Genetic inheritance of gene expression in human cell lines

Combining genetic inheritance information, for both molecular profiles and complex traits, is a promising strategy not only for detecting quantitative trait loci (QTLs) for complex traits but for understanding which genes, pathways, and biological processes are also under the influence of a given QTL. As a primary step in determining the feasibility of such an approach in humans, we present the largest survey to date, to our knowledge, of the heritability of gene-expression traits in segregating human populations. In particular, we measured expression for 23,499 genes in lymphoblastoid cell lines for members of 15 Centre d'Etude du Polymorphisme Humain (CEPH) families. Of the total set of genes, 2,340 were found to be expressed, of which 31% had significant heritability when a false-discovery rate of 0.05 was used. QTLs were detected for 33 genes on the basis of at least one P value <.000005. Of these, 13 genes possessed a QTL within 5 Mb of their physical location. Hierarchical clustering was performed on the basis of both Pearson correlation of gene expression and genetic correlation. Both reflected biologically relevant activity taking place in the lymphoblastoid cell lines, with greater coherency represented in Kyoto Encyclopedia of Genes and Genomes database (KEGG) pathways than in Gene Ontology database pathways. However, more pathway coherence was observed in KEGG pathways when clustering was based on genetic correlation than when clustering was based on Pearson correlation. As more expression data in segregating populations are generated, viewing clusters or networks based on genetic correlation measures and shared QTLs will offer potentially novel insights into the relationship among genes that may underlie complex traits.

Futile cycles revisited: a markov chain model of simultaneous glycolysis and gluconeogenesis

We have used a random walk model of glycolysis and gluconeogenesis to investigate the bioenergetic implications of considering the cell cytoplasm to be a uniform well-mixed compartment. Radiotracer studies conducted on hepatocytes harvested from fasted rats and incubated with 40 mM glucose and 10 mM lactate demonstrated simultaneous glycolysis and gluconeogenesis, with net glycolysis. Tracer introduced as glycerol was incorporated both into glucose (via gluconeogenesis) and into pyruvate (via glycolysis). The data allow us to place a lower bound on the energetic cost of futile cycles involving adenosine triphosphate (ATP) hydrolysis in the early phosphorylation steps of glycolysis. Applying the Markov Chain model for glucose undergoing metabolism to pyruvate, the expected number of ATP molecules hydrolysed is not less than 15 ATP molecules per glucose molecule. The data suggest that, in hepatocytes under the circumstances of this experiment, either glycolysis is a net consumer of ATP, or glycolysis and gluconeogenesis are compartmentalized to a greater extent than is generally supposed.

A benefit of one's own: older women's entitlement to Social Security retirement

This article explores differences in Social Security eligibility and benefit levels for older men and women using survey data from the Health and Retirement Study combined with administrative records on actual work histories and Social Security rules. We are able to determine the fully insured status of those persons, how close they are to meeting eligibility criteria when they are not fully insured, and their prospects for benefits. Around three-quarters of older women nearing retirement today will be fully insured for Social Security old-age benefits on the basis of their own accounts, but the rest would need substantial extra employment to rise above the eligibility threshold. Further, two-thirds of older married women who are fully insured have sufficient lifetime earnings to translate into an age-65 primary insurance amount worth at least half their husband's, but the other one-third can expect no additional retirement benefit from contributing to Social Security late in life. Finally, most wives will not be able to improve their benefits by working more under current rules. These results have mixed implications regarding the potential impact of women's rising labor force attachment on eventual retirement benefits. Working more years could increase women's chances of becoming eligible for Social Security benefits, but that effect is likely to be small. Furthermore, even when women do become fully insured according to the rules, not many wives will receive a higher benefit at the margin. The reason is that married women still receive higher Social Security benefits as a spouse than they do on the basis of their own work record. In fact, the net benefit from Social Security due to additional work is negative once one takes into account the Social Security contributions the women paid while employed. Benefits paid to widows are even more likely to be based on the spouse's work history rather than on the woman's. Hence, the rising labor market attachment of women in the future may increase their eligibility for benefits but will produce only modest (and often negative) impacts on their old-age Social Security benefits under current rules.

AP-3 adaptor functions in targeting P-selectin to secretory granules in endothelial cells

P-selectin, a cell adhesion protein participating in the early stages of inflammation, contains multiple sorting signals that regulate its cell surface expression. Targeting to secretory granules regulates delivery of P-selectin to the cell surface. Internalization followed by sorting from early to late endosomes mediates rapid removal of P-selectin from the surface. We show here that the P-selectin cytoplasmic domain bound AP-2 and AP-3 adaptor complexes in vitro. The amino acid substitution L768A, which abolishes endosomal sorting and impairs granule targeting of P-selectin, reduced binding of AP-3 adaptors but not AP-2 adaptors. Turnover of P-selectin was 2.4-fold faster than turnover of transferrin receptor in AP-3-deficient mocha fibroblasts, similar to turnover of these two proteins in AP-3-competent cells, demonstrating that AP-3 function is not required for endosomal sorting. However, sorting P-selectin to secretory granules was defective in endothelial cells from AP-3-deficient pearl mice, demonstrating a role for AP-3 adaptors in granule assembly in endothelial cells. P-selectin sorting to platelet alpha-granules was normal in pearl mice, consistent with earlier evidence that granule targeting of P-selectin is mechanistically distinct in endothelial cells and platelets. These observations establish that AP-3 adaptor functions in assembly of conventional secretory granules, in addition to lysosomes and the 'lysosome-like' secretory granules of platelets and melanocytes.

Effect of creatine supplementation on metabolism and performance in humans during intermittent sprint cycling

This double blind study investigated the effect of oral creatine supplementation (CrS) on 4 x 20 s of maximal sprinting on an air-braked cycle ergometer. Each sprint was separated by 20 s of recovery. A group of 16 triathletes [mean age 26.6 (SD 5.1) years. mean body mass 77.0 (SD 5.8) kg, mean body fat 12.9 (SD 4.6)%, maximal oxygen uptake 4.86 (SD 0.7) l.min-1] performed an initial 4 x 20 s trial after a muscle biopsy sample had been taken at rest. The subjects were then matched on their total intramuscular creatine content (TCr) before being randomly assigned to groups to take by mouth either a creatine supplement (CRE) or a placebo (CON) before a second 4 x 20 s trial. A muscle biopsy sample was also taken immediately before this second trial. The CrS of 100 g comprised 4 x 5 g for 5 days. The initial mean TCr were 112.5 (SD 8.7) and 112.5 (SD 10.7) mmol.kg-1 dry mass for CRE and CON, respectively. After creatine loading and placebo ingestion respectively, CRE [128.7 (SD 11.8) mmol.kg-1 dry mass] had a greater (P = 0.01) TCr than CON [112.0 (SD 10.0) mmol.kg-1 dry mass]. While the increase in free creatine for CRE was statistically significant (P = 0.034), this was not so for the changes in phosphocreatine content [trial 1: 75.7 (SD 6.9), trial 2: 84.7 (SD 11.0) mmol.kg-1 dry mass, P = 0.091]. There were no significant differences between CRE and CON for citrate synthase activity (P = 0.163). There was a tendency towards improved performance in terms of 1 s peak power (in watts P = 0.07; in watts per kilogram P = 0.05), 5 s peak power (in watts P = 0.08) and fatigue index (P = 0.08) after CrS for sprint 1 of the second trial. However, there was no improvement for mean power (in watts P = 0.15; in watts per kilogram P = 0.1) in sprint 1 or for any performance values in subsequent sprints. Our results suggest that, while CrS elevates the intramuscular stores of free creatine, this does not have an ergogenic effect on 4 x 20 s all-out cycle sprints with intervening 20-s rest periods.

