Lactobacillus- and bifidobacterium-mediated antigenotoxicity in the colon of rats

Lactic acid bacteria (LAB) are proposed to have several beneficial effects, including the inactivation of carcinogens. We have studied the potential of Lactobacillus acidophilus (from a commercially available yogurt), Lactobacillus gasseri (P79), Lactobacillus confusus (DSM20196), Streptococcus thermophilus (NCIM 50083), Bifidobacterium breve and Bifidobacterium longum (from human infant stool) to prevent the induction of DNA damage by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 7.5 mg/kg body wt) in colon cells of the rat. Using the new technique of single cell microgel electrophoresis, all investigated strains were antigenotoxic toward MNNG after a single dose of 10(10) viable cells/kg body wt p.o. eight hours before the carcinogen. One-half and one-tenth of this initial dose resulted in a loss of protective activity. High doses of heat-treated L. acidophilus strains were also not antigenotoxic. One mechanism of the preventive effect could be that bacterial metabolites or components are responsible. Accordingly, selected examples were investigated in vitro in colon cells of the rat. Metabolically active L. acidophilus cells, as well as an acetone extract of the culture, prevented MNNG-induced DNA damage. Different cell fractions from L. acidophilus (cytoplasm, cell wall skeleton, cell wall) were devoid of antigenotoxic activity, whereas the peptidoglycan fraction and whole freeze-dried cells were antigenotoxic. As a second carcinogen, 1,2-dimethylhydrazine (DMH) was used. A dose- and time-response study was first performed to assess the effects of DMH in several segments of the gastrointestinal (GI) tract. Exposure for 16 hours to 15 or 25 mg DMH/kg body wt p.o. induced DNA damage in cells of the distal colon of rats, whereas no cytotoxicity was seen. Pretreatment orally with LAB on four consecutive mornings before DMH gavage (8 hours after the last LAB application) revealed that L. acidophilus, L. confusus, L. gasseri, B. longum, and B. breve inhibited the genotoxic effect of DMH. One of four S. thermophilus and one of three Lactobacillus delbrueckeii ssp. bulgaricus strains were also protective. Heat-treated L. acidophilus did not inhibit DMH-induced genotoxicity. A few aliquots of the colon cells were processed immunohistochemically for the presence of the "proliferation cell nuclear antigen" (PCNA). DMH treatment did not increase PCNA, nor was there any modulation by LAB. The effect of L. acidophilus on foreign compound-metabolizing enzymes (Phase I and Phase II) in liver and colon cells of rats revealed only one parameter to be modulated, namely, a two- to three-fold increase in the levels of NADPH-cytochrome P-450 reductase. The meaning of this finding, in terms of possible chemoprevention by LAB, remains unclear. In conclusion, our studies show that most, but not all, LAB tested could strongly inhibit genotoxicity in the GI tract of the rat and that viable LAB organisms are required for the protective effect in vivo. The comet assay technique is a powerful tool to elucidate such in vivo antigenotoxic activities in tumor target tissues.

An experimental study of spinal cord evoked potential

The characteristics of spinal cord-evoked potentials were investigated by using an in vitro spinal cord preparation. The spinal cord isolated from adult rats was immersed in a bathing chamber filled with oxygenated artificial cerebrospinal fluid (aCSF). The spinal cord-evoked potentials elicited by the stimulation of the spinal cord were recorded by using bipolar platinum electrodes. The potentials recorded consisted of early and late negative components (N1, N2). The inhibitory effect of lowered temperature on the N1 potential was clearly demonstrated. The oxygen deprivation of aCSF showed the higher sensitivity of N2 potential to hypoxia than that of N1. It was also possible to analyze the effects of potassium and magnesium ion concentration and pH on the evoked potentials. These results showed that the pure effects of various physiological and chemical factors on the spinal cord-evoked potentials can be analyzed by this experimental model.

Essential and neural transcripts from the Drosophila shaking-B locus are differentially expressed in the embryonic mesoderm and pupal nervous system

The shaking-B gene of Drosophila encodes two functions: one specifically neural and the other required for viability. Flies carrying neural mutations show a range of defects, the best characterized of which is a disruption of some synapses in the giant fibre system, while mutations in the essential function cause animals to die as first instar larvae. We have characterised an essential transcript from this locus and show that mutant lesions underlying two lethal shaking-B alleles map to its coding sequence. We also propose a new model for the topologies of Shaking-B proteins and their relatives. Essential shaking-B transcripts are found in embryonic mesodermal derivatives, while during metamorphosis both essential and neural transcripts are dynamically expressed in the pupal nervous system. Although the expression patterns of these transcripts overlap in many cells, only the neural form is expressed in the giant fibre cell bodies and the lamina and medulla of the optic lobes. This observation correlates with the phenotypes of mutations which disrupt the coding region of this neural transcript. On the basis of the expression patterns of shaking-B transcripts and the phenotypes conferred by mutations of shaking-B and homologous genes, we suggest that Shaking-B proteins and their homologues may be involved in the organisation of cellular membranes.

