[Lectin-binding histochemical study on developing corneal epithelium and stroma of normal human being]

PURPOSE

To study glycoconjugates in developing cornea of normal human.

METHODS

Lectin-binding histochemical method with five biotin-coupled lectins (conA, LCA, PNA, WGA, RCA).

RESULTS

1. WGA mainly stained the membrane of epithelial cells, especially in surface cells. It also stained anterior stroma of embryo. 2. All the layers of epithelium could be stained by conA, uneven stain was seen in stroma of embryo corneas. 3. RCA, LCA receptor distributed in base of cornea epithelium. 4. PNA can only stain cornea epithelium of 16 embryo.

CONCLUSIONS

1. Glycoconjugates of binding conA, WGA, PNA, LCA, RCA are in the developing corneas of human. 2. The distribution of these lectin receptors may change with corneal developing. It may be related to the maturity of corneas.

Cleavage of RNA hairpins mediated by a developmentally regulated CCCH zinc finger protein

Control of RNA turnover is a major, but poorly understood, aspect of gene regulation. In multicellular organisms, progress toward dissecting RNA turnover pathways has been made by defining some cis-acting sequences that function as either regulatory or cleavage targets (J. G. Belasco and G. Brawerman, Control of Messenger RNA Stability, 1993). However, the identification of genes encoding proteins that regulate or cleave target RNAs has been elusive (C. A. Beelman and R. Parker, Cell 81:79-183, 1995); this gap in knowledge has made it difficult to identify additional components of RNA turnover pathways. We have utilized a modified expression cloning strategy to identify a developmentally regulated gene from Drosophila melanogaster that encodes a RNase that we refer to as Clipper (CLP). Significant sequence matches to open reading frames encoding unknown functions identified from the Caenorhabditis elegans and Saccharomyces cerevisiae genome sequencing projects suggest that all three proteins are members of a new protein family conserved from lower eukaryotes to invertebrates. We demonstrate that a member of this new protein family specifically cleaves RNA hairpins and that this activity resides in a region containing five copies of a previously uncharacterized CCCH zinc finger motif. CLP's endoribonucleolytic activity is distinct from that associated with RNase A (P. Blackburn and S. Moore, p. 317-433, in P. D. Boyer, ed., The Enzymes, vol. XV, part B, 1982) and is unrelated to RNase III processing of rRNAs and tRNAs (J. G. Belasco and G. Brawerman, Control of Messenger RNA Stability, 1993, and S. A. Elela, H. Igel, and M. Ares, Cell 85:115-124, 1995). Our results suggest that CLP may function directly in RNA metabolism.

GSH transport and GSH-dependent detoxication in small intestine of rats exposed in vivo to hypoxia

The effects of hypoxia on glutathione (GSH) concentration and GSH-related enzyme and transport systems were studied in the small intestine of rats exposed to 8-10 days of 10.5% O2. Exposure to hypoxia resulted in a 40% lower GSH concentration in enterocytes and a 50% lower concentration in blood plasma. Activities of GSH-related detoxication enzymes in the intestinal epithelium were largely unaffected by hypoxic exposure. GSH degradation and synthesis rates in enterocytes isolated from hypoxic rats were comparable with rates in normoxic controls, but GSH uptake rate was decreased by 30%. Stimulation of absorption of GSH by phenylephrine, such as occurs in control rats, was not detectable in isolated, vascularly perfused intestines of hypoxic rats. Decreased GSH uptake was associated with enhanced transepithelial appearance of thiobarbituric acid-reactive substances in everted intestinal sacs incubated with peroxidized methyl linoleate. These results suggest that chronic hypoxia results in impaired uptake of GSH in the small intestine, and this may result in impaired GSH-related defense mechanisms in the small intestine.

SKP1 connects cell cycle regulators to the ubiquitin proteolysis machinery through a novel motif, the F-box

We have identified the yeast and human homologs of the SKP1 gene as a suppressor of cdc4 mutants and as a cyclin F-binding protein. Skp1p indirectly binds cyclin A/Cdk2 through Skp2p, and directly binds Skp2p, cyclin F, and Cdc4p through a novel structural motif called the F-box. SKP1 is required for ubiquitin-mediated proteolysis of Cin2p, Clb5p, and the Cdk inhibitor Sic1p, and provides a link between these molecules and the proteolysis machinery. A large number of proteins contain the F-box motif and are thereby implicated in the ubiquitin pathway. Different skp1 mutants arrest cells in either G1 or G2, suggesting a connection between regulation of proteolysis in different stages of the cycle.