Experimental annotation of the human genome using microarray technology

The most important product of the sequencing of a genome is a complete, accurate catalogue of genes and their products, primarily messenger RNA transcripts and their cognate proteins. Such a catalogue cannot be constructed by computational annotation alone; it requires experimental validation on a genome scale. Using 'exon' and 'tiling' arrays fabricated by ink-jet oligonucleotide synthesis, we devised an experimental approach to validate and refine computational gene predictions and define full-length transcripts on the basis of co-regulated expression of their exons. These methods can provide more accurate gene numbers and allow the detection of mRNA splice variants and identification of the tissue- and disease-specific conditions under which genes are expressed. We apply our technique to chromosome 22q under 69 experimental condition pairs, and to the entire human genome under two experimental conditions. We discuss implications for more comprehensive, consistent and reliable genome annotation, more efficient, full-length complementary DNA cloning strategies and application to complex diseases.

The isolated hepatocyte preparation: 30 years on

A method for the preparation of intact rat hepatocytes in high yield was first described in 1969. The procedure involved digestion of hepatic tissue by perfusion of the liver with crude collagenase; later, purified collagenase without other enzymic additions was shown to be ineffective. Recently it has been discovered that the combination of purified collagenase plus elastase is superior to crude collagenase in that it consistently provides high yields of undamaged hepatocytes. The isolated hepatocyte preparation has proved particularly useful for the study of mechanisms responsible for long-range interactions within the cell. These can be studied over prolonged time courses and in the presence of graded concentrations of specific inhibitors. Studies of this kind have demonstrated a close relationship between cytoplasmic metabolic flows and mitochondrial forces and have also revealed that the cytoplasmic and mitochondrial free NAD-linked redox potentials are maintained by energy-dependent reactions.

Hepatic glucose cycling does not contribute to the development of hyperglycemia in Zucker diabetic fatty rats

Hepatic glucose cycling, whereby glucose is taken up by the liver, partially metabolized, then recycled to glucose, makes a substantial contribution to the development of hyperglycemia in IDDM. This stimulation of glucose cycling appears to be associated with elevated rates of fatty acid oxidation. Whether hepatic glucose cycling also contributes to the development of hyperglycemia in NIDDM is unclear. Using a model of NIDDM, the Zucker diabetic fatty (ZDF) rat, we determined whether glucose cycling was enhanced. Hepatocytes from ZDF rats exhibited higher rates of glucose phosphorylation and glycolysis, but there was no increase in the rate of cycling between glucose and glucose-6-phosphate or between glycolytically derived pyruvate and glucose. Despite the increased rates of glycolysis, the production of CO2 in liver cells from ZDF rats was no different from rates measured in cells from control animals. Instead, there was a large increase in the accumulation of lactate and pyruvate in the ZDF liver cells. The addition of 2-bromopalmitate, an inhibitor of fatty acid oxidation that inhibited glucose cycling in hepatocytes from IDDM rats, had no effect on glucose cycling in cells from ZDF rats. We therefore conclude that, unlike in IDDM, hepatic glucose cycling does not contribute to the development of hyperglycemia in the NIDDM Zucker rat.

Long-term maintenance of low concentrations of fructose for the study of hepatic glucose phosphorylation

The stimulation of glucose phosphorylation in isolated hepatocytes by low fructose concentrations is transient due to the rapid metabolism of fructose. To prolong this stimulatory effect fructose was enzymically generated in the incubation medium from either sucrose with invertase or inulin with inulinase. A maximal rate of glucose phosphorylation was achieved when fructose was formed at at least 0.01 micromol/min, which maintained a concentration of 70 microM fructose in the medium. In the presence of a fructose concentration of 70 microM, the rate of phosphorylation with 5 mM glucose was doubled and remained constant over a 2.5 h period. Under these conditions the rate of glycolysis was increased more than 3-fold. The stimulation of flux through glucokinase by low concentrations of fructose decreased the proportion of glucose phosphorylated, which was cycled between glucose and glucose 6-phosphate, and increased the proportion that was glycolysed. The method described for maintaining the stimulation of glucose phosphorylation by isolated hepatocytes over prolonged incubation periods is especially suited to the further study of the control of glucokinase activity, in particular how the variation of flux through glucokinase affects the flux through all the pathways that utilize the product, glucose 6-phosphate.

Differential induction of chromosomal instability by DNA strand-breaking agents

To investigate the role of DNA strand breakage as the molecular lesion responsible for initiating genomic instability, five different strand-breaking agents, bleomycin, neocarzinostatin, hydrogen peroxide, restriction endonucleases, and ionizing radiation, were examined for their capacity to induce delayed chromosomal instability. These studies used GM10115 human-hamster hybrid cells, which contain one copy of human chromosome 4 in a background of 20-24 hamster chromosomes. Chromosomal instability was investigated using fluorescence in situ hybridization to visualize chromosomal rearrangements involving the human chromosome. Rearrangements are detected multiple generations after treatment, in clonal populations derived from single progenitor cells surviving treatment of the specified DNA-damaging agents. Clastogenic and cytotoxic activities of all agents were tested by examining chromosome aberration yields in first-division metaphases and by clonogenic survival assays. Analysis of over 250 individual clones representing over 50,000 metaphases demonstrates that when compared at comparable levels of cell kill, ionizing radiation, bleomycin, and neocarzinostatin are equally effective at eliciting delayed genomic instability. These observations document, for the first time, the persistent destabilization of chromosomes following chemical treatment. In contrast, the analysis of nearly 300 clones and 60,000 metaphases, involving treatment with four different restriction endonucleases and/or hydrogen peroxide, did not show any delayed chromosomal instability. These data indicate that DNA strand breakage per se does not necessarily lead to chromosomal instability but that the complexity or quality of DNA strand breaks are important in initiating this phenotype.

Isolated hepatocytes--past, present and future

The first technique for large-scale preparation of isolated hepatocytes was described in 1953 and involved perfusion of rat liver under pressure with a Ca(2+)-free solution containing a chelating agent. Various modifications of this technique were in use over the next ten years, until it was demonstrated that cells prepared in this manner were grossly damaged, losing most of their cytoplasmic enzymes during the preparative procedure. The successful preparation of intact isolated hepatocytes by collagenase-treatment of liver was achieved in 1967, and the widespread use of intact hepatocyte suspensions was accelerated by the development soon after of high-yield preparative techniques involving perfusion of the liver with a medium containing collagenase. The introduction of the isolated hepatocyte preparation has enabled experimental studies that otherwise would not be feasible. Important advances have been the use of cultured hepatocytes, frequently of human origin, for the investigation of the metabolism and toxicology of potential therapeutic agents. Success in this field has been achieved through the steady improvement in techniques for the maintenance in culture of differentiated hepatocytes, and in particular their cytochrome P450 complexes. Another area showing considerable promise is the employment of hepatocytes, generally from a porcine source, in temporary support systems for patients with acute liver failure. Our own studies have concentrated on the demonstration of long-range interactions between hepatocyte compartments which suggest that energy transfer between cell compartments can take place without ATP turnover.