Sodium channel mutations in paramyotonia congenita exhibit similar biophysical phenotypes in vitro

Mutations in the skeletal muscle voltage-gated Na+ channel alpha-subunit have been found in patients with two distinct hereditary disorders of sarcolemmal excitation: hyperkalemic periodic paralysis (HYPP) and paramyotonia congenita (PC). Six of these mutations have been functionally expressed in a heterologous cell line (tsA201 cells) using the recombinant human skeletal muscle Na+ channel alpha-subunit cDNA hSkM1. PC mutants from diverse locations in this subunit (T1313M, L1433R, R1448H, R1448C, A1156T) all exhibit a similar disturbance in channel inactivation characterized by reduced macroscopic rate, accelerated recovery, and altered voltage dependence. PC mutants had no significant abnormality in activation. In contrast, one HYPP mutation studied (T704M) has a normal inactivation rate but exhibits shifts in the midpoints of steady-state activation and inactivation along the voltage axis. These findings help to explain the phenotypic differences between HYPP and PC at the molecular and biophysical level and contribute to our understanding of Na+ channel structure and function.

Voltage-dependent regulation of modal gating in the rat SkM1 sodium channel expressed in Xenopus oocytes

The TTX-sensitive rat skeletal muscle sodium channel (rSkM1) exhibits two modes of inactivation (fast vs slow) when the alpha subunit is expressed alone in Xenopus oocytes. In this study, two components are found in the voltage dependence of normalized current inactivation, one having a V1/2 in the expected voltage range (approximately -50 mV, I(N)) and the other with a more hyperpolarized V1/2 (approximately -130 mV, IH) at a holding potential of -90 mV. The I(N) component is associated with the gating mode having rapid inactivation and recovery from inactivation of the macroscopic current (N-mode), while IH corresponds to the slow inactivation and recovery mode (H-mode). These two components are interconvertible and their relative contribution to the total current varies with the holding potential: I(N) is favored by hyperpolarization. The interconversion between the two modes is voltage dependent and is well fit to a first-order two-state model with a voltage dependence of e-fold/8.6 mV and a V1/2 of -62 mV. When the rat sodium channel beta 1-subunit is coinjected with rSkM1, IH is essentially eliminated and the inactivation kinetics of macroscopic current becomes rapid. These two current components and their associated gating modes may represent two conformations of the alpha subunit, one of which can be stabilized either by hyperpolarization or by binding of the beta 1 subunit.

Metabolism of benzene and trans,trans-muconaldehyde in the isolated perfused rat liver

Perfusate from rat livers perfused with benzene (approximately 0.7-7 x 10(-4) M) or trans,trans-muconaldehyde (MUC) (10(-4) M) was extracted and analyzed by reverse-phase HPLC. Based on retention time and co-elution experiments, benzene was found to be metabolized to trans,trans-muconic acid, a urinary ring-opened metabolite of benzene and a major in vivo and in vitro metabolite of MUC. These data demonstrate that benzene ring-opening occurs in the liver. Following perfusion with MUC (a microsomal hematotoxic metabolite of benzene), trans,trans-muconic acid and three other MUC metabolites were detected in the perfusate extract, suggesting that these metabolites would be present in the circulation following metabolism of MUC.

Sodium channel mutations in paramyotonia congenita uncouple inactivation from activation

Mutations in the adult human skeletal muscle Na+ channel alpha subunit cause the disease paramyotonia congenita. Two paramyotonia congenita mutations, R1448H and R1448C, substitute histidine and cysteine for arginine in the S4 segment of domain 4. These mutations, expressed in a cell line, have only small effects on the activation of Na+ currents, but mutant channels inactivate more slowly with less voltage dependence than wild-type channels and exhibit an enhanced rate of recovery from inactivation. Increase of extracellular pH made the rate of inactivation of R1448H similar to that of R1448C, suggesting that this residue has an extracellular location and that its charge is important for normal inactivation. Analysis of single-channel data reveals that mutant channels inactivate normally from closed states, but poorly from the open state. The data suggest a critical role for the S4 helix of domain 4 in coupling between activation and inactivation.

Modulation of voltage-dependent sodium and potassium currents by charged amphiphiles in cardiac ventricular myocytes. Effects via modification of surface potential

Modulation of voltage-dependent sodium and potassium currents by charged amphiphiles was investigated in cardiac ventricular myocytes using the patch-clamp technique. Negatively charged sodium dodecylsulfate (SDS) increased amplitude of INa, whereas positively charged dodecyltrimethylammonium (DDTMA) decreased INa. Furthermore, SDS shifted the steady-state activation and inactivation of INa in the negative direction, whereas DDTMA shifted the curves in the opposite direction. These shifts provided an explanation for the changes in current amplitude. Activation and inactivation kinetics of INa were accelerated by SDS but slowed by DDTMA. These changes in both steady-state gating and kinetics of INa are consistent with a decrease of the intramembrane field by SDS and an increase of the field by DDTMA due to an alteration of surface potential after their insertion into the outer monolayer of the sarcolemma. The effect of SDS on the steady-state inactivation of INa was concentration dependent and partially reversed by screening surface charges with increased extracellular [Ca2+]. These amphiphiles also altered the activation of the delayed rectifier K+ current (IK,del), producing a shift in the negative direction by SDS but in the positive direction by DDTMA. These results suggest that the insertion of charged amphiphiles into the cell membrane alters the behavior of voltage-dependent INa and IK,del by changing the surface charge density, and consequently the surface potential and implies, although indirectly, that the lipid surface charges are important to the voltage-dependent gating of these channels.

