Sucrose Space Research Articles

Effect of spherical and cubical space holders on the microstructural characteristics and its consequences on mechanical and thermal properties of open-cell aluminum foam

The effect of relative density (RD) and shape of the space holder on microstructural characteristics and compressive behavior of open-cell aluminum foams (OAFs) have been studied. OAFs with tailored porous morphologies (50–81%) were successfully prepared through space holder technique using spherical shape carbamide and cubic shape sucrose space holders in various amounts. Al powder and space holders were mixed with 2 wt% of polyvinyl alcohol (PVA) binder solution, compacted at 300 MPa and finally sintered at 650 °C for 3 h. It was observed that the microstructural characteristics of OAFs varied in accordance with the shapes of space holders. The results reveal that the OAFs prepared with carbamide show smooth microstructure, higher plateau stress (~3 times), higher energy absorption (~3 times) and higher Young's modulus, but lower densification strain, compared to the OAFs prepared with sucrose. The Young's modulus, plateau stress, and energy absorption of OAFs, follow the power-law relationship as a function of its RD irrespective of the shape of space holders. The thermal conductivity of Al-carb and Al-suc OAFs are noted to be not much in variation irrespective of the shape of the pores.

Nitric oxide induced sinusoidal relaxation after a propranolol priming dose in the perfused rat liver reduces propranolol availability on subsequent dosing

1. The present study sought to explain the mechanism leading to reduced availability of propranolol when given after a priming dose in the single-pass perfused rat liver. 2. Extracellular sucrose space (as a measure of sinusoidal relaxation) in perfused rat liver before and after propranolol or propranolol and N(G)-nitro-L-arginine methyl ester (L-NAME; nitric oxide (NO) synthase inhibitor) treatment were examined. The results showed that propranolol induces sinusoidal relaxation in the perfused liver and this effect could be abolished by NO synthase inhibitor L-NAME. 3. Two bolus injections of propranolol were given to the isolated perfused rat liver and outflow concentration-time profiles of intact propranolol were determined. A two-phase physiologically based organ pharmacokinetic model was applied to estimate hepatocellular influx, efflux, binding, ion-trapping and metabolic elimination pharmacokinetic parameters for propranolol. The recovery of propranolol in the second injection was approximately 54% of that in the first injection. The permeability-surface area product, the binding and the intrinsic clearance all increased significantly after prior exposure of the rat liver to the first bolus of propranolol (P < 0.05). 4. Based on the findings of the present study, we propose that the most likely explanation for the reduced availability of a second propranolol dose (after administration of a priming dose) in the perfused liver is a consequence of the NO-mediated sinusoidal relaxation effect of propranolol, arising from the priming dose. This observation supports the view that the pharmacokinetics of some drugs might be altered by the pharmacodynamic effects of the same drug given earlier in the perfused liver.

Distribution of Gefitinib to the Brain Is Limited by P-glycoprotein (ABCB1) and Breast Cancer Resistance Protein (ABCG2)-Mediated Active Efflux

Gefitinib is an orally active inhibitor of the epidermal growth factor receptor approved for use in patients with locally advanced or metastatic non-small cell lung cancer. It has also been evaluated in several clinical trials for treatment of brain tumors such as high-grade glioma. In this study, we investigated the influence of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) on distribution of gefitinib to the central nervous system. In vitro studies conducted in Madin-Darby canine kidney II cells indicate that both P-gp and BCRP effectively transport gefitinib, limiting its intracellular accumulation. In vivo studies demonstrated that transport of gefitinib across the blood-brain barrier (BBB) is significantly limited. Steady-state brain-to-plasma (B/P) concentration ratios were 70-fold higher in the Mdr1a/b(-/-) Bcrp1(-/-) mice (ratio of approximately 7) compared with wild-type mice (ratio of approximately 0.1). The B/P ratio after oral administration increased significantly when gefitinib was coadministered with the dual P-gp and BCRP inhibitor elacridar. We investigated the integrity of tight junctions in the Mdr1a/b(-/-) Bcrp1(-/-) mice and found no difference in the brain inulin and sucrose space between the wild-type and Mdr1a/b(-/-) Bcrp1(-/-) mice. This suggested that the dramatic enhancement in the brain distribution of gefitinib is not due to a leakier BBB in these mice. These results show that brain distribution of gefitinib is restricted due to active efflux by P-gp and BCRP. This finding is of clinical significance for therapy in brain tumors such as glioma, where concurrent administration of a dual inhibitor such as elacridar can increase delivery and thus enhance efficacy of gefitinib.

