results showed that exposure to SEF with intensities of 27.5 kV/m and 34.7 kV/m for 35 days did not significantly influence any detected indices above. Under SEF exposure with intensity of 56.3 kV/m, the SOD activity in liver was significantly increased after exposure of 7 and 14 days. However, no significant increase was found in MDA content as well as the activities of AST and ALT between exposure group and sham exposure group during SEF exposure of 56.3 kV/m. It suggested that from three SEF intensities, only exposure to SEF with intensity of 56.3 kV/m (7 and 14 days) caused a temporary oxidative stress response in liver expressed by the increase in activity of SOD, but it did not produce oxidative damage. This biological effect may be related to the increase of mitochondrial membrane potential of hepatocytes caused by SEF exposure. When the membrane potential exceeds a threshold, Q cycle in mitochondria will be affected, which will result in an increase of superoxide anion concentration and ultimately an oxidative stress.

Мембранний потенціал мітохондрій за дії сураміну

Відомо, що сурамін є агоністом ріанодинчутливих Са2+-каналів ендоплазматичного ретикулуму (RyRs). Ми припустили, що він може бути агоністом і мітохондріальних ріанодинчутливих Са2+-каналів (mRyRs). Для перевірки цього припущення досліджено зміни мембранного потенціалу мітохондрій гепатоцитів під впливом сураміну. Сурамін у концентрації 1 мкмоль/л додавали до середовища інкубації, після цього вносили суспензію ізольованих мітохондрій та реєстрували їхній мембранний потенціал. Вимірювання мембранного потенціалу мітохондрій здійснювали з використанням метилтрифенілфосфоніум броміду (ТРМР+) і чутливого до нього електрода. Для ініціації дихання вносили субстрати окиснення сукцинат, піруват або α-кетоглутарат у концентраціях 5 ммоль/л, а для стимуляції окисного фосфорилювання – 320 нмоль АДФ. Установлено, що ефект сураміну на мембранний потенціал мітохондрій залежить від наявності в середовищі інкубації субстратів окиснення та фосфорилювання. За окиснення екзогенного сукцинату під впливом сураміну мембранний потенціал мітохондрій у стані S4 за Чансом і Вільямсом (1955) зменшився на 5,88 % відносно контролю, що, можливо, спричинено використанням енергії мембранного потенціалу мітохондрій на транспортування іонів Са2+ у матрикс мітохондрій. За окиснення α-кетоглутарату сурамін спричиняв збільшення мембранного потенціалу мітохондрій у стані S4 на 15,2 %, а за окиснення пірувату – на 39,1 %, порівняно з контролем. Збільшення мембранного потенціалу мітохондрій у стані S4 під впливом сураміну за окиснення α-кетоглутарату й пірувату пов’язане, мабуть, з активацією α-кетоглутаратдегідрогеназного чи піруватдегідрогеназного комплексів, які, на відміну від сукцинатдегідрогенази, є Са2+-залежними ферментами. Отже, сурамін у концентрації 1 мкмоль/л, активуючи мітохондріальні ріанодинчутливі Са2+-каналів гепатоцитів щура, спричиняє збільшення надходження Са2+ у матрикс мітохондрій, активацію Са2+-залежних дегідрогеназ і збільшення мембранного потенціалу мітохондрій.

Aniline Induces Oxidative Stress and Apoptosis of Primary Cultured Hepatocytes.