Insulin receptor mediates inhibitory effect of insulin, but not of insulin-like growth factor (IGF)-I, on IGF binding protein 1 (IGFBP-1) production in human granulosa cells

Insulin-like growth factor binding proteins (IGFBPs) may participate in regulating ovarian function by modifying effects of insulin-like growth factors (IGFs) or by directly affecting ovarian steroidogenesis in both normal and pathological circumstances. The latter include hyperinsulinemic insulin resistant states, such as polycystic ovary syndrome. We examined regulation of IGFBP-1 production in human granulosa cells by insulin and IGF-I. The cells were obtained during in vitro fertilization, plated in McCoy-5A tissue culture medium supplemented with 10% fetal calf serum (10(5) cells/0.5 mL), and incubated at 37 C, 90% humidity, 5% CO2 for 48 h. After additional 24 h incubation without fetal calf serum, 1, 10, or 100 ng/mL of insulin or IGF-I were added with or without 2 h preincubation with 10 micrograms/mL monoclonal anti insulin receptor antibody IR-47-9. After 48 h incubation with insulin or IGF-I, the medium was collected and IGFBP-1 and progesterone concentrations were measured, using kits from Diagnostic Systems Laboratories, Webster, TX. Progesterone concentration ranged between 50-100 ng/mL/10(5) cells, without consistent stimulatory effect of either insulin or IGF-I. Control cells produced 7.0 +/- 1.7 ng/mL of IGFBP-1. Incubation with 1 or 10 ng/mL of insulin resulted in culture medium IGFBP-1 concentrations of 7.1 +/- 1.3 ng/mL and 5.4 +/- 0.7 ng/mL, respectively (P = NS). Incubation with 100 ng/mL of insulin reduced IGFBP-1 culture medium concentration to 1.6 +/- 0.3 ng/mL (P < 0.01, compared with controls). 1, 10, and 100 ng/mL of IGF-I inhibited IGFBP-1 concentrations in the conditioned culture medium to 1.3 +/- 0.3 ng/mL, 0.4 +/- 0.1 ng/mL and 0.3 +/- 0.1 ng/mL, respectively (P < 0.01, compared with controls). Preincubation with antiinsulin receptor antibody IR-47-9 alleviated inhibitory effect of insulin, but not of IGF-I on IGFBP-1 production. After preincubation with IR-47-9, IGFBP-1 culture medium concentrations were 5.9 +/- 0.8 ng/mL, 4.9 +/- 1.2 ng/mL, and 4.8 +/- 1.3 ng/mL for 1, 10, and 100 ng/mL of insulin, respectively. The latter number was significantly higher than IGFBP-1 concentration in the medium collected from cells incubated with 100 ng/mL of insulin without IR-47-9 (1.6 +/- 0.3 ng/mL, P < 0.01) and not significantly different from the control cells. For cells preincubated with IR-47-9 and then incubated with 1, 10, or 100 ng/mL of IGF-I, the IGFBP-1 conditioned culture medium concentrations were 1.7 +/- 0.1 ng/mL, 0.5 +/- 0.2 ng/mL, and 0.3 +/- 0.1 ng/mL, respectively. None of these were significantly different from the IGFBP-1 concentrations in the medium collected from cells incubated with the respective concentrations of IGF-I without preincubation with IR-47-9. We conclude that 1) both insulin and IGF-I inhibit IGFBP-1 production by cultured human granulosa cells; 2) IGF-I is a more potent inhibitor of IGFBP-1 production than insulin; 3) in the range of hormone concentrations tested, insulin exerts its inhibitory effect on IGFBP-1 production via insulin receptor, while IGF-I appears to exert its effect via another receptor.

Atomic force microscopic study on topological structures of pBR322 DNA

Plasmid pBR322 DNA (0.5 mg/mL) isolated from Escherichia coli HB101 was suspended in Tris-HCI-EDTA (1 mol/L-0.1 mol/L, pH 8.5); then a drop of the above solution was deposited on freshly cleaved mica substrate. After adsorption for about 1 mm, the sample was stained with phosphotungstic acid. The residual solution was removed with a piece of filter paper. Afterwards the sample was imaged with a home-made atomic force microscope (AFM) in air. The AFM images of pBR322 DNA with a molecular resolution have been obtained. These images show that pBR322 DNA exists in several different topological structures: (i) relaxed circular DNA with a different diameter; (ii) supercondensed DNA with different particle sizes; (iii) dimeric catenane connected by one relaxed circular molecule and another close-compacted molecule which might be either supercoiled or intramolecular knotted form; (iv) oligomeric catenane with multiple irregular molecules in which DNA is interlocked into a complex oligomer; (v) possibly-existing intermediates formed from monomer to oligomer.