Quantitative evaluation of the effect of propylene glycol on BBB permeability

To establish the blood-brain barrier (BBB) blocking property of propylene glycol (PG) using the (14)C sucrose technique, quantitatively evaluate the effect of PG on BBB permeability using an MRI technique based on graphical analysis, and demonstrate the sensitivity of MRI for testing newer investigational drugs. Brain uptake of sucrose was measured in treated (PG+) and untreated (PG-) rats using a (14)C sucrose technique in rat brains (N = 10) that had undergone two hours of middle cerebral artery occlusion (MCAO) and three hours of reperfusion. Another group of PG+ and PG- rats (N = 8) underwent MRI. T2-weighted (T2W) and diffusion-weighted (DW) images were acquired on a 4.7T MR system. A rapid T1 mapping protocol was implemented to acquire a baseline data set followed by postinjection data sets at regular intervals. The data were postprocessed pixelwise to generate permeability coefficient color maps. A significant (P < 0.05) reduction in (14)C sucrose space was observed on the ischemic side of PG+ rats only. Permeability coefficient estimates obtained by MRI from the ipsilateral hemisphere in PG+ rats were significantly lower than those in PG- rats (P < 0.05). There was no significant change on the contralateral side in PG+ rats. The results show that PG protects the BBB in ischemic stroke, and MRI measurements are sufficiently sensitive to noninvasively detect small drug effects. MRI is useful for evaluating the BBB blocking effect of PG in an ischemic stroke model of rat brain. The results from the MR experiment agree well with findings from the (14)C sucrose technique.

The hemodynamic effects of zymosan in the perfused rat liver

The actions of zymosan on hepatic microcirculation and on the cell membrane permeability were investigated using the multiple-indicator dilution technique. The experimental system was the perfused rat liver. [ 3H]Water, [ 3H]sucrose and [ 14C]urea or [ 14C]bicarbonate were simultaneously injected into the portal vein. Mean transit times, distribution spaces, variances, linear superpositions and transfer coefficients across the plasma membrane were calculated. Zymosan had no net effect on the great vessels space but increased the extracellular sucrose space and decreased the aqueous cell space. Zymosan impaired the flow-limited distribution and increased the normalized variances of all tracers. The increase in the portal pressure caused by zymosan results most probably from a constriction just after or at the exit of the sinusoids. Impairment of the flow-limited distribution of tracers in the sinusoidal bed indicates that zymosan induces the formation of permeability barriers, which could make the access of the solutes to transporters or enzymes located on the outer surface of the plasma membrane difficult.

A new method of quantifying glutathione levels in freshly isolated single superfused rat cardiomyocytes

Introduction: Glutathione (GSH) is an important antioxidant in the heart whose content changes during cardiac insults. However, there are currently no methods for continuously monitoring free cytoplasmic GSH levels in single isolated and superfused cardiomyocytes exposed to normal and pathological conditions. Methods: GSH was measured using CellTracker™ Blue CMAC (Molecular Probes), a member of a new family of thiol-sensitive dyes. The fluorescence of 5 μM CellTracker™ Blue CMAC was measured in various solutions containing glutathione- S-transferase and in freshly isolated single superfused cardiomyocytes using an inverted fluorescence microscope. The cardiomyocytes were isolated by standard procedures and loaded with either CellTracker™ Blue CMAC or monochlorobimane by 15 min of shaking incubation in the dark at room temperature followed by centrifugation with resuspension of the cells in dye-free media. Cell volume was calculated from the 3H 2O and [ 14C]sucrose space. Results: CellTracker™ Blue CMAC fluorescence was linearly proportional to 0–100 μM GSH, as described by the equation: Y=182.2 ( X)+681.6 ( r 2=.99, P<.001). Fluorescence was not affected by changing the glutathione- S-transferase level, the calcium concentration, or the pH, neither was the fluorescence quenched by H 2O 2 or cyanide. Exposure of freshly isolated single superfused cardiomyocytes to oxidative stress in the presence of 0–1 mM H 2O 2 caused a progressive decrease in cellular GSH. In contrast, brief exposure to metabolic inhibition in the presence of 2.5 mM NaCN evoked a significant increase in cardiomyocyte GSH followed by a return to control levels during washoff. In comparison to monochlorobimane, cells loaded with CellTracker™ Blue CMAC gave a stronger signal with better cellular retention of the probe. Discussion: These results suggest that CellTracker™ Blue CMAC fluorescence will be a good tool for measuring GSH in freshly isolated single superfused cardiomyocytes because it shows the expected changes to oxidative stress and metabolic inhibition, and is reversible.