The toxicity and carcinogenicity of aniline in humans and animals have been well documented. However, the molecular mechanism involved in aniline-induced liver toxicity and carcinogenesis remains unclear. In our research, primary cultured hepatocytes were exposed to aniline (0, 1.25, 2.50, 5.0 and 10.0 μg/mL) for 24 h in the presence or absence of N-acetyl-l-cysteine (NAC). Levels of reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH), activities of superoxide dismutase (SOD) and catalase (CAT), mitochondrial membrane potential, DNA damage, cell viability, and apoptosis were detected. Levels of ROS and MDA were significantly increased and levels of GSH and CAT, activity of SOD, and mitochondrial membrane potential in hepatocytes were significantly decreased by aniline compared with the negative control group. The tail moment and DNA content of the tail in exposed groups were significantly higher than those in the negative control group. Cell viability was reduced and apoptotic death was induced by aniline in a concentration-dependent manner. The phenomena of ROS generation, oxidative damage, loss of mitochondrial membrane potential, DNA damage and apoptosis could be prevented if ROS inhibitor NAC was added. ROS generation is involved in the loss of mitochondrial membrane potential and DNA injury, which may play a role in aniline-induced apoptosis in hepatocytes. Our study provides insight into the mechanism of aniline-induced toxicity and apoptosis of hepatocytes.

Modulation of Na+/Mg2+ exchanger stoichiometry ratio by Cl− ions in basolateral rat liver plasma membrane vesicles

The Na+/Mg²+ exchanger represents the main Mg²+ extrusion mechanism operating in mammalian cells including hepatocytes. We have previously reported that this exchanger, located in the basolateral domain of the hepatocyte, promotes the extrusion of intravesicular trapped Mg²+ for extravesicular Na+ with ratio 1. This electrogenic exchange is supported by the accumulation of tetraphenyl-phosphonium within the vesicles at the time when Mg²+ efflux occurs. In this present study, the role of extra- and intra-vesicular Cl⁻ on the Na+/Mg²+ exchange ratio was investigated. The results reported here suggest that Cl⁻ ions are not required for the Na+ to Mg²+ exchange to occur, but the stoichiometry ratio of the exchanger switches from electrogenic (1Na(in)+ :1Mg(out)²+) in the presence of intravesicular Cl⁻ to electroneutral (2Na(in)+ :1 Mg(out)²+) in their absence. In basolateral liver plasma membrane vesicles loaded with MgCl₂ labeled with ³⁶Cl⁻, a small but significant Cl⁻ efflux (~30 nmol Cl⁻/mg protein/1 min) is observed following addition of NaCl or Na-isethionate to the extravesicular medium. Both Cl⁻ and Mg²+ effluxes are inhibited by imipramine but not by amiloride, DIDS, niflumic acid, bumetanide, or furosemide. In vesicles loaded with Mg-gluconate and stimulated by Na-isethionate, an electroneutral Mg²+ extrusion is observed. Taken together, these results suggest that the Na+/Mg²+ exchanger can operate irrespective of the absence or the presence of Cl⁻ in the extracellular or intracellular environment. Changes in trans-cellular Cl⁻ content, however, can affect the modus operandi of the Na+/Mg²+ exchanger, and consequently impact "cellular" Na+ and Mg²+ homeostasis as well as the hepatocyte membrane potential.

Mitochondria-Associated Hbv x Antigen: What is Going On?

Evaluation of: Clippinger AJ, Bouchard MJ: Hepatitis B virus HBx protein localizes to mitochondria in primary rat hepatocytes and modulates mitochrondrial membrane potential. J. Virol. 82(14), 6798–6811 (2008). Over 350 million people are chronically infected with HBV, and a significant number of these individuals develop primary liver cancer. HBV encodes seven viral proteins, including the nonstructural Hepatitis B x (HBx) protein. The results of studies with immortalized or transformed cells and with HBx transgenic mice demonstrated that HBx can interact with mitochondria. However, no studies with normal hepatocytes have characterized the precise mitochondrial localization of HBx or the effect of HBx on mitochondrial physiology. We have used cultured primary rat hepatocytes as a model system to characterize the mitochondrial localization of HBx and the effect of HBx expression on mitochondrial physiology. We now show that a fraction of HBx co-localizes with density gradient-purified mitochondria and associates with the outer mitochondrial membrane. We also demonstrate that HBx regulates mitochondrial membrane potential in hepatocytes, and that this function of HBx varies depending upon the status of NF-κB activity. In primary rat hepatocytes, HBx activation of NF-κB prevented mitochondrial membrane depolarization; however, when NF-κB activity was inhibited, HBx induced membrane depolarization through modulation of the mitochondrial permeability transition pore. Collectively, these results define potential pathways through which HBx may act in order to modulate mitochondrial physiology, thereby altering many cellular activities and ultimately contributing to the development of HBV-associated liver cancer.