Effects of charged amphiphiles on cardiac cell contractility are mediated via effects on Ca2+ current

Exposure of isolated adult rabbit myocytes to the negatively charged amphiphile dodecylsulfate (DDS; 10 microM) increased the contraction amplitude to 185% of control. The positively charged amphiphile dodecyltrimethylammonium (DDTMA; 10 microM) decreased the amplitude to 58%. DDS increased Ca2+ uptake by the same cells, but this uptake was partially prevented by nifedipine. DDTMA had no effect on Ca2+ uptake. Ca2+ binding to isolated sarcolemma of neonatal heart cells was increased by 10 microM DDS and, at higher concentrations, reduced by DDTMA. Single-cell voltage-clamp studies, using isolated rabbit myocytes, showed that DDS enhanced L-type Ca2+ currents (ICa,L), whereas DDTMA depressed ICa,L. DDS shifted current-voltage (I-V) and isochronal inactivation curves of ICa,L in the negative direction, whereas DDTMA shifted them in positive direction. Furthermore, DDS depressed T-type Ca2+ currents (ICa,T), and DDTMA enhanced ICa,T. The inotropic effects of the amphiphiles are therefore mediated to a significant degree by ICa,L. The shifts in the I-V and inactivation curves of ICa,L and the effect on ICa,T can be explained by changes in the actual membrane potential (Em), induced by the insertion of the amphiphiles in the outer monolayer of the sarcolemma. However, the changes in the Em do not explain the effect on the maximal current, indicating effects on the channel per se, possibly by an alteration of the lipid environment.

Contractile shortening response of ventricular cells to extracellular acidosis. Evidence for two-site control of H+-Ca2+ interaction

The effect of extracellular acidosis on contraction of single isolated ventricular cells from rabbit was measured in a system in which pHo could be changed in less than 200 msec. The contractile response to acidotic levels was complete within 25 seconds. The response was measured 30 seconds after pHo was decreased to 7.0, 6.5, 6.0, and 5.5 at each of 8 [Ca]o levels (0.125-4.0 mM). Cell shortening versus [Ca]o was plotted to construct a curve for each pHo level, with each point relative to shortening at pH 7.5, [Ca]o = 1 mM (100% value). Calcium current (1 mM [Ca]o) was also measured 30 seconds after pHo was decreased from 7.5 to 6.5 with single-cell patch clamp technique. The contractile response to extracellular acidosis is accurately predicted by assuming two (probably sarcolemmal) sites at which H+ ions affect calcium binding and/or flux: (equation; see text) The first factor represents a set of sites that are proposed to control access, dependent on the degree of their ionization, to sites represented by the second factor. The latter sites are proposed to accept calcium according to mass-action law. The response of calcium channel current to extracellular acidosis was also complete and reversible within 25 seconds. The current response indicates that the two-site model could be predictive for the effect of extracellular acidosis on calcium current in ventricular cells.

Effects of exogenous free radicals on electromechanical function and metabolism in isolated rabbit and guinea pig ventricle. Implications for ischemia and reperfusion injury

Oxygen-derived free radicals have been implicated in the pathogenesis of cardiac dysfunction during ischemia, postischemic myocardial "stunning," and reperfusion injury. We investigated the effects of oxygen-derived free radicals on cardiac function in intact isolated rabbit hearts and single guinea pig ventricular myocytes. In the intact rabbit ventricle, exposure to free radical-generating systems caused increased cellular K+ efflux, shortening of the action potential duration, changes in tension, and depletion of high energy phosphates similar to ischemia and metabolic inhibition. In patch-clamped single ventricular myocytes, free radical-generating systems activated ATP-sensitive K+ channels, decreased the calcium current, and caused cell shortening by irreversibly inhibiting glycolytic and oxidative metabolism. The results suggest that free radicals generated during ischemia and reperfusion may contribute to electrophysiologic abnormalities and contractile dysfunction by inhibiting glycolysis and oxidative phosphorylation. Inhibition of metabolism by free radicals may be an important factor limiting functional recovery from an ischemic insult after reestablishment of effective blood flow.

A general theory of chemical cytotoxicity based on a molecular model of the living cell, the Bhopalator

To define the molecular processes underlying toxicological manifestations experimentally measured on the cellular level, it is essential to have available a molecular model of the living cell itself. The Bhopalator is a molecular model of the living cell formulated by integrating the three major branches of biology within a coherent theoretical framework - the Watson-Crick molecular genetics, the conformon theory of enzymic catalysis, and the theory of dissipative structures developed by I. Prigogine. According to this model, the living cell is a self-moving, self-thinking and self-reproducing machine (automaton) that receives information and energy from its environment, processes them according to the genetic programs stored in DNA, and generates output signals to environment in order to realize teleonomically designed functions. The Bhopalator suggests a set of general statements useful in toxicological research, and these statements have been utilized to provide possible answers to several fundamental questions raised by recent experimental findings on chemically-induced cell injury and death.

