Modifications of intracellular calcium release channels and calcium mobilization following 70% hepatectomy

Blood flow-bearing physical forces, endothelial glycocalyx, and liver enzyme mobilization: A hypothesis

Numerous elements involved in shear stress-induced signaling have been identified, recognizing their functions as mechanotransducing ion channels situated at cellular membranes. This form of mechanical signaling relies on transmembrane proteins and cytoplasmic proteins that restructure the cytoskeleton, contributing to mechanotransduction cascades. Notably, blood flow generates mechanical forces that significantly impact the structure and remodeling of blood vessels. The primary regulation of blood vessel responses occurs through hemodynamic forces acting on the endothelium. These mechanical events intricately govern endothelial biophysical, biochemical, and genetic responses. Endothelial cells, positioned on the intimal surface of blood vessels, have the capability to express components of the glycocalyx. This endothelial structure emerges as a pivotal factor in mechanotransduction and the regulation of vascular tone. The endothelial glycocalyx assumes diverse roles in both health and disease. Our findings propose a connection between the release of specific enzymes from the rat liver and variations in the hepatic blood flow/mass ratio. Importantly, this phenomenon is not correlated with liver necrosis. Consequently, this review serves as an exploration of the potential involvement of membrane proteins in a hypothetical mechanotransducing phenomenon capable of controlling the release of liver enzymes.

Calcium transfer between endoplasmic reticulum and mitochondria in liver diseases

Calcium (Ca²⁺ ) is a second messenger essential for cellular homeostasis. Inside the cell, Ca²⁺ is compartmentalized and exchanged among organelles in response to both external and internal stimuli. Mitochondria-associated membranes (MAMs) provide a platform for proteins and channels involved in Ca²⁺ transfer between the endoplasmic reticulum (ER) and mitochondria. Deregulated Ca²⁺ signaling and proteins regulating ER-mitochondria interactions have been linked to liver diseases and intensively investigated in recent years. In this review, we summarize the role of MAM-resident proteins in Ca²⁺ transfer and their association with different liver diseases.

Involvement of cell oxidant status and redox state in the increased non-enzymatic ethanol oxidation by the regenerating rat liver

Ethanol administration is capable of inhibiting or delaying the partial hepatectomy (PH)-induced liver regeneration, probably altering liver metabolism by means of its oxidative metabolism. Since the regenerating liver has increased capacity for oxidizing ethanol, the present study was aimed to address the contribution of the ethanol-oxidizing metabolic pathways in the regenerating liver cells. Isolated hepatocytes were prepared from control livers and from animals subjected to two-thirds PH. In both preparations, ethanol oxidation was largely increased by incubation with glucose and was highly sensitive to inhibitors of ethanol-oxidizing enzymatic pathways (alcohol dehydrogenase, catalase and cytochrome P-4502E1 activities). The latter led to a total blockade of ethanol disposal by control hepatocytes, while liver cells from PH-rats only showed an early 70-75% inhibition of ethanol catabolism with the inhibitors used. In regenerating hepatocytes, the enhanced ethanol oxidation was blocked by scavengers of reactive oxygen species, an effect that correlated with enhanced cytoplasmic lipid peroxidation by-products. Both cell preparations showed similar sensitivity to inhibitors for the malate-aspartate shuttle and mitochondrial electron transport chain; the shift of the cytoplasmic redox state was also quite similar after ethanol oxidation. A more oxidized mitochondrial redox state was found in hepatocytes from PH-rats and more shifted to the reduced state during ethanol oxidation this effect was not abolished by inhibiting alcohol dehydrogenase activity. In conclusion, data clearly show that an important fraction of ethanol is metabolized through a non-enzymatic-mediated oxidative event, which could largely contribute to the deleterious effect of ethanol on the proliferating liver.