Quantitative evaluation of altered hepatic spaces and membrane transport in fibrotic rat liver

Four animal models were used to quantitatively evaluate hepatic alterations in this study: (1) a carbon tetrachloride control group (phenobarbital treatment only), (2) a CCl 4-treated group (phenobarbital with CCl 4 treatment), (3) an alcohol-treated group (liquid diet with alcohol treatment), and (4) a pair-fed alcohol control group (liquid diet only). At the end of induction, single-pass perfused livers were used to conduct multiple indicator dilution (MID) studies. Hepatic spaces (vascular space, extravascular albumin space, extravascular sucrose space, and cellular distribution volume) and water hepatocyte permeability/surface area product were estimated from nonlinear regression of outflow concentration versus time profile data. The hepatic extraction ratio of 3H-taurocholate was determined by the nonparametric moments method. Livers were then dissected for histopathologic analyses ( e.g., fibrosis index, number of fenestrae). In these 4 models, CCl 4-treated rats were found to have the smallest vascular space, extravascular albumin space, 3H-taurocholate extraction, and water hepatocyte permeability/surface area product but the largest extravascular sucrose space and cellular distribution volume. In addition, a linear relationship was found to exist between histopathologic analyses (fibrosis index or number of fenestrae) and hepatic spaces. The hepatic extraction ratio of 3H-taurocholate and water hepatocyte permeability/surface area product also correlated to the severity of fibrosis as defined by the fibrosis index. In conclusion, the multiple indicator dilution data obtained from the in situ perfused rat liver can be directly related to histopathologic analyses. (H EPATOLOGY 2002;36:1180-1189.)

Stress-induced increase in extracellular sucrose space in rats is mediated by nitric oxide

Exposure to physical or psychological stress causes brain damage ranging from minimal behavioural alterations to neurodegeneration. One of the proposed mechanisms for stress-induced neurodegeneration is the overproduction of nitric oxide (NO) and related oxidative–nitrosative compounds via expression of the inducible NO synthase (iNOS). In the present investigation, the effect of acute or chronic immobilisation on blood–brain barrier (BBB) permeability and the possible role of iNOS were studied in adult male Wistar rats. Stress-induced [ 14C]-sucrose uptake by brain tissue correlates with the production of the stable NO metabolites nitrite and nitrate in both peripheral (plasma) and central (brain) compartments. Injection of the specific iNOS inhibitor 1400W (2 mg/kg, i.p.) prevents the stress-induced increase in BBB permeability. Taken together, these findings indicate that iNOS expression mediates stress-induced increase in BBB permeability and support a possible neuroprotective role for specific iNOS inhibitors in this situation.

Assessment by D-[3H]mannoheptulose uptake of B-cell density in isolated pancreatic islets from Goto-Kakizaki rats

The uptake of D-[3H]mannoheptulose by isolated pancreatic islets was recently proposed as a tool to assess the relative contribution of insulin-producing cells to the total mass of the islets. In the present study, the uptake of the tritiated heptose over 60 min incubation at 37 degrees C was about 21% lower in islets from hereditarily diabetic rats (GK rats) than in islets from control animals, this decrease being virtually identical to that documented previously by morphometric analysis of islets from the same type of rats. The intracellular 3HOH space and extracellular [U-14C]sucrose space were not significantly different in control and diabetic rats, at least when the comparison was restricted to animals of the same sex. There was a trend, however, towards a somewhat lower D-[5-3H]-glucose intracellular distribution space in islets from GK rats, as compared to control animals. These findings provide further support to the validity of D-[3H]mannoheptulose uptake as a tool to assess the density of insulin-producing cells in isolated islets.