MEG-based imaging of focal neuronal current sources

We describe a new approach to imaging neural current sources from measurements of the magnetoencephalogram (MEG) associated with sensory, motor, or cognitive brain activation. Many previous approaches to this problem have concentrated on the use of weighted minimum norm (WMN) inverse methods. While these methods ensure a unique solution, they do not introduce information specific to the MEG inverse problem, often producing overly smoothed solutions and exhibiting severe sensitivity to noise. We describe a Bayesian formulation of the inverse problem in which a Gibbs prior is constructed to reflect the sparse focal nature of neural current sources associated with evoked response data. We demonstrate the method with simulated and experimental phantom data, comparing its performance with several WMN methods.

Who takes early Social Security benefits? The economic and health characteristics of early beneficiaries

Using the 1992 and 1994 Waves of the Health and Retirement Survey, we compare individuals who first take Social Security benefits at age 62 with those who don't and find that the income and net assets of these two groups are similar in the years just prior to eligibility. However, there is great diversity within the groups, so that poor health appears to be more closely related to lower economic well-being than is early Social Security acceptance status. Our results suggest that raising the Social Security retirement age is not likely to dramatically lower the economic well-being of the typical person aged 62 since only 3% of men aged 62 are receiving Social Security retirement benefits, are in poor health, and have Social Security retirement benefits as their only source of pension income.

Suppression of glycolysis is associated with an increase in glucose cycling in hepatocytes from diabetic rats

Rates of cycling between glucose and glucose 6-phosphate and between glucose and pyruvate, and the effects of these cycles on glucose metabolism, were compared in hepatocytes isolated from fasted normal or streptozotocin-induced diabetic rats. In diabetic hepatocytes the rate of glucose phosphorylation was 30% lower than that in normal hepatocytes, and there was a doubling of the rate of glucose/glucose 6-phosphate cycling. In addition, the rate of glycolysis was 60% lower in diabetic hepatocytes. This inhibition of glycolysis and stimulation of glucose/glucose 6-phosphate cycling appeared to be a consequence of the elevated rates of endogenous fatty acid oxidation observed in diabetic hepatocytes. The proportion of glycolytically derived pyruvate that was recycled to glucose was more than doubled in hepatocytes from diabetic rats compared with normal animals. This increase also appeared to be linked to the high rates of endogenous fatty acid oxidation in diabetic cells. As a consequence of the increased rates of both these cycles, 85% of all glucose molecules taken up by diabetic hepatocytes were recycled to glucose, compared with only 50% in normal hepatocytes. Glucose cycling is therefore likely to make a substantial contribution to the hyperglycemia of diabetes.

Strength of silicone breast implants

Rupture and leakage are recognized problems associated with silicone breast implants. Data are scarce about the durability of the silicone shell, and the life span of this device is unknown. The purpose of this study was to investigate the strength of silicone breast implants. Thirty implant shells were subjected to mechanical testing. Twenty-nine of the shells were tested after explanation, and one unused implant served as a control to validate the testing method. Implantation time varied from 4 months to 20 years, and all shells were tested, regardless of condition. Fourteen implant shells were intact, eight were leaking, and seven were ruptured. All ruptured implants had been in place for 10 years or longer. The breaking force of all excised shell specimens ranged from 2.6 to 22.4 N (0.6 to 5.0 lb.). Specimens from the control "high performance" shell required 15.5 to 25.6 N (3.5 to 5.8 lb) of force to fail. The weakest group was from thin-shelled implants between 10 and 16 years of age. More than half these specimens failed with less than 1 lb of force. The average breaking force of ruptured shell material was less than that of intact shells. A comparison of strength data in this study with manufacturers' data suggests that breaking force is dependent on implant type, shell thickness, and implantation time.

Effects of thyroid status on glucose cycling by isolated rat hepatocytes

The effects of alterations in thyroid status on glucose metabolism have been investigated in rat hepatocytes. Addition of 10 or 40 mmol/L glucose induced increases in respiration rate that were significantly larger in cells from hyperthyroid rats than from hypothyroid animals. The responses of hepatocytes from euthyroid rats were intermediate. In cells from hyperthyroid rats, most of the increase occurred upon addition of 10 mmol/L glucose, with only a further small stimulation resulting when glucose concentration was increased to 40 mmol/L. For a given glucose concentration, glycolytic rates, determined by measuring release of tritium from [6-3H]glucose, were comparable in all thyroid states. Studies with 10 mmol/L [2-3H]glucose showed that cycling between glucose-6-phosphate and glucose was almost twofold higher in euthyroid and hyperthyroid states as compared with the hypothyroid state, although the magnitude of the increase in cycling rate was only approximately 0.2 mumol glucose.min-1.g-1. When 40 mmol/L [2-3H]glucose was added, over 44% of the glucose that was phosphorylated to glucose-6-phosphate was cycled back to glucose, but this cycling was independent of thyroid status. Cycling between fructose-1,6-bisphosphate and fructose-6-phosphate was negligible in all thyroid states. Rates of glycogen synthesis were comparable in hypothyroid and hyperthyroid states and slightly less than in the euthyroid state. Glycolytically formed pyruvate was cycled back to glucose in hepatocytes from hypothyroid, euthyroid, and hyperthyroid rats. During a 60-minute incubation period, cycling to glucose in the presence of 10 mmol/L or 40 mmol/L glucose was up to twofold higher in cells from euthyroid and hyperthyroid rats than in hepatocytes from hypothyroid animals. The measured increases in cycling rates induced by thyroid hormone were small and in theory could have been satisfied by a much smaller increase in respiration rate than was observed.

Abolition of the inhibitory effect of ethanol oxidation on gluconeogenesis from lactate by asparagine or low concentrations of ammonia

When isolated hepatocytes from fasted rats were incubated with 10 mM lactate, the [lactate]/[pyruvate] ratio measured at the beginning of the incubation was raised above 70:1 but declined to a steady level of about 8:1 within 40 min. The rate of gluconeogenesis from lactate was initially slow but gradually increased over the incubation period becoming maximal by 30 min. The simultaneous addition of lactate and ethanol resulted in an initial [lactate]/[pyruvate] ratio above 250:1 which by 60 min had declined to a new steady-state level of approx. 60:1. The lactate, ethanol combination also brought about a prolongation of the lag phase before glucose synthesis became maximal; however, by 40 min the rate of gluconeogenesis was independent of the presence of ethanol. Thus the inhibitory effect of ethanol on glucose synthesis was manifest only over the early portion of the incubation period. When asparagine, a precursor of malate/aspartate components, was added to the incubation mixture, the lag before maximal rates of glucose formation from lactate in the absence or presence of ethanol was almost abolished. The presence of asparagine also rapidly lowered the [lactate]/[pyruvate] ratio of hepatocytes incubated with lactate plus ethanol establishing a steady-state level of 15:1 within 10-15 min. Asparagine enhanced the rate of lactate-stimulated ethanol oxidation, particularly during the early part of the incubation. In endeavouring to elucidate which of the products of asparagine catabolism (i.e. ammonia and aspartate) were responsible for these effects, we found that a small and constant level of ammonia, formed by the degradation of urea by urease, almost reproduced the effects of asparagine on the [lactate]/[pyruvate] ratio, glucose synthesis and ethanol oxidation. A bolus addition of 10 mM aspartate or 4 mM ammonia to cells metabolising lactate and ethanol were less effective than a steady-state low ammonia concentration, generated from urea/urease. Our studies suggest that asparagine or a low concentration of ammonia, by providing components of the malate/aspartate shuttle, can ameliorate some of the metabolic effects of ethanol on the liver.