High α-tocopherol dosing increases lipid metabolism by changing redox state in damaged rat gastric mucosa and liver after ethanol treatment

Regeneration of ethanol-injured rat gastric mucosa must undergo changes in major metabolic pathways to achieve DNA replication and cell proliferation. These events are highly dependent on glucose utilization and inhibited by vitamin E (VE) (α-tocopherol) administration. Therefore, the present study aimed at assessing lipid metabolism in the gastric mucosa and ethanol-induced gastric damage and the effect of α-tocopherol administration. For this, rates of fatty acid β-oxidation and lipogenesis were tested in gastric mucosa samples. Through histological analysis, we found loss of the mucosa's superficial epithelium, which became gradually normalized during the recovery period. Proliferation of gastric mucosa occurred with augmented formation of β-oxidation by-products, diminished synthesis of triacylglycerols (TGs), as well as of phospholipids, and a reduced cytoplasmic NAD/NADH ratio, whereas the mitochondrial redox NAD/NADH ratio was much less affected. In addition, α-tocopherol increased palmitic acid utilization in the gastric mucosa, which was accompanied by the induction of 'mirror image' effects on the cell redox state, reflected in an inhibited cell gastric mucosa proliferation by the vitamin administration. In conclusion, the present study shows, for the first time, the role of lipid metabolism in the adaptive cell gastric mucosa changes that drive proliferation after a chronic insult. Moreover, α-tocopherol increased gastric mucosa utilization of palmitic acid associated with energy production. These events could be associated with its antioxidant properties in co-ordination with regulation of genes and cell pathways, including changes in the cell NAD/NADH redox state.

Rat Liver Enzyme Release Depends on Blood Flow-Bearing Physical Forces Acting in Endothelium Glycocalyx rather than on Liver Damage

We have found selective elevation of serum enzyme activities in rats subjected to partial hepatectomy (PH), apparently controlled by hemodynamic flow-bearing physical forces. Here, we assess the involvement of stretch-sensitive calcium channels and calcium mobilization in isolated livers, after chemical modifications of the endothelial glycocalyx and changing perfusion directionality. Inhibiting in vivo protein synthesis, we found that liver enzyme release is influenced by de novo synthesis of endothelial glycocalyx components, and released enzymes are confined into a liver “pool.” Moreover, liver enzyme release depended on extracellular calcium entry possibly mediated by stretch-sensitive calcium channels, and this endothelial-mediated mechanotransduction in liver enzyme release was also evidenced by modifying the glycocalyx carbohydrate components, directionality of perfusing flow rate, and the participation of nitric oxide (NO) and malondialdehyde (MDA), leading to modifications in the intracellular distribution of these enzymes mainly as nuclear enrichment of “mitochondrial” enzymes. In conclusion, the flow-induced shear stress may provide fine-tuned control of released hepatic enzymes through mediation by the endothelium glycocalyx, which provides evidence of a biological role of the enzyme release rather to be merely a biomarker for evaluating hepatotoxicity and liver damage, actually positively influencing progression of liver regeneration in mammals.

Characteristics of intracellular Ca2+ signals consisting of two successive peaks in hepatocytes during liver regeneration after 70% partial hepatectomy in rats

Two specific signals for regulating liver regeneration were found after 70% partial hepatectomy (PH) in rats. The first finding was a sustained increasing signal of intracellular Ca²⁺ ([Ca²⁺]_i) in hepatocytes, consisting of two successive peaks with the first narrow peak at 1 hour and the second broad peak increasing by day 3 and then returning to normal by day 4. The second finding was an abnormal peak in the restoring ratio (R_r) curve of liver regeneration after 70% PH at day 4, where the R_r exceeded 100% temporarily, returned to a lower level, and then proceeded to a termination phase of liver regeneration. For 4 days around the two successive [Ca²⁺]_i peaks and abnormal peak, various physiological activities were induced to promote liver regeneration after 70% PH. mRNA expression of genes encoding Ca²⁺-binding proteins S100A4 and calpain was induced between the two Ca²⁺ peaks. Hepatocytes underwent synchronous cell proliferation as the liver was restored from 30% to 70% at day 4, and significant expression of VEGF mRNA at around day 4 promoted angiogenesis to remodel the sinusoidal system. Cytochrome P450 activity levels in microsomes and alanine aminotransferase values at 24 hours after CCl₄ administration were decreased after 70% PH, which recovered transiently to the control level at day 4, returned to the decreased level, and then slowly recovered by day 10. Thus, these results indicate that day 4 is important during liver regeneration after 70% PH.