Glutamine attenuates the production of nitric oxide production and the reduction of mitochondrial membrane potential of cultured rat hepatocytes induced by IL-1β

Objective To investigate the effects of different concentrations of glutnine(Gln) on the procfion of nitric oxide (NO)and reduction in mitochondrial membrane potential in rat heputocytes activated in by interleukin(IL)-1β.Method The primary cultured rat hepatocytes with high-purity Wfffe isolated from 6-week-old male Sprague-Dawley raL, by flirt in situ circulatory collagenase peffusion method.After incubation for hours.hepatocytes were stimulated by saline,or IL-l(1 nmol/L)or IL-I(1 mnol/L)combined with gIne in concentrations rangiIfrom 2 to 10 mmol/L.The culture muln and hepatocytes were collected at 24 hours after stimulation.The concentrations of alanine aminotransferase(ALT)and NO in the lnllln were detected by biochemical methods.The mitochondrial membrane potential of the hepatocytes was detected with flow cytometry after incubated with fluorescem probe JC-1.Statistic package ofSPSS 11.5 was used for the data analysand significant differences between mean8 were evaluated byQ、4k analysis.Results The average concentration ofand NOinthe culturemedium afterIL-Istimulationwas 38.2U/L and 72.7tmaol/L,respectively,whichwere sis,cantly big,herthanthose ofcontrol group(7.4 U/L and41.7nol/L,respectively,P<0.01).1hemitochondrial membrane potential ofhepatocytes in IL-lgroup was much lowerthan that in control group(30.O%vs.62.8%.P<0.01).Gin inhibited NO production induced byⅡ,lp,Jeleasing and reduction in mitochondrial II brahetential ofcuhured rat hepatocytes in a dose-dependent HmIll.Conclusions Ghtamine,the most abundant free amino acid in the body,call attenuate hepatocye injury mechateel in vitro by pro-inflammatory cytokine mediated.nlis protective effectmay be associatedwiththeinhibition of NO production and thereby amelioration of mitochondrialfunction. Key words: Glutamine; Hepatocyte; Mitochondria membrane potential; IL-I; Nitric oxide

Hepatitis B virus HBx protein localizes to mitochondria in primary rat hepatocytes and modulates mitochondrial membrane potential.

Over 350 million people are chronically infected with hepatitis B virus (HBV), and a significant number of chronically infected individuals develop primary liver cancer. HBV encodes seven viral proteins, including the nonstructural X (HBx) protein. The results of studies with immortalized or transformed cells and with HBx-transgenic mice demonstrated that HBx can interact with mitochondria. However, no studies with normal hepatocytes have characterized the precise mitochondrial localization of HBx or the effect of HBx on mitochondrial physiology. We have used cultured primary rat hepatocytes as a model system to characterize the mitochondrial localization of HBx and the effect of HBx expression on mitochondrial physiology. We now show that a fraction of HBx colocalizes with density-gradient-purified mitochondria and associates with the outer mitochondrial membrane. We also demonstrate that HBx regulates mitochondrial membrane potential in hepatocytes and that this function of HBx varies depending on the status of NF-kappaB activity. In primary rat hepatocytes, HBx activation of NF-kappaB prevented mitochondrial membrane depolarization; however, when NF-kappaB activity was inhibited, HBx induced membrane depolarization through modulation of the mitochondrial permeability transition pore. Collectively, these results define potential pathways through which HBx may act in order to modulate mitochondrial physiology, thereby altering many cellular activities and ultimately contributing to the development of HBV-associated liver cancer.