Inhibition of para-nitrophenol extraction by stimulation of the hepatic nerves in the perfused rat liver

The influence of perivascular stimulation of the hepatic nerves on the extraction of para-nitrophenol (pNP) was studied in rat liver perfused in situ without recirculation. Electrical stimulation of the hepatic nerve plexus, which leads to a predominant activation of the sympathetic nerves, caused a decrease in pNP extraction, an increase in glucose output and a reduction in perfusion flow. Sodium nitroprusside (NPN) an inhibitor of vascular smooth muscle contraction, prevented the hemodynamic alterations without affecting the metabolic changes. These results suggest that sympathetic liver nerves regulate conjugation of pNP directly rather than indirectly via hemodynamic alterations.

Potential role of activated macrophages in acetaminophen hepatotoxicity. II. Mechanism of macrophage accumulation and activation

Treatment of rats with acetaminophen (1.2 g/kg) results in the accumulation of activated macrophages in the centrilobular regions of the liver. To study the mechanism by which these cells accumulate and become activated, we examined the release of chemotactic and activating factors from cultured hepatocytes treated with acetaminophen (10-100 microM). We found a dose- and time-related generation of Kupffer cell and monocyte chemotactic activity by acetaminophen-treated hepatocytes. The maximum response was observed with a 25% dilution of medium collected 24 hr following treatment of hepatocytes with acetaminophen. Using a checkerboard assay, the factor in conditioned medium was determined to induce chemotaxis as well as chemokinesis in both Kupffer cells and monocytes. The hepatocyte-derived chemotactic factor was also found to be stable to freeze-thawing but to lose activity following heat or trypsin treatment. These results, together with our findings that chemotactic activity was eluted in the void volume following Sephadex G-25 size exclusion chromatography, suggested that the chemotactic factor released by hepatocytes is a large molecular weight protein. The release of Kupffer cell activating factors by acetaminophen-treated hepatocytes was also examined. Hepatocyte-conditioned medium was found to stimulate Kupffer cell phagocytosis and superoxide anion release, two characteristics of activated macrophages. These effects were maximal with conditioned medium collected from hepatocytes 24 hr following treatment with 50-100 microM acetaminophen. Acetaminophen alone had no effect on chemotaxis, phagocytosis, or superoxide anion production by Kupffer cells or monocytes. Taken together, these results suggest that macrophage accumulation and activation in the liver following acetaminophen treatment may be mediated, at least in part, by factors released from hepatocytes.

The bhopalator: a molecular model of the living cell based on the concepts of conformons and dissipative structures

A molecular model of the living cell has been formulated based on a new theory of enzymic catalysis which takes into account the complementary roles of free energy and genetic information. The elementary units of free energy and genetic information that are necessary and sufficient for effectuating molecular mechanisms responsible for the life of the cell are called conformons. Conformons are visualized as a collection of a small number of catalytic residues of enzymes or segments of nucleic acids that are arranged in space and time with appropriate force vectors so as to cause chemical transformations or physical changes of a substrate or a bound ligand. So defined, conformons provide a plausible molecular means to link the genetic information stored in DNA and its ultimate expression, namely networks of coupled intracellular biochemical reactions and physical processes maintained by a continuous dissipation of free energy--dissipative structures of Prigogine. The proposed model of the living cell appears to possess the potential for bridging the gap between molecular biology and the biology of multicellular systems.

Control of oxygen uptake, microcirculation and glucose release by circulating noradrenaline in perfused rat liver

The effect of noradrenaline on oxygen uptake, on periportal and perivenous oxygen tension at surface acini, on microcirculation and on glucose output were studied in isolated rat livers perfused at constant flow with Krebs-Henseleit-hydrogen carbonate buffer containing 5mM glucose and 2mM lactate. Noradrenaline at 1 microM concentration caused a decrease in oxygen uptake, while at 0.1 microM it led to an increase. Both high and low doses of noradrenaline decreased the tissue surface oxygen tension in periportal and - after a transient rise - in perivenous areas. Noradrenaline at an overall constant flow caused an increase of portal pressure and an alteration of the intrahepatic distribution of the perfusate: at the surface of the liver and in cross sections infused trypan blue led to only a slightly heterogeneous staining after a low dose of noradrenaline but to a clearly heterogeneous staining after a high dose. Both high and low doses of noradrenaline stimulated glucose release. All effects could be inhibited by the alpha-blocking agent phentolamine. In conclusion, control of hepatic oxygen consumption by circulating noradrenaline is a complex result of opposing hemodynamic and metabolic components: the microcirculatory changes inhibit oxygen uptake; they dominate after high catecholamine doses. The metabolic effects include a stimulation of oxygen utilization; they prevail at low catecholamine levels. The noradrenergic control of glucose release is also very complex, involving direct, metabolic and indirect, hemodynamic components.

Is hypoxia involved in the mechanism of alcohol-induced liver injury?