A novel, dynamic pattern-based analysis of NF-κB binding during the priming phase of liver regeneration reveals switch-like functional regulation of target genes

Following partial hepatectomy, a coordinated series of molecular events occurs to regulate hepatocyte entry into the cell cycle to recover lost mass. In rats during the first 6 h following resection, hepatocytes are primed by a tightly controlled cytokine response to prepare hepatocytes to begin replication. Although it appears to be a critical element driving regeneration, the cytokine response to resection has not yet been fully characterized. Specifically, the role of one of the key response elements to cytokine signaling (NF-κB) remains incompletely characterized. In this study, we present a novel, genome-wide, pattern-based analysis characterizing NF-κB binding during the priming phase of liver regeneration. We interrogated the dynamic regulation of priming by NF-κB through categorizing NF-κB binding in different temporal profiles: immediate sustained response, early transient response, and delayed response to partial hepatectomy. We then identified functional regulation of NF-κB binding by relating the temporal response profile to differential gene expression. We found that NF-κB bound genes govern negative regulation of cell growth and inflammatory response immediately following hepatectomy. NF-κB also transiently regulates genes responsible for lipid biosynthesis and transport as well as induction of apoptosis following hepatectomy. By the end of the priming phase, NF-κB regulation of genes involved in inflammatory response, negative regulation of cell death, and extracellular structure organization became prominent. These results suggest that NF-κB regulates target genes through binding and unbinding in immediate, transient, and delayed patterns. Such dynamic switch-like patterns of NF-κB binding may govern different functional transitions that drive the onset of regeneration.

Calcium signaling in the liver

Intracellular free Ca(2+) ([Ca(2+)]i) is a highly versatile second messenger that regulates a wide range of functions in every type of cell and tissue. To achieve this versatility, the Ca(2+) signaling system operates in a variety of ways to regulate cellular processes that function over a wide dynamic range. This is particularly well exemplified for Ca(2+) signals in the liver, which modulate diverse and specialized functions such as bile secretion, glucose metabolism, cell proliferation, and apoptosis. These Ca(2+) signals are organized to control distinct cellular processes through tight spatial and temporal coordination of [Ca(2+)]i signals, both within and between cells. This article will review the machinery responsible for the formation of Ca(2+) signals in the liver, the types of subcellular, cellular, and intercellular signals that occur, the physiological role of Ca(2+) signaling in the liver, and the role of Ca(2+) signaling in liver disease.

Diurnal and nutritional adjustments of intracellular Ca2+ release channels and Ca2+ ATPases associated with restricted feeding schedules in the rat liver

Background

Intracellular calcium is a biochemical messenger that regulates part of the metabolic adaptations in the daily fed-fast cycle. The aim of this study was to characterize the 24-h variations of the liver ryanodine and IP₃ receptors (RyR and IP₃R) as well as of the endoplasmic-reticulum and plasma-membrane Ca²⁺-ATPases (SERCA and PMCA) in daytime restricted feeding protocol.

Methods

A biochemical and immunohistochemical approach was implemented in this study: specific ligand-binding for RyR and IP₃R, enzymatic activity (SERCA and PMCA), and protein levels and zonational hepatic-distribution were determined by immunoblot and immunohistochemistry respectively under conditions of fasting, feeding, and temporal food-restriction.