Glucagon activates Ca2+ and Cl− channels in rat hepatocytes

Glucagon is one of the major hormonal regulators of glucose metabolism, counteracting the hepatic effects of insulin when the concentration of glucose in the bloodstream falls below a certain level. Glucagon also regulates bile flow, hepatocellular volume and membrane potential of hepatocytes. It is clear that changes in cell volume and membrane potential cannot occur without significant ion fluxes across the plasma membrane. The effects of glucagon on membrane currents in hepatocytes, however, are not well understood. Here we show, by patch-clamping of rat hepatocytes, that glucagon activates two types of currents: a small inwardly rectifying Ca2+ current with characteristics similar to those of the store-operated Ca2+ current and a larger outwardly rectifying Cl- current similar to that activated by cell swelling. We show that the mechanism of glucagon action on membrane conductance involves phospholipase C and adenylyl cyclase. Contribution of the adenylyl cyclase-dependent pathway to activation of the currents depended on Epac (exchange protein directly activated by cAMP), but not on protein kinase A. The activation of Ca2+ and Cl- channels is likely to play a key role in the mechanisms by which glucagon regulates hepatocyte metabolism and volume.

Hyperpolarization of hepatocyte membrane potential and inhibition of cell growth by stable transfection with GABAA β3 subunit : Dongfeng Sun, Gerald Y Minuk, University of Manitoba, Winnipeg, MB Canada

Hyperpolarization of hepatocyte membrane potential and inhibition of cell growth by stable transfection with GABAA β3 subunit : Dongfeng Sun, Gerald Y Minuk, University of Manitoba, Winnipeg, MB Canada

The effects of various organ preservation solutions on hepatocyte membrane potentials, intracellular calcium concentrations, and outcome following liver transplantation

Background: Hepatocyte membrane potential differences (PDs) may be altered by the preservation solutions used in liver transplantation. Such alterations could impact on the survival of the donor liver, extent of biochemical injury, and flux of important ionic compounds. The purpose of the present study was to document these outcomes in the presence of four different preservation solutions. Methods: Livers of adult male Sprague-Dawley rats (N = 3 to 4 per group) were impaled with intracellular microelectrodes prior to and at various time periods for 6 hours following complete hepatic resection. Just prior to resection, each liver was perfused with preservation solutions associated with high (normal saline [NS]), moderate (Euro-Collins [EC]), and low (University of Wisconsin solution [UW]) risks of reperfusion injury. Results: Baseline (in situ) PDs were similar in all groups (−37 ± 4 mV, mean ± SD). Ten minutes postresection, hepatic PDs were as follows: NS, −23.8 ± 3.5 mV; EC, −11.4 ± 0.4 mV; and UW, −8.7 ± 0.3 mV ( P <0.01 for all groups). Maximum depolarization occurred at 6 hours postresection (NS, −8.1 ± 1.1 mV; EC, −7.7 ± 1.3 mV; and UW, −8.6 ± 1.0 mV). To determine whether these changes are of pathophysiologic importance, the NS solution was modified (addition of 0.1% ethanol) to achieve similar PD changes as those observed with UW. Liver transplants were then performed where the donor livers had been perfused and preserved for 6 hours with either NS or the modified NS (MNS) solution. Posttransplant (10 day) survival was 1 of 6 (17%) in the NS group and 4 of 6 (67%) in the MNS group ( P <0.05). Regarding the effects of PD changes on ionic flux, intracellular calcium levels were documented for up to 4 hours by fluorescence video microscopy using Fura-2 in isolated hepatocytes exposed to NS, UW, and MNS solutions. Intracellular calcium levels were similar in all solutions at each time point studied. Conclusions: The results of this study indicate that hepatocytes undergo prompt and marked depolarization following hepatic resection, and the extent of the depolarization correlates with survival following transplantation.

2-Mercaptoacetate, an inhibitor of fatty acid oxidation, decreases the membrane potential in rat liver in vivo.