Since alcoholism is a major health problem, mechanisms responsible for various forms of alcoholic liver disease (e.g., fatty liver, alcoholic hepatitis, and cirrhosis) require elucidation. Knowledge of these mechanisms is needed to provide a sound framework to treat alcoholic liver disease, to prevent its occurrence and to identify those most susceptible to it. Israel and co-workers proposed that ethanol-induced necrosis results from hypoxia to centrilobular hepatocytes as a consequence of an alcohol-induced increase in hepatic oxygen utilization (Y. Israel, H. Kalant , H. Orrego , J. M. Khanna , L. Videla , and J. M. Phillips, 1975, Proc. Natl. Acad. Sci. USA, 72(3), 1137-1141). We have employed several new techniques to evaluate this hypothesis. Procedures have been developed to make measurements of hepatic metabolism within the hepatic lobule in the isolated, perfused liver using miniature light guides and oxygen electrodes. By comparing these lobular measurements to global metabolism and to hepatic morphology determined by light and electron microscopy, a coherent, quantitative description of lobular oxygen metabolism is emerging. With these techniques, the lobular oxygen gradient was measured directly in isolated, perfused rat livers. This gradient was elevated in livers from ethanol-treated rats, an effect which was blocked by the antithyroid drug, propylthiouracil. Restriction of oxygen delivery to the isolated liver produced stable, circumscribed zones of virtual anoxia localized around the central vein. Anoxic stress led within minutes to centrilobular injury with complete sparing of periportal areas. Cellular injury was characterized by the formation of membranous blebs on the surface of centrilobular hepatocytes. When hypoxic tissue was reoxygenated , blebs were released into the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of oxygen consumption and microcirculation by alpha-sympathetic nerves in isolated perfused rat liver

In isolated rat liver perfused at constant flow with erythrocyte-free Krebs-Henseleit bicarbonate buffer containing 5 mM glucose and 2 mM lactate, perivascular stimulation of the hepatic nerves caused a rapid decrease of oxygen uptake, a decrease of the periportal and, after a transient rise, of the perivenous tissue po2 of surface acini, an increase of portal pressure, and an enhancement of glucose output. Furthermore, nerve stimulation changed the intrahepatic distribution of the perfusate drastically. Infusion of trypan blue 20 s after nerve stimulation resulted in a heterogeneous staining of the liver both at the surface and in cross-sections, while it led to a homogeneous distribution in non-stimulated controls. It is concluded that the major component in the mechanism of the nerve-dependent decrease of oxygen uptake is the microcirculatory change rather than a metabolic effect.

Stimulation of mixed-function oxidation of 7-ethoxycoumarin in periportal and pericentral regions of the perfused rat liver by xylitol

Rates of O-deethylation of 7-ethoxycoumarin by perfused livers from fasted, phenobarbital-treated rats were 3.7 mumol X g-1 X h-1. Approximately 50% of the product was conjugated. When rates of 7-ethoxycoumarin O-deethylation were varied by infusing different concentrations of substrate, a good correlation (r = 0.91) was found between rates of O-deethylation of 7-ethoxycoumarin and fluorescence of 7-hydroxycoumarin detected from the liver surface. Micro-light guides (tip diameter 170 microns) placed on periportal and pericentral regions on the liver surface were used to monitor the conversion of nonfluorescent 7-ethoxycoumarin to fluorescent 7-hydroxycoumarin. The O-deethylation of 7-ethoxycoumarin to 7-hydroxycoumarin increased fluorescence 64% and 28% in pericentral and periportal regions of the liver lobule, respectively. Rates of 7-ethoxycoumarin O-deethylation estimated from these increases in fluorescence were 5.2 mumol X g-1 X h-1 in pericentral and 2.2 mumol X g-1 X h-1 in periportal regions of the liver. During mixed-function oxidation of 7-ethoxycoumarin, the oxidation:reduction state of NADP(H) was similar in both regions of the liver lobule. Xylitol (2 mM) decreased the NADP+/NADPH ratio and stimulated rates of drug metabolism in both regions of the liver lobule. This indicates that conditions exist where the supply of NADPH is an important rate-determining factor for 7-ethoxycoumarin metabolism in both periportal and pericentral regions of the liver lobule.

Cell surface changes and enzyme release during hypoxia and reoxygenation in the isolated, perfused rat liver

We examined the effects of hypoxia and reoxygenation in isolated, perfused rat livers. Hypoxia induced by a low rate of perfusion led to near anoxia confined to centrilobular regions of the liver lobule. Periportal regions remained normoxic. Within 15 min, anoxic centrilobular hepatocytes developed surface blebs that projected into sinusoids through endothelial fenestrations. Periportal hepatocytes were unaffected. Both scanning and transmission electron microscopy suggested that blebs developed by transformation of preexisting microvilli. Upon reoxygenation by restoration of a high rate of perfusion, blebs disappeared. Other changes included marked shrinkage of hepatocytes, enlargement of sinusoids, and dilation of sinusoidal fenestrations. There was also an abrupt increase in the release of lactate dehydrogenase and protein after reoxygenation, and cytoplasmic fragments corresponding in size and shape to blebs were recovered by filtration of the effluent perfusate. We also studied phalloidin and cytochalasin D, agents that disrupt the cytoskeleton. Both substances at micromolar concentrations caused rapid and profound alterations of cell surface topography. We conclude that hepatic tissue is quite vulnerable to hypoxic injury. The morphological expression of hypoxic injury seems mediated by changes in the cortical cytoskeleton. Reoxygenation causes disappearance of blebs and paradoxically causes disruption of cellular volume control and release of blebs as cytoplasmic fragments. Such cytoplasmic shedding provides a mechanism for selective release of hepatic enzymes by injured liver tissue.