Results

Binding assays and immunoblots for IP₃R1 and 2 showed a peak at the light/dark transition in the ad-libitum (AL) group, whereas in the restricted-feeding (RF) group the peak shifted towards the food-access time. In the case of RyR binding experiments, both AL and RF groups showed a modest elevation during the dark period, with the RF rats exhibiting increased binding in response to feeding. The AL group showed 24-h rhythmicity in SERCA level; in contrast, RF group showed a pronounced amplitude elevation and a peak phase-shift during the light-period in SERCA level and activity. The activity of PMCA was constant along day in both groups; PMCA1 levels showed a 24-h rhythmicity in the RF rats (with a peak in the light period), meanwhile PMCA4 protein levels showed rhythmicity in both groups. The fasted condition promoted an increase in IP₃R binding and protein level; re-feeding increased the amount of RyR; neither the activity nor expression of SERCA and PMCA protein was affected by fasting–re-feeding conditions. Histochemical experiments showed that the distribution of the Ca²⁺-handling proteins, between periportal and pericentral zones of the liver, varied with the time of day and the feeding protocol.

Conclusions

Our findings show that RF influences mainly the phase and amplitude of hepatic IP₃R and SERCA rhythms as well as discrete zonational distribution for RyR, IP₃Rs, SERCA, and PMCA within the liver acinus, suggesting that intracellular calcium dynamics could be part of the rheostatic adaptation of the liver due to diurnal meal entrainment/food entrained oscillator expression.

Calcium signalling and liver regeneration

After partial hepatectomy (PH) the initial mass of the organ is restored through a complex network of cellular interactions that orchestrate both proliferative and hepatoprotective signalling cascades. Among agonists involved in this network many of them drive Ca(2+) movements. During liver regeneration in the rat, hepatocyte cytosolic Ca(2+) signalling has been shown on the one hand to be deeply remodelled and on the other hand to enhance progression of hepatocytes through the cell cycle. Mechanisms through which cytosolic Ca(2+) signals impact on hepatocyte cell cycle early after PH are not completely understood, but at least they include regulation of immediate early gene transcription and ERK and CREB phosphorylation. In addition to cytosolic Ca(2+), there is also evidence that mitochondrial Ca(2+) and also nuclear Ca(2+) may be critical for the regulation of liver regeneration. Finally, Ca(2+) movements in hepatocytes, and possibly in other liver cells, not only impact hepatocyte progression in the cell cycle but more generally may regulate cellular homeostasis after PH.

The role of calcium and nitric oxide during liver enzyme release induced by increased physical forces as evidenced in partially hepatectomized rats

Although increased plasma enzyme activities could be diagnostic for tissue damage, the mechanisms controlling cellular enzyme release remain poorly understood. We found a selective and drastic elevation of serum enzyme activities accompanying rat liver regeneration after partial hepatectomy (PH), apparently controlled by a mechanism dependent on flow-bearing physical forces. In fact, this study assesses a putative role of calcium mobilization and nitric oxide (NO) production underlying rat liver enzyme release. The role of increased shear stress (by enhancing viscosity during perfusion) and the participation of cell calcium and NO were tested in isolated livers subjected to increasing flow rate. After PH, there was a drastic elevation of serum activities for liver enzyme markers, clearly predominating those of mitochondrial localization. Liver enzyme release largely depended on extracellular calcium entry, probably mediated by stretch-sensitive calcium channels, as well as by increasing NO production. However, these effects were differentially observed when comparing liver enzymes from cytoplasmic or mitochondrial compartments. Moreover, a possible role for cell-mediated mechanotransduction in liver enzyme release was suggested by increasing shear stress (high viscosity), which also selectively affected the release of the enzymes tested. Therefore, we show, for the first time, that flow-induced shear stress can control the amount of hepatic enzymes released into the bloodstream, which is largely regulated through modifications in cell calcium mobilization and production of liver NO, events markedly elevated in the proliferating rat liver.