Stimulation of gluconeogenesis leads to an increased rate of beta-oxidation in hepatocytes from fasted diabetic but not from fasted normal rats

We have investigated the effects of imposing an ATP demand, generated by the addition of lactate, on hepatocytes isolated from fasted normal and streptozocin-induced diabetic rats. The stimulation of O2 consumption upon lactate addition was much greater in hepatocytes from diabetic rats, as a result of a lactate-induced stimulation of beta-oxidation that was not observed in control cells. This lactate-induced increment in beta-oxidation was extremely sensitive to inhibition by low levels of a number of inhibitors of energy transduction, implying that the increment was tightly coupled to ATP synthesis. Such sensitivity of the beta-oxidative pathway to the addition of similar low concentrations of these inhibitors was not seen in control cells. Inhibitors of the gluconeogenic pathway were also more effective in decreasing beta-oxidation in cells from diabetic animals than in cells from normal rats. The increment in beta-oxidation was not accompanied by increased rates of glucose synthesis, fatty acid esterification or ureogenesis. We propose that it may be associated with higher rates of glucose cycling in cells from diabetic rats.

The contribution of glucose cycling to the maintenance of steady-state levels of lactate by hepatocytes during glycolysis and gluconeogenesis

When hepatocytes from fasted rats were incubated with 10 mM glucose, there was a linear accumulation of lactate and pyruvate for about 80 min after which steady-state concentrations of these metabolites became established. The rate of glycolysis, determined with [6-3H]glucose, was constant over the entire incubation period and was 50% greater than that calculated from carbon balance studies. This suggests that one-third of the glycolytic products formed were recycled to glucose. To enable study of the factors associated with the generation and maintenance of the lactate steady state and to measure accurately the carbon balance, incubations were performed using supraphysiological concentrations of glucose (20-80 mM). Under these conditions the initial rate of lactate accumulation and its concentration at steady state were shown to be dependent on the concentration of extracellular glucose. Rates of glycolysis were also measured using 40 mM [6-3H]glucose and [U-14C]glucose added alone, or in combination with a steady-state lactate concentration (3 mM). There was no effect on the rate of glycolysis determine with [6-3H]glucose, even when lactate was present in the medium. The difference in rates between measurements with the two isotopes reflect the apparent degree of glucose recycling which in the absence and presence of added lactate increased from 0.26 to 0.54 mumol C3 equivalents min-1.g-1 respectively. Identical studies employing [U-14C]lactate showed that glucose and CO2 were the major products of lactate metabolism under steady-state conditions and that the formation of lactate from [U-14C]glucose exactly balanced the rate of lactate removal as a result of oxidation and gluconeogenesis. These studies provide evidence for the concomitant operation of glycolysis and gluconeogenesis, even in the presence of high glucose concentrations. They also demonstrate that lactate steady states are achieved not by the cessation of glycolysis but rather by the removal of lactate and pyruvate at a rate equal to that of their production.

The capacity of reducing-equivalent shuttles limits glycolysis during ethanol oxidation

The inhibition of glycolysis during ethanol oxidation has been examined in isolated hepatocytes from fasted rats. Glycolytic flux was measured by determining the rate of release of tritium from [6-3H]glucose. During ethanol oxidation, the rate of glycolysis was inhibited 80% in freshly prepared hepatocytes, in which shuttle intermediates are depleted, but was depressed only about 20% in the presence of asparagine, a condition under which activity of the malate/aspartate shuttle was restored to normal levels. The inhibition of glycolysis was also partially released by addition of pyruvate and when alcohol dehydrogenase activity was depressed by 4-methylpyrazole. Titrations with this inhibitor revealed inverse linear relationships between the rates of glycolysis and ethanol oxidation. For any given rate of ethanol oxidation, glycolytic flux was lowest and the [lactate]/[pyruvate] ratio highest in the presence of aminooxyacetate, an inhibitor of the malate/aspartate shuttle, whereas flux was highest and the ratio lowest in the presence of asparagine. During these titrations with 4-methylpyrazole the inhibition of ethanol oxidation and concomitant restoration of glycolysis were accompanied by a decline in the [lactate]/[pyruvate] ratio, a substantial fall in the rate of reducing-equivalent transfer from cytoplasm to mitochondria and an increase in lactate accumulation. These findings imply that the reducing equivalents generated during ethanol oxidation compete with those arising in glycolysis for transfer to the mitochondria. This competition leads to an inhibition of aerobic glycolysis, and at the same time contributes to a rise in cytoplasmic NADH and fall in NAD+ that results in depression of anaerobic glycolysis. Allosteric inhibition of 6-phosphofructo-1-kinase due to a decrease in the concentration of fructose 2,6-bisphosphate did not appear to play a primary role in the inhibition of glycolysis by ethanol. Ethanol oxidation had no effect on glucose phosphorylation as measured with [2-3H]glucose, but induced a substantial increase in cycling between glucose and glucose 6-phosphate.

Illegitimate recombination induced by DNA double-strand breaks in a mammalian chromosome

We examined DNA double-strand-break-induced mutations in the endogenous adenine phosphoribosyl-transferase (APRT) gene in cultured Chinese hamster ovary cells after exposure to restriction endonucleases. PvuII, EcoRV, and StuI, all of which produce blunt-end DNA double-strand breaks, were electroporated into CHO-AT3-2 cells hemizygous at the APRT locus. Colonies of viable cells containing mutations at APRT were expanded, and the mutations that occurred during break repair were analyzed at the DNA sequence level. Restriction enzyme-induced mutations consisted of small deletions of 1 to 36 bp, insertions, and combinations of insertions and deletions at the cleavage sites. Most of the small deletions involved overlaps of one to four complementary bases at the recombination junctions. Southern blot analysis revealed more complex mutations, suggesting translocation, inversion, or insertion of larger chromosomal fragments. These results indicate that blunt-end DNA double-strand breaks can induce illegitimate (nonhomologous) recombination in mammalian chromosomes and that they play an important role in mutagenesis.