Effect of size on portal circulation of hepatic nodules from carcinogen-treated rats

The portal circulation of diethylnitrosamine-initiated nodules (0.5 to 7 mm in diameter) was studied in rat livers perfused exclusively via the portal vein. Microlight guides were placed on normal and nodular tissue on the capsular surface of the liver to measure pyridine nucleotide fluorescence (366 leads to 450 nm). When oxygen tension of the inflow perfusate was lowered, fluorescence in both normal tissue and small nodules (less than 2 mm in diameter) increased sharply due to the reduction of pyridine nucleotides, indicating previous normoxia. In contrast, similar manipulations did not increase fluorescence in nodules greater than 2 mm in diameter, demonstrating that nicotinamide adenine dinucleotide was reduced maximally previously; i.e., the nodules were anoxic. Direct measurements of nodule oxygen concentrations with a miniature oxygen electrode confirmed these results. 7-Hydroxycoumarin or fluorescein could be detected with micro-light guides in normal tissue and nodules less than 2 mm in diameter but not in nodules greater than 2 mm in diameter. Furthermore, fluorescent microscopy indicated an absence of fluorescein in nodules greater than 2 mm in diameter. Therefore, with four independent optical and polarographic techniques, we have demonstrated reduced portal circulation in nodules greater than 2 mm in diameter; however, smaller nodules could not be differentiated from normal tissue.

Aldehyde dehydrogenase-dependent acetaldehyde metabolism in periportal and pericentral regions of the perfused rat liver

NADH fluorescence (366 leads to 450 nm) was measured with a large tipped light guide from the surface of rat liver perfused with hemoglobin-free medium without recirculation. A good correlation (r = 0.93) was found between the increase in NADH fluorescence and the rate of oxidation of infused acetaldehyde (0.1-4.0 mM). By using microlight guides placed on either periportal or pericentral areas of the liver, it was found that infusion of acetaldehyde increased NADH fluorescence first in periportal regions and then in pericentral areas. During retrograde perfusions, NADH fluorescence in pericentral areas increased before portal areas. By using the correlation between the increase in NADH fluorescence and the rate of acetaldehyde uptake established with the large light guide, rates of acetaldehyde uptake in pericentral and periportal areas were estimated from the microlight guide measurement of the periportal and pericentral NADH fluorescence increments caused by acetaldehyde infusions. Half-maximal acetaldehyde uptake was observed at about 0.8 mM in both regions. Maximal rates of acetaldehyde uptake were 212 and 197 mumol/g/hr in periportal and pericentral regions, respectively. The results indicate that rates of aldehyde dehydrogenase-dependent acetaldehyde oxidation are similar in periportal and pericentral regions of the liver lobule.

Selective increase in pericentral oxygen gradient in perfused rat liver following ethanol treatment

The oxygen gradient across the liver lobule was measured in isolated, hemoglobin-free perfused livers from control and ethanol-treated rats using micro-light guides and miniature oxygen electrodes. Both techniques yielded similar values for the lobular, periportal and pericentral oxygen gradients. Oxygen uptake increased 33% in livers from rats treated with ethanol for 4 to 6 weeks. In addition, the pericentral oxygen gradient increased by 100%, but the periportal gradient was unchanged. These observations suggest that chronic ethanol treatment may increase the rate of cellular respiration in pericentral regions of the liver lobule selectively. One possible explanation for a region-specific effect of ethanol may be ethanol-induced inhibition of glycolysis which predominates in pericentral hepatocytes.

Hypoxic hepatocellular injury

Low flow hypoxia to the isolated, perfused rat liver produced stable, circumscribed zones of virtual anoxia which were confined to centrilobular regions of the liver lobule. As a result, centrilobular hepatocytes were injured while periportal tissue was spared. In hypoxic areas, blebs of hepatocyte plasma membrane cytoplasm protruded into sinusoids through fenestrations of the endothelium, evidently as a result of disruption of the cytoskeleton. Upon resumption of normal flow rates (reoxygenation), blebs disappeared and hepatocytes decreased markedly in volume. Concomitantly, sinusoids widened, endothelial fenestrations dilated, and lactate dehydrogenase activity appeared in the effluent. Filtration of perfusates following resumption of flow yielded cytoplasmic fragments, and it was concluded that blebs were released into the circulation. This shedding of cytoplasmic fragments may represent the cellular basis for the appearance of hepatic enzymes in the sera of patients with liver disease.

Metabolic heterogeneity in the perfused rat liver

New methods have been developed to monitor metabolic events non-invasively within periportal and pericentral regions of perfused rat livers. These techniques utilize two-fiber micro-light guides and miniature oxygen electrodes positioned on identified lobular regions of the perfused liver based on differential pigmentation of periportal and pericentral areas. Two-fiber micro-light guides detect the fluorescence of native and introduced fluors and are used to monitor redox changes of endogenous pyridine nucleotides and the generation of fluorescent products (e.g., 7-hydroxycoumarin) from exogenous substrates. Changes in fluorescence detected with two-fiber micro-light guides are correlated with changes measured with large, multi-fiber light guides and with whole organ rates of metabolism. Subsequently, local rates are estimated. With these techniques, we show that (a) rates of ethanol and acetaldehyde metabolism are similar in periportal and pericentral regions of the liver lobule; (b) mixed-function oxidation predominantes in pericentral regions in livers from phenobarbital-treated rats; (c) rates of sulfation of 7-hydroxycoumarin are greater in periportal than in pericentral hepatocytes; and (d) oxygen uptake is approximately 3-fold greater in periportal than in pericentral areas of the liver lobule.