Mice Lackingbi-1Gene Show Accelerated Liver Regeneration

The liver has enormous regenerative capacity such that, after partial hepatectomy, hepatocytes rapidly replicate to restore liver mass, thus providing a context for studying in vivo mechanisms of cell growth regulation. Bax inhibitor-1 (BI-1) is an evolutionarily conserved endoplasmic reticulum (ER) protein that suppresses cell death. Interestingly, the BI-1 protein has been shown to regulate Ca(2+) handling by the ER similar to antiapoptotic Bcl-2 family proteins. Effects on cell cycle entry by Bcl-2 family proteins have been described, prompting us to explore whether bi-1-deficient mice display alterations in the in vivo regulation of cell cycle entry using a model of liver regeneration. Accordingly, we compared bi-1(+/+) and bi-1(-/-) mice subjected to partial hepatectomy with respect to the kinetics of liver regeneration and molecular events associated with hepatocyte proliferation. We found that bi-1 deficiency accelerates liver regeneration after partial hepatectomy. Regenerating hepatocytes in bi-1(-/-) mice enter cell cycle faster, as documented by more rapid incorporation of deoxynucleotides, associated with earlier increases in cyclin D1, cyclin D3, cyclin-dependent kinase (Cdk) 2, and Cdk4 protein levels, more rapid hyperphosphorylation of retinoblastoma protein, and faster degradation of p27(Kip1). Dephosphorylation and nuclear translocation of nuclear factor of activated T cells 1 (NFAT1), a substrate of the Ca(2+)-sensitive phosphatase calcineurin, were also accelerated following partial hepatectomy in BI-1-deficient hepatocytes. These findings therefore reveal additional similarities between BI-1 and Bcl-2 family proteins, showing a role for BI-1 in regulating cell proliferation in vivo, in addition to its previously described actions as a regulator of cell survival.

Remodelling of calcium signalling during liver regeneration in the rat

BACKGROUND/AIMS

During liver regeneration, a network of cytokines and growth factors interact with hepatocytes, helping to restore the liver mass and functions after partial tissue loss. Agonists that trigger Ca2+ signals in the liver contribute to this process, although little is known about calcium signalling during liver regeneration.

RESULTS

We observed two phases in which the hepatocyte response to calcium-mobilising agonists was greatly reduced versus control cells at 24h and five days after partial hepatectomy. We found that both phases of hepatocyte desensitisation involved the down-regulation of cell surface receptors and the type II InsP3 receptor. Single cell studies with flash photolysis of caged InsP3 revealed that InsP3-mediated Ca2+ release was slower in regenerating hepatocytes at 24, 48 h and 5 days than in control cells. Also, the temporal pattern of vasopressin-elicited intracellular calcium oscillations studied on fura2-loaded cells was altered, with the duration of each Ca2+ peak being longer. Finally, we showed an association between hepatocyte desensitisation and progression through the cell cycle towards the S phase at 24 h after hepatectomy.

CONCLUSIONS

Our study supports the remodelling of hepatocyte calcium signalling during liver regeneration, and that this change is partly linked with cell cycle progression.

Differential change of Ins-P3-Ca2+ signaling during culture of rat hepatocytes

Decrease of alpha-adrenergic responses during primary culture of rat hepatocytes was studied. Activation of glycogen phosphorylase by phenylephrine was decreased in the early stage of the culture (within 6 h), however, Ins-P3 production was almost intact until 12 h of the culture and then declined. alpha-Adrenoceptor-mediated Ca2+-mobilization and Ins-P3-induced Ca2+ release from microsomal fractions were decreased in the early stage of the culture, similar to the above change of phosphorylase activation. We found that decrease of Ins-P3-binding sites in the early stage of the culture was the cause of differential change of Ins-P3-Ca2+ signaling during the culture of hepatocytes. Similar changes described above were also observed in vasopressin-induced responses. However, the changes of Ins-P3-Ca2+ signaling did not occur in a high-cell density culture of rat hepatocytes. In conclusion, the loss of phenylephrine- and vasopressin-induced responses in cultured liver cells appear to be due to change of Ins-P3-binding sites as well as decreased Ins-P3 production due to reduction of receptor numbers.