Effect of citrate infusion on urinary aluminium excretion in the rat

1. Seven pairs of rats received 1 mmol/l aluminium citrate in their drinking water 5 days before the experiments. Five additional rats were treated identically. Six rats received the same food but drank distilled water. 2. After a 6 h fast, the animal was anaesthetized, the jugular vein and femoral artery were cannulated and the bladder was catheterized, after which an intravenous infusion of Hartmann's solution containing [14C]inulin was begun. The urine was collected at 20 min intervals and 1 ml of arterial blood was obtained before the end of each collection. After at least two basal collections, the infusion was modified to contain, in addition, 5 mmol/l NaHCO3 (control) or 5 mmol/l sodium citrate (experimental). The infusion rate, constant in each pair, differed between pairs across the range 60-125 mumol/min. 3. A total of eight collections was made per animal and urine flow, glomerular filtration rate, plasma and urinary aluminium and citrate were measured. 4. Control and experimental rats had a higher mean basal plasma aluminium level (0.39 +/- 0.21 mumol/l) than the six rats receiving distilled water (0.16 +/- 0.14 mmol/l, P < 0.001). The corresponding urinary aluminium excretion rates were similar (46 +/- 31 and 47 +/- 23 pmol/min, respectively). There was no significant difference between the basal values of any variable in the control and experimental rats. No significant change was observed in any variable during the infusion of NaHCO3 (controls). Among the experimental rats, there was no significant change in urine flow, glomerular filtration rate or plasma aluminium level.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular resistance to oxidative stress is accompanied by resistance to cisplatin: the significance of increased catalase activity and total glutathione in hydrogen peroxide-resistant fibroblasts

Studies designed to better understand the involvement of cellular resistance to oxidative stress in mechanisms of cellular resistance to cisplatin were undertaken using H2O2-resistant variants of the HA1 Chinese hamster fibroblast cell line. H2O2-resistant cell lines were resistant to clonogenic inactivation mediated by cisplatin with dose modifying factors at 10% survival of 1.5-3.0, relative to HA1 cells. The most cisplatin resistant of these cell lines (OC5) also demonstrated fewer DNA-DNA crosslinks induced by cisplatin, relative to HA1. Since H2O2-resistant cells contained increased catalase activity as well as total glutathione (GSH) content, the involvement of these cellular antioxidants in the resistance to cisplatin toxicity was evaluated. Treatment of HA1 and H2O2-resistant cell lines (OC5, OC14) with 9 mM aminotriazole reduced catalase activity by 60-65% but had no effect on the cytotoxicity of cisplatin. In contrast, treatment with 5 mM buthionine sulfoximine reduced total GSH by 90% and sensitized the cells to cisplatin cytotoxicity. Furthermore, extracellular reaction of GSH with cisplatin prior to treating HA1 cells reduced the toxicity of the compound, indicating that this reaction is capable of participating in the detoxification of cisplatin. These results indicate that cellular adaptation to oxidative stress renders cells resistant to DNA damage as well as to cytotoxicity associated with cisplatin treatment. Furthermore, increases in total GSH content (but not catalase activity) appear to partially account for cisplatin resistance demonstrated by H2O2-resistant cells.

Effects of fatty acid oxidation on glucose utilization by isolated hepatocytes

We have studied the inhibitory action of long- and short-chain fatty acids on hepatic glucose utilization in hepatocytes isolated from fasted rats. The rates of hepatic glucose phosphorylation and glycolysis were determined from the tritiated products of [2-3H] and [6-3H]glucose metabolism, respectively. The difference between these was taken as an estimate of the 'cycling' between glucose and glucose-6-phosphate. In the presence of 40 mM glucose this cycling was estimated at 0.68 mumol/min/g wet wt. Glucose phosphorylation was unaffected during palmitate and hexanoate oxidation to ketone bodies but glycolysis was inhibited. The rate of glucose cycling was increased during this phase to 1.25 mumol/min/g. Following the complete metabolism of the fatty acids, glycolysis was reinstated and cycling rates returned to control levels. Hepatic glucose cycling appears to be an important component of the glucose/fatty acid cycle.

Noncomplementary DNA double-strand-break rejoining in bacterial and human cells

We examined the rejoining of noncomplementary restriction enzyme-produced DNA double-strand breaks in Escherichia coli and in cultured human cells. The enzymes used in this study, ClaI, BamHI and SalI, produce double-strand breaks with 5 protruding single strands. The joining of a ClaI-produced DNA end to a BamHI-produced end or to a SalI-produced end was examined at the DNA sequence level. End rejoining in E.coli was studied by transforming cultures with linear plasmid DNA that was gel purified from restriction digests, and end rejoining in cultured human cells was studied by introducing enzymes into the cells by electroporation. The human cells used contain an Epstein-Barr virus (EBV)-based shuttle vector, pHAZE, that was recovered and introduced into E.coli for further analysis. The major products of DNA end-joining processes observed in linear plasmid-transformed E.coli and in the human cells exposed to restriction enzymes were identical. Furthermore, the deletions observed in both systems and in the spontaneous mutant plasmids in untreated human cells had a common underlying feature: short stretches of directly repeated DNA at the junction sites.

Reducing-equivalent transfer to the mitochondria during gluconeogenesis and ureogenesis in hepatocytes from rats of different thyroid status

Isolated hepatocytes from hypothyroid, euthyroid and hyperthyroid rats have been employed to investigate the relative importance of reducing-equivalent shuttles for the transfer of hydrogen between cytoplasm and mitochondria during simultaneous ureogenesis and gluconeogenesis. In cells from hypothyroid animals, a 58% depression of glucose formation and 68% reduction in ureogenesis were induced by n-butylmalonate, an inhibitor of the malate shuttle. A more reduced state of the cytoplasmic compartment and a substantial fall in the concentrations of pyruvate, aspartate, alanine and glutamate accompanied this inhibition. Preincubation of cells with n-butylmalonate yielded greater inhibitory effects than observed in the absence of preincubation. The inhibitory effects on gluconeogenesis and ureogenesis were less in cells from euthyroid rats and were very much reduced in the case of glucose synthesis and absent in the case of ureogenesis, in cells from hyperthyroid rats. It is inferred that both the malate-aspartate and alpha-glycerophosphate shuttles may function in the transfer of reducing equivalents from cytoplasm to mitochondria during ureogenesis in hepatocytes. The major inhibition by n-butylmalonate of glucose and urea synthesis in hepatocytes from hypothyroid rats is due to the diminished activity of the alpha-glycerophosphate shuttle in these cells. Moreover, it follows that the NADH arising from the cytoplasmic malate dehydrogenase-catalysed reaction is accessible to both the malate-aspartate shuttle and the alpha-glycerophosphate shuttle.

The role of lipid peroxidation in McArdle's disease: applications for treatment of other myopathies

Experimental therapies for McArdle's disease have been directed toward increasing substrate availability to exercising muscle. Such therapies to date have proven largely unsuccessful. These include administration of isoproterenol to increase blood flow, glucagon treatment to elevate serum glucose and increased dietary fat intake. Each of these therapies also results in greater levels of unesterified fatty acids in blood. More recently, a high protein diet is suggested to provide increased amounts of amino acids which would be available as fuel sources. We hypothesize that the absence of myophosphorylase in McArdle's disease creates an imbalance between the enzymes of the redox systems that control the generation, propagation and inactivation of free radicals. This occurs because muscle cells are forced to rely more heavily on fatty acid oxidation. The resulting free radical damage to cellular components disrupts metabolic control and increases the permeability of membranes. Elevated levels of Ca2+ in the sarcoplasm activate proteases, phospholipases and other catabolic enzymes initiating muscle fatigue and cramping. Lipid peroxidation is a consequence of normal muscle activity and may occur unchecked in individuals with McArdle's disease. Continued muscle activity in the absence of a favorable nutritional environment may promote the progression of the disease by increasing susceptibility to oxidative stress.