Periportal and pericentral pyridine nucleotide fluorescence from the surface of the perfused liver: evaluation of the hypothesis that chronic treatment with ethanol produces pericentral hypoxia

Pyridine nucleotide fluorescence made from the surface of the hemoglobin-free perfused rat liver was measured continuously by using a "micro-light guide" placed on selected periportal and pericentral regions of the liver lobule. From the portal oxygen tension at which pyridine nucleotide reduction first occurred in pericentral regions, the oxygen gradient across the liver lobule was estimated in livers from rats treated chronically with ethanol or sucrose. Chronic treatment with ethanol increased the average lobular oxygen gradient from 275 to 400 torr (1 torr = 133 Pa), primarily due to the increase in the oxygen gradient in pericentral regions. Ethanol treatment also increased hepatic oxygen uptake significantly, from 110 to 144 (mumol/g)/hr. Treatment with the antithyroid drug 6-propyl-2-thiouracil reversed the effect of ethanol on O2 uptake and on the lobular oxygen gradient. The oxygen gradients measured with the micro-light guide were confirmed by direct measurement of tissue oxygen tensions in periportal and pericentral areas by using an oxygen electrode. These data are consistent with the hypothesis that chronic treatment with ethanol causes the pericentral region of the liver lobule to become susceptible to hypoxic cellular injury. This may be responsible, at least in part, for the localized hepatotoxic effects of ethanol.

Rates of alcohol dehydrogenase-dependent ethanol metabolism in periportal and pericentral regions of the perfused rat liver

Infusion of ethanol into hemoglobin-free perfused rat liver caused an increase in NADH fluorescence (366 leads to 450 nm) which was measured with a large-tip (2-mm) light guide placed on the surface of the liver. A linear correlation (r = 0.83) was observed between the increase in NADH fluorescence and rate of ethanol uptake in the concentration range 0.05--2.0 mM. When a micro-light guide (tip diameter 170 micrometer) was placed on periportal or pericentral regions of the liver surface, the maximal fluorescence increase due to ethanol (2 mM) was 31.2 +/- 2.0 and 31.9 +/- 1.7% in periportal and pericentral regions, respectively. The infusion of 4-methylpyrazole (80 microM), an inhibitor of alcohol dehydrogenase, completely abolished the fluorescence increase in both regions, indicating that the changes are entirely attributable to perturbation of cofactor levels due to alcohol dehydrogenase-dependent ethanol metabolism. Using the correlation between the NADH fluorescence increase and rate of ethanol uptake, rates of ethanol metabolism in periportal and pericentral regions were calculated. Values for maximal ethanol uptake were identical in periportal and pericentral regions. Half-maximal ethanol uptake was observed at 0.24 and 0.25 mM ethanol in periportal and pericentral regions, respectively. These results indicate that the rates of alcohol dehydrogenase-dependent ethanol metabolism are similar in periportal and pericentral regions of the liver lobule.

Centrilobular injury following hypoxia in isolated, perfused rat liver

Hypoxia was produced in isolated, hemoglobin-free, perfused rat liver by reducing the flow rate of oxygen-carrying fluid entering the organ. The procedure caused anoxia in centrilobular regions. In these anoxic areas, structural derangements developed rapidly, characterized by bleb-like protrusions of hepatocyte plasma membrane through fenestrations in the sinusoidal endothelium. Periportal tissue remained normoxic and was completely spared. Cellular injury resulting from localized anoxia may play an important role in the pathogenesis of centrilobular liver disease.

Centrilobular injury following hypoxia in isolated, perfused rat liver

Hypoxia was produced in isolated, hemoglobin-free, perfused rat liver by reducing the flow rate of oxygen-carrying fluid entering the organ. The procedure caused anoxia in centrilobular regions. In these anoxic areas, structural derangements developed rapidly, characterized by bleb-like protrusions of hepatocyte plasma membrane through fenestrations in the sinusoidal endothelium. Periportal tissue remained normoxic and was completely spared. Cellular injury resulting from localized anoxia may play an important role in the pathogenesis of centrilobular liver disease.