Plasma membrane Ca2+-ATPase mRNA expression in murine hepatocarcinoma and regenerating liver cells

The plasma membrane calcium ATPase (PMCA) is an ubiquitous enzyme that extrudes calcium from the cytoplasm to the extracellular space. Four PMCA genes through alternative splicing produce a large diversity of isoforms of this enzyme. We reported previously that the PMCA contained in AS-30D hepatocarcinoma cells showed significant differences in activity in comparison to normal and regenerating liver. In the present study we investigate if the difference in PMCA activity could be related to differential expression of mRNAs encoding different isoforms of PMCA. Using RT-PCR we found that variants 1b, 1x, and 4b are expressed in all liver samples. The hepatoma AS-30 and liver at 2 days of regeneration express low amounts of isoforms 2w, 4b and 4x, and do not express isoforms 4a, 4d and 4z. Fetal and neonatal liver do not express variants 4a and 4d, but they do express variants 4x and 4z. Immunoblot analysis showed a higher ratio ATPase/total protein in the hepatoma AS-30D in comparison to normal liver. Our results suggest that the Ca2+-ATPase kinetic pattern previously observed by us in the AS-30D cells, could be at least partially explained by changes in the mRNA expression of several of the PMCA isoforms expressed in the liver.

Changes in mitochondrial adenine nucleotides and in permeability transition in two models of rat liver regeneration

Although enhanced phosphorylative activity can be a requisite for later DNA synthesis during liver regeneration (LR), mitochondrial generation of reactive oxygen species could lead to altered mitochondrial membrane permeability during the prereplicative phase of LR. Therefore, the role of mitochondrial permeability transition (MPT) was evaluated during rat LR, induced by either partial hepatectomy (PH) or after CCl(4) administration. Parameters indicative of mitochondrial function and membrane potentials, those of oxidative stress, and in vivo changes of the intramitochondrial pool of adenine nucleotides were determined. Twelve hours after PH, mitochondrial oxidative and phosphorylative activities and adenosine diphosphate (ADP) content were increased, reaching a maximal peak at 24 hours after surgery (maximal DNA synthesis). Parameters suggestive of oxidant stress were enhanced, but mitochondrial volume and membrane electrical potential remained unaltered. Interestingly, moderate mitochondrial swelling and depolarization were found at later post-PH times (72 hours). In CCl(4)-treated animals, it was found that an active liver cell necrosis delayed mitotic activity and mitochondrial uncoupled respiration. Starting 12 hours after CCl(4) intoxication, a drastic increase of inorganic phosphate occurred within swollen and strongly depolarized mitochondria, suggesting changes in the MPT. Despite expression of messenger RNA (mRNA) for mitochondrial transcription, factor A showed a similar time course in both experimental models. The so-called augmenter liver regeneration was found significantly elevated only in PH rats. In conclusion, onset of MPT could be associated with cell necrosis and inflammation after CCl(4) treatment, whereas this mitochondrial event could constitute a putative effector mechanism, through which growth or inflammatory factors inhibiting cell proliferation could initiate LR termination.

Enhanced intracellular calcium promotes metabolic and secretory disturbances in rat gastric mucosa during ethanol-induced gastritis