In former work, intraperitoneal injection of 2-mercaptoacetate (MA), an inhibitor of fatty acid oxidation, increased food intake in rats, which was attenuated by hepatic branch vagotomy, and intraportal injection of MA increased the discharge rate in hepatic vagal afferents. In the present study, we investigated, whether intraperitoneal injection or intraportal infusion of MA affects the hepatic membrane potential in rats in vivo. The liver cell membrane potential was measured in anesthetized Sprague-Dawley rats with the microelectrode technique. Intraperitoneal injection of MA at a dose of 800 micromol/kg body wt significantly decreased the hepatocyte membrane potential by 3.8 mV, whereas at a dose of 400 micromol/kg, the depolarization (1.5 mV) of the membrane was not significant. In another strain of Sprague-Dawley rats, however, MA (400 micromol/kg) produced a significant depolarization of the hepatocyte membrane 50 min (2.6 mV) and 2 h (2.9 mV) after intraperitoneal injection. Intraportal infusion of MA (400 micromol/kg) significantly depolarized the membrane 20 and 50 min after infusion by 3.3 and 4.1 mV, respectively. MA at a dose of 800 micromol/kg also depolarized the membrane (4.8 mV after 50 min). These findings in principle are consistent with the "potentiostatic" hypothesis, postulating a link between the hepatic membrane potential, afferent vagal activity, and the control of food intake.

The effect of changes in hepatocyte membrane potential on immediate-early proto-oncogene expression following partial hepatectomy in rats.

The stimulus responsible for inducing hepatocytes to enter the cell cycle following partial hepatectomy (PHx) remains to be identified. One suggested candidate is the change in hepatocyte membrane potential (PD) that occurs immediately following PHx. To test this possibility, we monitored changes in hepatocyte PD and immediate-early proto-oncogene expression in rats pretreated with saline or gamma aminobutyric acid (GABA), an amino-acid neurotransmitter that hyperpolarizes isolated hepatocytes. Intraperitoneal injections of saline or GABA (500 microg/g body weight) were administered to adult, male Sprague-Dawley rats 1 hour prior to 70% PHx. Rats were sacrificed and the livers excised at various times until 180 minutes post-PHx for messenger RNA (mRNA) and protein analyses. In additional groups of saline- and GABA-treated rats, PD changes were recorded continuously from -260 to 180 minutes post-PHx. Serum GABA concentrations were determined by ion-exchange chromatography with orthopthaldehyde fluorescence detection. Hepatocyte PD's were recorded in situ by intracellular microelectrodes with an Axoprobe-1A amplifier. Steady-state levels of c-fos, c-jun, jun-B, and c-myc transcripts and proteins were documented by Northern blots of poly(A)-enriched RNA derived from resected livers and Western blots of total nuclear protein, respectively. Serum GABA concentrations remained unchanged in saline-treated controls but increased 10- to 20-fold above baseline values in GABA-treated rats. In saline-treated controls, hepatocyte depolarization occurred immediately and was maintained throughout the 180 minutes post-PHx period (PD pre-PHx, -36.8 +/- 5.1; 15 minutes post-PHx, -27.5 +/- 5.7; and 180 minutes post-PHx, -28.3 +/- 4.4 mV, mean +/- SD); whereas in GABA-treated rats, hepatocyte PD remained unchanged (-37.0 +/- 1.1; -36.4 +/- 3.1 and -39.2 +/- 2.7 mV, respectively). Despite abrogation of hepatocyte PD changes, proto-oncogene mRNA and protein levels in saline- and GABA-treated rats were either similar or, in the case of c-fos and c-jun, increased five- to sevenfold in GABA-treated rats. The results of this study indicate the following: 1) hepatocytes depolarize immediately post-PHx and remain depolarized throughout the priming phase of the cell cycle; 2) elevated serum GABA concentrations prevent PHx-induced hepatocyte depolarization; and 3) depolarization is not the stimulus responsible for priming hepatocytes into replicative competence.