Ethanol-induced changes in the intralobular oxygen gradient of perfused rat liver

A new tissue fluorometric method was developed to estimate the intralobular oxygen gradient in hemoglobin-free perfused rat liver. The method employs a two-branch micro-light guide with a tip diameter of 170 mu. With this light guide, it was possible to measure pyridine nucleotide fluorescence (366 nm leads to 450 nm) from periportal and pericentral regions of the liver lobule. By measuring inflow PO2 values at which pyridine nucleotide fluorescence increased in the pericentral regions of the liver lobule, the mean intralobular oxygen gradient was estimated. The measured gradient was approximately 180 torr in livers from sucrose-treated control rats. Chronic treatment with ethanol increased both the mean intralobular oxygen gradient and the rate of hepatic oxygen uptake by 30%. The antithyroid drug, 6-propyl-2-thiouracil, completely reversed the effects of ethanol on both the intralobular oxygen gradient and the rate of oxygen uptake. These data present direct physical evidence that the increased tissue respiration induced by chronic ethanol treatment indeed accentuates the intralobular oxygen gradient and thus support the hypothesis that selective depletion of oxygen in the pericentral region of the liver lobule may underlie ethanol-induced cellular injury confined to this site.

Micro-light guides: a new method for measuring tissue fluorescence and reflectance

Three-way light guides containing one or more strands of 25-micron or 80-micron diameter optical fibers in each channel have been constructed and used to measure the NADH fluorescence and UV reflectance from mitochondrial suspensions, the perfused, hemoglobin-free rat liver, and the perfused beating interventricular septum of the rabbit. The optical changes measured with these so-called micro-light guides, which have channels containing one or several strands of optical fibers less than 100 micron, are comparable in magnitude with those measured using much larger conventional light guides. The effect of light scattering on the fluorescence channel has been determined and an empirical equation for correcting the fluorescence channel for light scattering has been obtained for mitochondrial suspensions. A mathematical equation characterizing the optical behavior of a two-way micro-light guide has been derived and has been shown to account satisfactorily for reflectance and fluorescence measurements of a mat surface in air.

Action of norepinephrine on microcirculation and PO2 distribution in the isolated perfused rat liver

The addition of a potent vasoconstrictor, such as norepinephrine, induces an influx of sodium and an efflux of calcium and potassium in the parenchymal cells of the perfused liver. This reaction can be reversed by the addition of dihydroergotoxine mesylate (active substance of Hydergine). The example shows clearly that very distinct biological signals are generated under such conditions at the membrane level of the hepatocytes and presumably of other cells of liver tissue. At present, our investigations cannot clearly answer the question of whether or not swelling the shrinkage of parenchymal cells and of endothelial cells can serve as an additional mechanism for regulating microcirculation.

Disturbances of extracellular pK, pNa and pH during no-flow anoxia

The initial period of no-flow anoxia can be divided in at least two parts. During the first period lasting approximately 1 min., the O2 available in tissue gives rise to CO2 which increases hydrogen ion activity and may lead to Na+ influx2 (presumably due to increased membrane permeability to Na+). In the second period, starting after the first minute, the increase in lactate content leads to further decrease in pH and is accompanied by extensive sodium influx and a distinct potassium efflux. However, it is striking that the isolated perfused rat liver is able to tolerate 1 hour of norm-flow anoxia without severe cellular damage, whereas two minutes of no-flow anoxia lead to a decrease in cellular ATP content by 28%.

Two-dimensional analysis of the redox state of the rat cerebral cortex in vivo by NADH fluorescence photography

A photographic method for measuring two-dimensional changes in NADH fluorescence and hemoglobin distributions in the rat cerebral cortex in vivo has been developed. Intracellular NADH was excited by UV light peaking at 360 nm and the emission was observed through a window with the maximum transmission at 450 nm. The fluorescence photographs (360 leads to 450 nm) required 20-25 sec exposures at the aperture opening of f/5.6 and the reflectance photographs (360 leads to 360 nm) 10 sec exposures at f/32. The digitization of photographic images was achieved either by a PDP-8-controlled microdensitometer coupled to an A/D converter or by a combination of a manually operated microdensitometer and a computer-controlled digitizer. In the latter case, a photographic negative was scanned with a Joyce-Loebl microdensitometer in parallel lines 170 mum apart, and the densitometric tracings were digitized with a PDP-8-controlled TV digitizer. The digital data were processed by DEC PDP-10 computer and the results were displayed in 3-dimensional surfaces. Nitrogen anoxia caused increases in fluorescence at 450 nm ranging from 10 to 75% fo the normoxic fluorescence intensities (after correcting for the logarithmic characteristics of the photographic films) and decreases in reflectance intensities in the range of 10-30%. The spatial resolution of the present technique is limited to approximately 30 mum X 30 mum on the cortical surface and the time resolution to 10-25 sec. The optical properties of the cerebral cortex in vivo appear to be controlled primarily by blood vessel patterns and hemodynamic factors and secondarily by the redox state of the tissue. Evidence for a heterogeneous redox response of the cerebral cortex toward N2 anoxia was obtained.

Transductional and structural principles of the mitochondrial transducing unit

The electromechanochemical model has been reformulated to take account of the close connection between energy coupling and catalysis. In catalysis the protein is programmed to utilize thermal energy to produce local strains in the catalytic cavity and to generate conformational states that favor substrate --> product conversion. Energy coupling involves transfer of vibrational energy through the protein. Underlying these two energy transductional maneuvers is the concept of a pulsating protein capable of redistributing electromechanochemical potential energy in a programmed fashion. The mitochondrial supermolecule has been defined, and it has been shown how the supermolecule concept rationalizes the coupling options, the stoichiometry of the coupling complexes, and the multistep character of electron transfer.