Operation and energy dependence of the reducing-equivalent shuttles during lactate metabolism by isolated hepatocytes

The participation and energy dependence of the malate-aspartate shuttle in transporting reducing equivalents generated from cytoplasmic lactate oxidation was studied in isolated hepatocytes of fasted rats. Both lactate removal and glucose synthesis were inhibited by butylmalonate, aminooxyacetate or cycloserine confirming the involvement of malate and aspartate in the transfer of reducing equivalents from the cytoplasm to mitochondria. In the presence of ammonium ions the inhibition of lactate utilization by butylmalonate was considerably reduced, yet the transfer of reducing equivalents into the mitochondria was unaffected, indicating a substantially lesser role for butylmalonate-sensitive malate transport in reducing-equivalent transfer when ammonium ions were present. Ammonium ions had no stimulatory effect on uptake of sorbitol, a substrate whose oxidation principally involves the alpha-glycerophosphate shuttle. The role of cellular energy status (reflected in the mitochondrial membrane electrical potential (delta psi) and redox state), in lactate oxidation and operation of the malate-aspartate shuttle, was studied using a graded concentration range of valinomycin (0-100 nM). Lactate oxidation was strongly inhibited when delta psi fell from 130 to 105 mV whereas O2 consumption and pyruvate removal were only minimally affected over the valinomycin range, suggesting that the oxidation of lactate to pyruvate is an energy-dependent step of lactate metabolism. Our results confirm that the operation of the malate-aspartate shuttle is energy-dependent, driven by delta psi. In the presence of added ammonium ions the removal of lactate was much less impaired by valinomycin, suggesting an energy-independent utilization of lactate under these conditions. The oxidizing effect of ammonium ions on the mitochondrial matrix apparently alleviates the need for energy input for the transfer of reducing equivalents between the cytoplasm and mitochondria. It is concluded that, in the presence of ammonium ions, the transport of lactate hydrogen to the mitochondria is accomplished by malate transfer that is not linked to the electrogenic transport of glutamate across the inner membrane, and, hence, is clearly distinct from the butylmalonate-sensitive, energy-dependent, malate-aspartate shuttle.

Differential growth of brain and retinal bovine pericytes

Within the central nervous system, pericyte degeneration in diabetes mellitus occurs only in the retinal microcirculation and is not seen in the brain. This study sought to elucidate differences between bovine retinal and brain pericytes. When pairs of retinal and brain pericytes from individual calves were cultured in vitro, the morphological organisation of early post-confluent retinal pericyte cultures was consistently different from that of brain pericyte cultures. When retinal and brain pericyte cultures were grown to second passage in high or normal glucose medium supplemented with fetal calf serum, brain pericyte cultures grew significantly faster than retinal pericytes in either medium (p less than 0.0001). Brain pericytes thus appeared to grow intrinsically faster than retinal pericytes and this effect was largely independent of glucose concentration. Brain pericytes also grew faster than retinal pericytes in high glucose medium containing human diabetic or control serum (p less than 0.002). The proliferative effect of serum from diabetic patients with non-proliferative diabetic retinopathy on pericytes grown in high glucose medium was not significantly different from that of control serum. Both brain and retinal pericytes showed variation in their ability to replicate in high concentrations of glucose. The selectivity of pericyte degeneration to the retinal circulation does not appear to be due to changes in the mitogenic activity of diabetic serum for retinal pericytes, but may relate to the intrinsic relative inability of the retinal pericyte to reproliferate in response to the metabolic injury of diabetes mellitus.

Evaluation of support bandaging during measurement of proximal sesamoidean ligament strain in horses by use of a mercury strain gauge

Liquid mercury strain gauges were implanted in the forelimb proximal sesamoidean ligaments (PSL) of 8 adult horses. The gauges measured PSL strain while horses were standing with or without external support. In 6 of the horses, the gauges also measured PSL strain in horses at a walk, with or without external support. Gauges were enclosed within sliding polypropylene tubes to prevent nonaxial deformation. Each gauge was placed in 1 arm of a low-resistance half-bridge circuit. To provide temperature compensation, a dummy gauge was placed in the adjacent arm of the bridge circuit and was implanted next to the active gauge in the surrounding fascial tissue. External support included fiberglass cast support (CAST), dorsal fetlock splint support (DFS), support wraps of 3 bandage materials (SW1, SW2, and SW3), and support wrap with caudal splint (SW4). The cast was applied, with the fetlock and foot in weightbearing position, from the proximal portion of the metacarpus distal to and including the foot. The DFS was applied by placing the cranial half of the fiberglass cast on the dorsal aspect of the instrumented limb. The SW1, SW2, and SW3 were applied in a figure-8 pattern around the fetlock, using 50% of the linear stretch capacity of the bandage material, with the horse standing squarely on all 4 limbs. The SW4 was applied identically to the other support wraps, with the exception of addition of a flexible caudal splint incorporated in the support wrap. Mean maximal strain while standing (epsilon S) without external support for 8 horses was 6.0% (range, 3.8 to 7.5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between mitochondria and cytoplasm in isolated hepatocytes

Results from a wide variety of metabolic studies have provided indirect support for conclusions derived from enzymological approaches that the enzymes of the so-called soluble cytoplasm (and the mitochondrial matrix) exist within the cell and function in the form of multienzyme complexes and that metabolite channeling takes place between the enzymes of each complex. Our studies support the possibility that the enzymes of glycolysis in liver are segregated from those of gluconeogenesis. Thus, the segregation and aggregation of Krebs cycle enzymes in the mitochondrial matrix, elucidated by Paul Srere, may be an example of a general pattern of enzyme organization pertaining to all metabolic pathways.

Analysis of restriction enzyme-induced DNA double-strand breaks in Chinese hamster ovary cells by pulsed-field gel electrophoresis: implications for chromosome damage

Restriction enzymes can be electroporated into mammalian cells, and the induced DNA double-strand breaks can lead to aberrations in metaphase chromosomes. Chinese hamster ovary cells were electroporated with PstI, which generates 3' cohesive-end breaks, PvuII, which generates blunt-end breaks, or XbaI, which generates 5' cohesive-end breaks. Although all three restriction enzymes induced similar numbers of aberrant metaphase cells, PvuII was dramatically more effective at inducing both exchange-type and deletion-type chromosome aberrations. Our cytogenetic studies also indicated that enzymes are active within cells for only a short time. We used pulsed-field gel electrophoresis to investigate (i) how long it takes for enzymes to cleave DNA after electroporation into cells, (ii) how long enzymes are active in the cells, and (iii) how the DNA double-strand breaks induced are related to the aberrations observed in metaphase chromosomes. At the same concentrations used in the cytogenetic studies, all enzymes were active within 10 min of electroporation. PstI and PvuII showed a distinct peak in break formation at 20 min, whereas XbaI showed a gradual increase in break frequency over time. Another increase in the number of breaks observed with all three enzymes at 2 and 3 h after electroporation was probably due to nonspecific DNA degradation in a subpopulation of enzyme-damaged cells that lysed after enzyme exposure. Break frequency and chromosome aberration frequency were inversely related: The blunt-end cutter PvuII gave rise to the most aberrations but the fewest breaks, suggesting that it is the type of break rather than the break frequency that is important for chromosome aberration formation.