Role of the liver in the metabolic control of eating: What we know—and what we do not know

Profound meal-related changes in the supply of metabolites to the liver and in hepatic metabolism occur, and there is ample evidence that neural signals from hepatic metabolic sensors can affect eating. Hepatic afferent nerves presumably represent glucosensors which contribute to the control of eating by monitoring their own glucose utilization. Yet, the nature of the putative sensors that respond to the oxidation of other metabolites than glucose has not been identified. ATP and sodium pump activity may link hepatic oxidative metabolism and membrane potential, because hepatic phosphate-trapping by 2,5-anhydro-mannitol, and inhibition of sodium pump activity by ouabain is associated with a stimulation of eating. Hepatocyte membrane potential is also subject to changes in transmembranal potassium flow through volumetrically controlled membranal potassium channels. Yet it is unknown if and how hepatocytes are linked to afferent nerves. It is also unclear how the effects of glucagon and insulin fit into the hepatic metabolic control of eating. Glucagon appears to induce satiety through its actions in the liver, but the involved mechanism is still unclear. Recent studies suggest that insulin, which has mainly been explored as a centrally acting long-term satiety signal, has an immediate effect on meal size, but it is presently unknown whether an hepatic action of insulin is involved.

Hyperpolarization of the liver cell membrane by palmitate as affected by glucose and lactate: Implications for control of feeding

Since the membrane potential of liver cells being in contact with vagal afferents has been proposed to represent a major signal in metabolic control of food intake, we investigated the effect of palmitate, glucose and lactate on the membrane potential of hepatocytes with microelectrodes using superfused mouse liver slices. The mice used for the experiments were fed a fat-enriched diet (18% fat). Palmitate (0.5 mM) hyperpolarized the membrane of hepatocytes by 3–4 mV, and this hyperpolarization was not affected by 5–10 mM glucose and 0.5–1 mM lactate. Glucose alone did not influence the potential, even when mice fed a high carbohydrate diet were employed. At lactate concentrations ≥ 2 mM the palmitate induced hyperpolarization was eliminated and 5 mM lactate or pyruvate alone hyperpolarized the liver cell membrane. Similar to the palmitate induced hyperpolarization, the lactate induced hyperpolarization was prevented by the K-channel blocker TEA, suggesting that activation of K channels is involved in the hyperpolarization. The results show that physiological concentrations of glucose and lactate do not affect the hyperpolarization of the liver cell membrane due to fatty acid oxidation. The implications of these findings with regard to control of food intake by fatty acid oxidation and lactate metabolism are discussed. The observations are consistent with a signal function of the hepatic membrane potential in physiological control of food intake by fatty acid oxidation. Hepatic lactate metabolism at supraphysiological lactate concentrations may also produce a satiety signal coded by the hepatic membrane potential.

Causes of differences in respiration rate of hepatocytes from mammals of different body mass.

Resting O2 consumption of hepatocytes isolated from mammals ranging in mass from 20-g mice to 200-kg horses decreases with increasing body mass. The substrate oxidation system increases in activity with increasing body mass and mitochondrial proton leak and phosphorylation system decrease in activity, resulting in a higher mitochondrial membrane potential in hepatocytes from larger mammals. The absolute rates of O2 consumption due to nonmitochondrial processes, substrate oxidation, mitochondrial proton leak, and the phosphorylation system decrease with increasing body mass. These decreases are due partly to a decrease in mitochondrial number per cell and partly to decrease in mitochondrial inner membrane proton leakiness and in ATP turnover by cells from larger mammals. Quantitatively, the proportion of total cell O2 consumption by nonmitochondrial processes (13%) and oxidation of substrates (87%) and the proportions used to drive mitochondrial proton leak (19%) and the phosphorylation system (68%) are the same for hepatocytes from all mammals investigated. The effect of matched decreases in the rates of proton leak and of ATP turnover is to keep the effective amount of ATP synthesized per unit of O2 consumed relatively constant with body mass, suggesting that the observed value is optimal.

Membrane potential of hepatocytes in intact and those isolated from normal and cirrhotic animals: [formula omitted] Departments of Medicine and Pharmacology 2, University of Manitoba, Winnipeg, Canada

Membrane potential of hepatocytes in intact and those isolated from normal and cirrhotic animals: [formula omitted] Departments of Medicine and Pharmacology 2, University of Manitoba, Winnipeg, Canada