Electrical permeabilization of rat luteal cells: In situ phosphorylation of endogenous proteins

Progesterone synthesis in the corpus luteum is regulated primarily by luteinizing hormone which acts via the adenylate cyclase/cyclic AMP/protein kinase A signalling cascade. Protein phosphorylation therefore plays a key role in the regulation of steroidogenesis, but there are relatively few studies of the in situ phosphorylation of luteal cell substrates. This may in part reflect the difficulties inherent in measuring changes in protein phosphorylation in intact cells preloaded with 32P and difficulties in interpreting data obtained using broken cell preparations. We have now applied a method of stable permeabilization of luteal cell plasma membranes by exposure of cell populations to a high intensity electric field. Under optimum conditions (5 kV/cm, six discharges) electrical permeabilization reproducibly produced populations of luteal cells in which 70–80% of the cells were permeabilized, as assessed by Trypan blue exclusion and [ 14C]sucrose space measurements. Pores were stable for at least 1 h, and there were no ultrastructural changes to the cells that could be detected by transmission electron microscopy. Permeabilized cells showed rapid cyclic AMP-induced changes in phosphorylation of endogenous proteins when provided with [γ- 32P]ATP. Our results demonstrate that the electrically permeabilized luteal cell offers a useful model for studying intracellular events in steroidogenic stimulus-response coupling cascades.

Prediction of macromolecular transport through the deformable porous media of an artery wall by pore theory

To determine the transport properties of macromolecules in the media of an artery wall deformed inhomogeneously by the transmural pressure, we combine a simple mechano-hydraulic model based on a two parameter strain-dependent permeability function, which was developed by Klanchar and Tarbell [1987], with a pore theory. The combined theory allows us to calculate the spatial distributions of porosity, solute partition, pore radius and macromolecuiar solute concentration in the media and their dependence on the transmural pressure. The predictions from the pore theory are in good agreement with experimental measurements of sucrose space, albumin space and albumin concentration profiles in the media of rabbit aortas at transmural pressures of 70 and 180 mmHg. The prediction indicates that albumin transport through the aortic media is dominated by convection rather than diffusion. It is further demonstrated that the transport properties of planar tissue samples, which are often used inin vitro experimentais, may be quile different from those of intact vessels in their natural cylindrical configuration because of the variation in tissue deformation. Using the pore theory we are also able to calculate the interstitial shear stress associated with transmural volume flow which may act on the smooth muscle cells residing in the media and find it to be on the order of several dyne/cm2. This level of shear stress will stimulate endothelial cells and may also affect smooth muscle cells.

Macromolecular transport through the deformable porous media of an artery wall.

To determine the macromolecular transport properties of the tunica media of an artery wall deformed inhomogeneously by the transmural pressure, we combine a simple mechano-hydraulic model based on a two parameter strain-dependent permeability function, which was developed by Klanchar and Tarbell (1987), with a fiber matrix theory. The combined theory allows us to calculate the spatial distributions of porosity, solute partition, fiber radius and macromolecular solute concentration in the media and their dependence on the transmural pressure. The predictions from the combined theory are in good agreement with experimental measurements of sucrose space, albumin space and albumin concentration profiles in the media of rabbit aortas at transmural pressures of 70 and 180 mmHg. The predictions indicate that albumin transport through the aortic media is dominated by convection rather than diffusion. It is further demonstrated that the transport properties of unstressed planar tissue samples, which are often used in in vitro experiments, may be quite different from those of intact vessels in their natural cylindrical configuration because of variation in tissue deformation.

Fluid-phase endocytosis by in situ cardiac myocytes of rat atria

Fluid-phase endocytosis (FPE) associated with recycling of fused plasmalemma-secretory granules or membranes and/or membrane receptors by in situ cardiac myocytes was studied at 37 degrees C in vitro noncontracting adult rat atrial preparations. Measurements included 1) the volume (VS*) of the compartment consisting of presumptive endocytotic vesicles and the endosomes or lysosomes transiently in continuity with them (S*), which internalizes [14C]-sucrose but is inaccessible to simultaneously measured [methoxy-3H]inulin, 2) the kinetics of [14C]sucrose efflux from S*, and 3) morphometry to quantify interstitial space and non-heart muscle cells. Vs* (0.39 +/- 0.04 ml/g dry atrium for unstretched atria at 37 degrees C) was 1) variable over a 3.7-fold range under various experimental conditions, 2) significantly increased by neomycin or by lowering the temperature to 18 degrees C, and 3) significantly decreased by alpha 1-adrenergic stimulation. Analysis of sucrose efflux kinetics confirmed the presence of an intramyocytic sucrose-containing compartment. A smaller inulin-inaccessible sucrose space (S*) was also present in right ventricle. Thus, during FPE, vesicles and endosomes initially containing high (extracellular) Ca2+ and Cl- concentrations continually enter, circulate within, and undergo exocytosis from myocardial cells.