Chromosomal aberration induction in CHO cells by combined exposure to restriction enzymes and X-rays

The potential interaction between restriction enzyme-induced double-strand breaks (dsb) and X-ray-induced lesions in the formation of chromosomal aberrations was investigated in Chinese hamster ovary cells. Either Alu I, which induces blunt-end dsb, or Sau 3AI, which induces cohesive-end dsb, was electroporated into cells, which were irradiated with 2 Gy of X-rays immediately or 15, 30, 60, 120, or 180 min after electroporation. A significant increase in Alu I-induced chromosomal aberrations was observed when cells were irradiated with 0, 15, 30, or 60 min after enzyme exposure, but only additive effects were found when cells were irradiated 120 or 180 min after enzyme exposure. In one of three experiments, cells exposed to Sau 3AI showed a large increase in aberrations when X-irradiated 0 or 15 min after Sau 3AI exposure, and no increase at any time-points thereafter. These results indicate that restriction enzyme-induced dsb can interact with X-ray-induced lesions, resulting in a synergistic increase in chromosomal aberration formation. Furthermore, this interaction depends on both the type of dsb and the time between enzyme and X-ray exposure.

Modulation of restriction enzyme-induced damage by chemicals that interfere with cellular responses to DNA damage: a cytogenetic and pulsed-field gel analysis

The electroporation of restriction enzymes into mammalian cells results in DNA double-strand breaks that can lead to chromosome aberrations. Four chemicals known to interfere with cellular responses to DNA damage were investigated for their effects on chromosome aberrations induced by AluI and Sau3AI; in addition, the number of DNA double-strand breaks at various times after enzyme treatment was determined by pulsed-field gel electrophoresis (PFGE). The poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide (3AB) dramatically increased the yield of exchanges and deletions and caused a small but transitory increase in the yield of double-strand breaks induced by the enzymes. 1-beta-D-Arabinofuranosylcytosine, which can inhibit DNA repair either by direct action on DNA polymerases alpha and delta or by incorporation into DNA, potentiated aberration induction but to a lesser extent than 3AB and did not affect the amount of DNA double-strand breakage. Aphidicolin, which inhibits polymerases alpha and delta, had no effect on AluI-induced aberrations but did increase the aberration yield induced by Sau3AI. The postreplication repair inhibitor caffeine had no effect on aberration yields induced by either enzyme. Neither aphidicolin nor caffeine modulated the amount of DNA double-strand breakage as measured by PFGE. These data implicate poly(ADP-ribosyl)ation and polymerases alpha and delta as important components of the cellular processes required for the normal repair of DNA double-strand breaks with blunt or cohesive ends. Comparison of these data with the effect of inhibitors on the frequency of X-ray-induced aberrations leads us to the conclusion that X-ray-induced aberrations can result from the misjoining or nonrejoining of double-strand breaks, particularly breaks with cohesive ends, but that this process accounts for only a portion of the induced aberrations.

Chromosome aberration induction in Chinese hamster ovary cells by restriction enzymes with different methylation sensitivity

The isoschizomer pair MspI and HpaII were used to investigate whether the putative specificity of restriction endonucleases would be maintained when they were introduced into mammalian cells. Although both enzymes recognize the sequence CCGG, HpaII will cut only if the internal cytosine is unmethylated, whereas MspI will cut regardless of the methylation status. Cleavage results in a cohesive-end DNA double-strand break, which can lead to the formation of chromosome aberrations. Since mammalian DNA is heavily methylated, one would expect MspI to be much more effective than HpaII at inducing chromosome aberrations in Chinese hamster ovary cells. In fact, during G1, MspI induced a greater than 90-fold higher number of aberrations than did HpaII. Cell cycle studies indicated that during early S there was a 30-fold increase in HpaII-induced aberrations. This increase may be due to increased accessibility of replicating hypomethylated DNA. Cells that were treated with the demethylating agent 5-aza-2'-deoxycytidine (AzdC) displayed only a moderate increase in HpaII-induced aberrations during G1. This observation, together with the results of restriction enzyme analysis of genomic DNA, indicated that demethylation was incomplete. The effects of AzdC on the induction of aberrations by MspI suggested that AzdC increases chromatin accessibility. Our results were consistent with the expected specificity of MspI and HpaII. Thus, it appears that restriction endonucleases can play a useful role in determining the biological consequences of DNA double-strand breaks.

Bahia grass pollen, a significant aeroallergen: evidence for the lack of clinical cross-reactivity with timothy grass pollen

Thirty-eight subjects were challenged (25 nasal, 13 bronchial) with Bahia grass, Paspalum notatum, pollen extract. A positive Bahia intradermal skin test predicted a positive challenge to Bahia in all (11/11) of the nasal challenges and 75% (6/8) of the bronchial challenges. All 19 subjects with negative Bahia intradermal skin tests had negative challenges with Bahia. Specific IgE antibodies to Bahia pollen were detected by conventional RAST (greater than or equal to 2+) in 82% (14/17) of subjects with positive challenges and in 5% (1/20) of subjects with negative challenges. Eight subjects had positive intradermal skin tests to either Bahia (three) or timothy, Phleum pratense (five). Seven of the eight subjects reacted exclusively to either Bahia or timothy nasal challenge as predicted by their skin tests. Bahia grass is a significant aeroallergen, which in some subjects can be demonstrated not to cross-react with timothy.

Restriction endonucleases do not induce sister-chromatid exchanges in Chinese hamster ovary cells

Bacterial restriction enzymes offer the unique opportunity to determine the biological and cytogenetic consequences of DNA double-strand breakage. To examine the role of various types of breaks in sister-chromatid exchange (SCE) formation, we used restriction enzymes with different recognition sequences and different cutting frequencies to generate DNA double-strand breaks in Chinese hamster ovary (CHO) cells. The restriction enzymes were introduced by electroporation into exponentially growing cells during the second replication cycle in bromodeoxyuridine, and SCEs were analyzed at mitosis. Contrary to results reported by others, we found no increase in SCE frequency in cells exposed to restriction enzymes despite the presence of numerous cells with chromatid aberrations. These data suggest that DNA double-strand breaks do not lead to SCE formation.

Obstruction of the small bowel in the early postoperative period

To analyze factors related to etiology, diagnosis, and outcome, we reviewed the records of 26 patients in whom a clinical picture of small bowel obstruction developed within one month after abdominal surgery. The initial operation was an emergency procedure in 20 cases and an exploratory laparotomy after trauma in 11. The colon was the organ most commonly operated upon initially, being involved in ten procedures (38%), all of which were emergencies. The clinical diagnosis of bowel obstruction was made within ten days postoperatively in most cases. Surgical reexploration was required in 15 patients (58%), whereas the obstructive symptoms resolved with nasogastric suction in 11. Two patients, both of whom survived, required resection of strangulated bowel; in both a treatment delay of at least 72 hours was documented. There were two deaths (8%), neither of which was directly related to the bowel obstruction. Diagnosis of this clinical entity requires a high index of suspicion, especially after emergency procedures that involve the colon. Optimal survival is achieved by prompt recognition and early intervention when a mechanical bowel obstruction is suspected in the early postoperative period.