Changes in the Ca(2+) homeostasis have been implicated in cell injury and death. However, Ca(2+) participation in ethanol-induced chronic gastric mucosal injury has not been elucidated. We have developed a model of ethanol-induced chronic gastric injury in rats, characterized by marked alterations in plasma membranes from gastric mucosa and a compensatory cell proliferation, which follows ethanol withdrawal. Therefore, the present study explored the possible role of intracellular Ca(2+) in the oxidative metabolism and in acid secretion in this experimental model. Glucose oxidation was greatly enhanced in the injured mucosa, as evaluated by CO(2) production by isolated mucosal preparations incubated with (14)C-radiolabeled glucose in different carbons. Oxygen consumption and acid secretion (aminopyrine accumulation) were also stimulated. A predominating secretory status was morphologically identified by electron microscopy in oxyntic cells of gastric mucosa from ethanol-treated rats. A coupling between secretory and metabolic effects induced by ethanol (demonstrated by an inhibitory effect of omeprazole in both parameters) was found. These ethanol-induced effects were also inhibited by addition of Ca(2+) chelators to isolated gastric mucosa samples. Lanthanum, a Ca(2+) channel blocker, inhibited ethanol-promoted increase of oxidative metabolism. In addition, a stimulated Ca(2+) uptake by mucosal minces and increased in vivo Ca(2+) levels in cytosolic and mitochondrial fractions, were also noticed. Enhanced glucose and oxygen consumptions were associated with higher ATP and NADP+ availability, whereas cytosolic NAD/NADH ratio (assessed by mucosal levels of lactate and pyruvate) was not significantly modified by the chronic ethanol administration. In conclusion, changes in Ca(2+) homeostasis, probably mainly due to increased extracellular Ca(2+) uptake, could mediate secretory and metabolic alterations found in the gastric mucosa from rats chronically treated with ethanol.

Gastric mucosal cell proliferation in ethanol-induced chronic mucosal injury is related to oxidative stress and lipid peroxidation in rats

The oxygen free radicals-induced lipid peroxidation (LP) has been implicated in the pathogenesis of acute ethanol-induced gastric mucosal lesions. However, the role of LP in the generation of chronic gastric mucosal injury is unknown. We have developed a model of chronic mucosal injury induced by continuous ethanol ingestion for 5 days and characterized by marked alterations in plasma membranes from gastric mucosa. Therefore, LP was evaluated in this experimental model. Indicators of peroxidative activity, mucosal glutathione content, thymidine kinase activity (an index of cell proliferation), and histamine H2-receptor (H2R) binding constants were quantified in animals undergoing gastric mucosal damage. The effect of famotidine, a H2R antagonist that readily ameliorates the chronic mucosal injury, was also tested. Increased free radicals and LP levels were detected during gastritis; however, a second, higher peak of LP was noted in mucosal plasma membranes after ethanol withdrawal (recovery period). This further increase of LP coincided with active cell proliferation, decreased mucosal glutathione levels, and diminished specific cimetidine binding by H2R. Administration of famotidine accelerated the mucosal proliferative process, inducing the second lipoperoxidative episode sooner, and preserved the content of glutathione. In addition, LP correlated directly with cell proliferation and inversely with mucosal membrane cimetidine binding. In conclusion, LP seems to be involved in chronic ethanol-induced gastric mucosal injury. However, a further enhancement of plasma membrane LP occurred, associated with increased DNA synthesis and diminished cimetidine binding by membrane H2R. Therefore, increased LP could also participate in the compensatory mucosal proliferation initiated after ethanol withdrawal.

Expression of intracellular calcium channels and pumps after partial hepatectomy in rat

Ca(2+) signals regulate many cellular functions, including proliferation. They are governed by the inositol 1,4,5-trisphosphate receptor (IP(3)R), the only intracellular hepatic Ca(2+) channel and by the endoplasmic reticulum Ca(2+) pumps, SERCA. To characterise their role in regeneration, expression of their isoforms was studied after 2/3 hepatectomy by real-time quantitative PCR, Western blot and binding studies. We found an early increase in the expression of the IP(3)R isoform 1 which contrasted with the decrease of the expression of the IP(3)R isoforms 2 and 3 and of SERCA3. This results in a transient switch between IP(3)R isoforms 1 and 2, IP(3)R isoform 1 becoming predominant before the first round of mitosis. Binding studies detected a 30% diminution of the IP(3)R population at 24 h. In conclusion, the Ca(2+) signalling machinery is regulated, after hepatectomy, by changes in expression of the IP(3)R and SERCA isoforms to adapt Ca(2+) signals to the regenerative state.