Brain adaptation to chronic hypobaric hypoxia in rats.

Rats were exposed to hypobaric hypoxia (0.5 atm) for up to 3 wk. Hypoxic rats failed to gain weight but maintained normal brain water and ion content. Blood hematocrit was increased by 48% to a level of 71% after 3 wk of hypoxia compared with littermate controls. Brain blood flow was increased by an average of 38% in rats exposed to 15 min of 10% normobaric oxygen and by 23% after 3 h but was not different from normobaric normoxic rats after 3 wk of hypoxia. Sucrose space, as a measure of brain plasma volume, was not changed under any hypoxic conditions. The mean brain microvessel density was increased by 76% in the frontopolar cerebral cortex, 46% in the frontal motor cortex, 54% in the frontal sensory cortex, 65% in the parietal motor cortex, 68% in the parietal sensory cortex, 68% in the hippocampal CA1 region, 57% in the hippocampal CA3 region, 26% in the striatum, and 56% in the cerebellum. The results indicate that hypoxia elicits three main responses that affect brain oxygen availability. The acute effect of hypoxia is an increase in regional blood flow, which returns to control levels on continued hypoxic exposure. Longer-term effects of continued moderate hypoxic exposure are erythropoiesis and a decrease in intercapillary distance as a result of angiogenesis. The rise in hematocrit and the increase in microvessel density together increase oxygen availability to the brain to within normal limits, although this does not imply that tissue PO2 is restored to normal.

Venous pressure and bone formation

We have studied the relationship of increased venous pressure to formation of periosteal new bone in growing dogs. The methods used were measurement of fluid spaces in bone by steady-state tracer techniques, measurement of venous pressure, and measurement of the rate of periosteal new bone formation by histomorphometry. The results of paired comparisons—test versus control tibia—show an increase in venous pressure, a decrease in vascular space, an increase in extracellular fluid space (sucrose space), and an increase in periosteal new bone formation on the side of increased venous pressure. The data support the hypothesis that an increase in venous pressure results in an increase in passage of fluid from capillary to bone matrix. Increased extravascular perfusion could be a factor in increasing periosteal bone formation. This flux of fluid may increase streaming potentials in bone and these act as a signal to bone cells to increase bone formation.

The rat liver microcirculation in alcohol-induced hepatomegaly.

It has been suggested that hepatocyte enlargement can lead to compression of the extracellular space (sinusoidal and interstitial) and induce portal hypertension. However, this hypothesis has never been tested by measuring the vascular and extravascular spaces in the intact liver. The aim of the present study was to investigate the effects of chronic alcohol intake on the hepatic microcirculation using Goresky's multiple-indicator dilution technique in the isolated perfused rat liver. Female rat littermates were pair-fed either ethanol (n = 7) or an isocaloric carbohydrate diet (n = 7) for 21 days. As expected, chronic alcohol intake produced a significant increase in liver/body weight ratio (+32%, p less than 0.01) and hepatocyte size (+45%, p less than 0.001), which was accompanied by a marked increase in the cellular water space (control: 3.3 +/- 0.6 ml; ethanol-fed: 4.9 +/- 0.9 ml; p less than 0.001). When expressing data per total liver, the sinusoidal space was similar in the two groups (control: 1.87 +/- 0.2; ethanol-fed: 1.95 +/- 0.2 ml; not significant), whereas the interstitial space was increased in alcohol rats compared to controls (albumin space +58%, p less than 0.01; sucrose space +51%, p less than 0.01). In alcoholic rats, the sinusoidal space was probably stretched, with an overall reduced transversal diameter, as suggested by the reduced values found when data were expressed per gm of liver weight. However, despite this finding and the enlargement of the liver and hepatocytes observed in alcoholic rats, similar values were obtained between the two groups for the portal perfusion pressure and thus the intrahepatic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

POSTNATAL WEIGHT LOSS AND REGAINING OF BIRTH WEIGHT IN VLBW INFANTS REFLECT EXTRACELLULAR VOLUME CHANGES AND NOT NUTRITIONAL STATUS

Do initial weight changes under the usual restrictive fluid therapy in premature infants reflect water balance or nutritional status? We studied in 8 premature infants (GA 26-29 wks, on respirator) total body water TBW (D2O space),body solids (weight-TBW), extracellular volume ECV (sucrose space) and intracellular volume ICV (TBW-ECV) at birth, at maximal weight loss and when birth weight was regained. Weight (-79g), TBW (-95ml) and ECV (-80ml) initially decreased (p<:*0.01;**0.001), body solids and ICV did not change. During subsequent weight gain there was a trend of TBW and ECV to return to initial levels. Caloric intake was borderline to meet basal metabolic needs, but even at study end not sufficient for growth.Conclusion: Postnatal weight loss is loss of body water from the ECV, subsequent weight gain is restauration of fluid volumes towards initial levels.