Cell electroporation is a highly efficient method for introducing restriction endonucleases into cells

Restriction endonucleases that make either blunt- or cohesive-end DNA double-strand breaks can induce chromosome aberrations. We have used cell electroporation with great success to permeabilize Chinese hamster ovary cells for the introduction of restriction enzymes. The introduction of restriction enzymes by this method resulted in extremely high frequencies (greater than 90%) of aberrant metaphase cells and also a dramatic decrease in cell survival, as measured by subsequent colony formation. Cell electroporation by itself caused no increase in aberrant chromosomes and had only a slight effect on cell survival.

Intracellular mitochondrial membrane potential as an indicator of hepatocyte energy metabolism: further evidence for thermodynamic control of metabolism

The lipophilic triphenylmethylphosphonium cation (TPMP+) has been employed to measure delta psi m, the electrical potential across the inner membrane of the mitochondria of intact hepatocytes. The present studies have examined the validity of this technique in hepatocytes exposed to graded concentrations of inhibitors of mitochondrial energy transduction. Under these conditions, TPMP+ uptake allows a reliable measure of delta psi m in intracellular mitochondria, provided that the ratio [TPMP+]i/[TPMP+]e is greater than 50:1 and that at the end of the incubation more than 80% of the hepatocytes exclude Trypan blue. Hepatocytes, staining with Trypan blue, incubated in the presence of Ca2+, do not concentrate TPMP+. The relationships between delta psi m and two other indicators of cellular energy state, delta GPc and Eh, or between delta psi m and J0, were examined in hepatocytes from fasted rats by titration with graded concentrations of inhibitors of mitochondrial energy transduction. Linear relationships were generally observed between delta psi m and delta GPc, Eh or J0 over the delta psi m range of 120-160 mV, except in the presence of carboxyatractyloside or oligomycin, where delta psi m remained constant. Both the magnitude and the direction of the slope of the observed relationships depended upon the nature of the inhibitor. Hepatocytes from fasted rats synthesized glucose from lactate or fructose, and urea from ammonia, at rates which were generally linear functions of the magnitude of delta psi m, except in the presence of oligomycin or carboxyatractyloside. Linear relationships were also observed between delta psi m and the rate of formation of lactate in cells incubated with fructose and in hepatocytes from fed rats. The linear property of these force-flow relationships is taken as evidence for the operation of thermodynamic regulatory mechanisms within hepatocytes.

The effects of screw removal on bone strain in an idealized plated bone model

An idealized plated bone model was used to test the hypothesis that selected screw removal could alter the bone strain field and be a viable treatment for stress protection osteoporosis. Eighteen bone screw modifications were evaluated for their effects on bone strain. The three variables studied were number, position, and length of screws. Removal of two or four bone screws from an eight hole plate significantly increased the strain per load on the bone model over the values with eight screws in the plate (p less than 0.05). The four screw configurations increased bone strain more than the six screw configurations. It also was shown that the position of screws in the plate could significantly alter the bone strain per load results. Removal of six bone screws from an eight hole plate also increased the bone strain per load, but to excess in some tests. In those configurations, the results were not statistically different from the unplated configuration. Replacement of the full length screws with eight half length screws that engaged only the near cortex significantly reduced bone strain per load as compared with eight bicortical bone screws.

Evidence that stimulation of gluconeogenesis by fatty acid is mediated through thermodynamic mechanisms

We have studied the stimulatory effects of palmitate on the rate of glucose synthesis from lactate in isolated hepatocytes. Control of the metabolic flow was achieved by modulating the activity of enolase using graded concentrations of fluoride. Unexpectedly, palmitate stimulated gluconeogenesis even when enolase was rate-limiting. This stimulation was also observed when the activities of phosphoenolpyruvate carboxykinase and aspartate aminotransferase were modulated using graded concentrations of quinolinate and aminooxyacetate, respectively. Linear force-flow relationships were found between the rate of gluconeogenesis and indicators of cellular energy status (i.e. mitochondrial membrane and redox potentials and cellular phosphorylation potential). These findings suggest that the fatty acid stimulation of glucose synthesis is in part mediated through thermodynamic mechanisms.

Linear relationships between mitochondrial forces and cytoplasmic flows argue for the organized energy-coupled nature of cellular metabolism

We have studied rates of formation of glucose, urea and lactate by isolated hepatocytes incubated with a variety of inhibitors of energy transduction. Linear relationships have been found between these metabolic rates and mitochondrial forces (membrane, redox and phosphorylation potentials). The findings are suggestive of extensive enzyme organization within these metabolic pathways.

Preparation of cytoplasmic bodies (cytospheres) from isolated hepatocytes and their biochemical properties

The controlled centrifugation of isolated rat hepatocytes at 260 000 g results in the formation of membrane-bounded cell fragments that we have termed 'cytospheres'. A method is described for the isolation of these cytospheres. Cytospheres are spherical, have a mean diameter of 9.2 +/- 3.2 microns (SD) and a protein content of 225 +/- 12 mg/g wet wt. About 3% of the protein from the original isolated hepatocyte suspension is recoverable. Transmission electron microscopy (TEM) shows cytospheres to possess a trilaminar membrane, and a finely granular hyaloplasm generally devoid of organelles, filaments and microtubules. Freeze-fracture studies reveal a membrane structure typical of a plasma membrane. Ouabain and wheat germ agglutinin (WGA)-binding studies indicate that the original orientation of the plasma membrane is maintained throughout the formation of the cytospheres. The cytospheres have also been characterized biochemically. Cytospheres are enriched in the enzymes normally associated with the hyaloplasm, whereas the activities of enzymes localized in organelles are greatly diminished. Lipid analysis of the cytosphere membrane indicates that it is derived from the plasma membrane of the hepatocyte. Cytospheres are sensitive to changes in the osmolarity and ionic composition of their environment. Cytospheres should therefore prove a useful preparation for the study of hyaloplasm metabolism and of plasma membrane receptor and permeability properties.

Some unexplained features of hepatic ethanol oxidation

Ethanol is an excellent substrate for the liver, competing effectively for oxidation with other substrates such as fatty acids. Using isolated liver cells from fed and starved rats, we have found that ethanol strongly inhibits Krebs cycle oxidations, so that the combustion through the cycle of acetyl CoA, derived from fatty acids, is reduced more than 50%. In contrast, fatty acid beta-oxidation to acetyl CoA is inhibited only 20% in fed and fasted states. Ethanol was not antiketogenic. In the fed state, octanoate but not palmitate inhibited ethanol oxidation whereas in cells from fasted rats palmitate inhibited ethanol oxidation. Gluconeogenesis from lactate was reduced 50% in hepatocytes from fasted rats but oxygen consumption was unaffected. This paradoxical maintenance of oxygen consumption in a state where the only overt need for ATP synthesis is depressed, suggests that ethanol oxidation may not be exclusively coupled to ATP synthesis but also can be linked to other energy transducing processes.