Increased sinusoidal volume and solute extraction during retrograde liver perfusion.

Retrograde isolated liver perfusion has been used to probe acinar functional heterogeneity, but the hemodynamic effects of backward flow have not been characterized. In this study, extraction of a long-chain fatty acid derivative, 12-N-methyl-7-nitrobenzo-2-oxa-1,3-diazol-amino stearate (12-NBDS), was greater during retrograde than during anterograde perfusion of isolated rat liver. To determine whether hemodynamic differences between anterograde and retrograde perfused livers could account for this finding, the hepatic extracellular space was measured for both directions of flow by means of [14C]sucrose washout during perfusion as well as by direct measurement of [14C]sucrose entrapped during perfusion. A three- to fourfold enlargement of the total hepatic extracellular space was found during retrograde perfusion by both approaches. Examination of perfusion-fixed livers by light microscopy and morphometry revealed that marked distension of the sinusoids occurred during retrograde perfusion and that this accounts for the observed increase in the [14C]sucrose space. These findings support the hypothesis that maximum resistance to perfusate flow in the isolated perfused rat liver is located at the presinusoidal level. In addition, increased transit time of perfusate through the liver and greater sinusoidal surface area resulting from sinusoidal distension may account for the higher extraction of 12-NBDS and possibly other compounds by retrograde perfused liver.

Effect of pressure and intimal damage on 131I-albumin and [14C]sucrose spaces in aorta.

To measure the distribution volume for sucrose and albumin in the media of the rabbit thoracic aorta, we studied the uptake of tracers in vitro. In most cases the tracers were applied to both luminal and adventitial surfaces at the same concentration. When transmural convection was prevented by pressurization of the arteries with air, there was a decrease in sucrose space (19% at 70 mmHg and 28% at 180 mmHg) and in albumin space (60% at 70 mmHg and 66% at 180 mmHg), compared with the respective spaces in relaxed arteries (0.42 for sucrose and 0.08 for albumin). Much smaller changes were found when intact vessels were pressurized with liquid (insignificant for sucrose, decreases of 24% at 70 mmHg and 14% at 180 mmHg for albumin). Removal of the endothelium, which increases transmural fluid flux, increased the space for sucrose (not significantly at 70 mmHg and 17% at 180 mmHg) and particularly for albumin (100% at 70 mmHg and 250% at 180 mmHg). We conclude that the interstitial volume and consequently the protein space within the media can be modified both by distending stresses applied to the vessel and by transmural fluid flux.

Early disturbance of calcium translocation across the plasma membrane in toxic liver injury.

An increased influx and/or a decreased extrusion of calcium across the plasma membrane resulting in an increase in cytosolic-free calcium could play an important role in the initiation of irreversible cell injury. Therefore, the translocation of calcium across the plasma membrane was probed in the perfused rat liver using multiple indicator dilution methodology. The sucrose space corresponding to the extracellular space amounted to 0.35 +/- 0.13 ml per gm liver, and the water space corresponding to the extra- and intracellular spaces was 0.97 +/- 0.08 ml per gm. The calcium space was always slightly larger (0.42 +/- 0.10 ml per gm) than the sucrose space. The calcium space further increased during perfusion with the calcium ionophore A 23187, whereas the sucrose space remained unchanged. Two hours after administration to intact rats of acetaminophen (2 gm per kg) and carbon tetrachloride (2 ml per kg), respectively, the calcium space had increased markedly relative to the sucrose space and relative to the water space, indicating an increased accessibility of the cells to extracellular calcium. Similarly, reperfusion of livers after 90 min of ischemia was associated with an increase in calcium space relative to the sucrose and water spaces. These studies indicate that, in three models of acute liver injury, the net influx of calcium across the plasma membrane is increased early in the evolution of the injury before irreversible damage occurs.