Effect of selective cytosine methylation and hydration on the conformations of DNA triple helices containing a TTTT loop structure by FT-IR spectroscopy

5-Methylcytosines have been introduced into triplex-forming-oligonucleotides and shown to extend the pH range over which a triplex forms with a homopurine-homopyrimidine tract of duplex DNA. As a host strand, an oligodeoxypyrimidine with a base sequence of 5'-d(TC)3T4(CT)3 ([CC]) was designed to form a hairpin triplex with a 5'-d-A(GA)2G ([AG6]) purine strand at acidic pH (Tsay, et al., (1995) J. Biomol. Str. Dyn., 13, 1235-1245). We here present results obtained by FT-IR spectroscopy concerning the conformation of the hairpin triplex as a function of the selective substitution of cytosines by 5-methylcytosines in the host strand. Namely, cytosines are substituted by 5-methylcytosines in either the 3'-pyrimidine portion ([CM]) or the 5'-pyrimidine portion ([MC]) or in both ([MM]) of the host strand. The acidic-induced transitions of the equimolar mixtures of the purine target with either of the four pyrimidine oligomers gives rise to different apparent pK values, i.e., [MM].[AG6] (6.2) > [MC].[AG6] (6.0) > [CM].[AG6] (5.7) > [CC].[AG6] (5.2) > single-stranded oligopyrimidines (4.6 +/- 0.2), indicating that cytosine methylation expands the pH range compatible with the hairpin triplex formation regardless of whether the substitution is in the 5'-pyrimidine (Hoogsteen) portion or in the 3'-pyrimidine (Watson-Crick) portion. Thermal denaturation profiles indicated that all the triplexes denatured in a monophasic manner in the pH range of 4.0 to 7.0, and that cytosine methylations in any position of the 16-base pyrimidine oligomer increase the stability of the hairpin triplex DNA. IR spectra recorded in D2O and H2O solutions revealed that cytosine methylation does not significantly influence the conformation of triplex DNA in solution, i.e., all the four triplexes accept a similar sugar conformation, and predominately take on a S-type sugar pucker with a relative proportion of two S-type sugars for one N-type. Furthermore, we also investigated the effect of relative humidity (RH) on the conformation of triplex MC.AG6 in hydrated films, and found that the conformational change induced by the decrease of RH, from predominant S-type to primary N-type sugar pucker, might first occur in the purine strand at 86% RH.

Laser Raman spectrometry study on experimental galactose-induced cataract

PURPOSE

To observe the dynamic changes of hydration in galactose induced cataract.

METHODS

Two groups of Wistar rats were used in the experiment. There were 12 rats in the experimental group, which were fed diet of 50% D-Galactose standard feed; while the control group had 8 rats fed standard feed. Their other living conditions were the same. At desired time periods, two Wistar rats fed galactose and one normal control were selected and killed 20 minutes before the instrument examination respectively, then, their lenses were removed from the orbs by a posterior approach. The cleaned fresh lens was placed in a quartz cuvette with Tris buffered balanced salt solution containing 5.5 mmol/L glucose. The quartz cuvette was placed on the stage of the Spectrometer. The laser beam was focused at the lens nuclear from the bottom of the cuvette and the scattered light was collected at 90 degrees to the incident beam.

RESULTS

Raman spectroscopy showed that (1) during the formation of galactose cataract, the water signal (at 3390cm-1) increased obviously, and the ratio of I3390/I2935 increased from 0.31 (3 days) to 2.26 (17 days), which is correlated with the imbibition of water in the lens nuclear; (2) the hydration of lens nuclear could be divided into two phases. The ratio I3390/I2935 was increased slowly and steadily by 11 days after galactose feeding. Then, the ratio turned to increase quite fast till 17 days.

CONCLUSION

The hydration of nuclear is changed simultaneously with the formation of cataract. The hydration of nuclear is mainly due to the imbalance of Na+/K+.

Inhibition of cyclin-dependent kinases by p21

p21Cip1 is a cyclin-dependent kinase (Cdk) inhibitor that is transcriptionally activated by p53 in response to DNA damage. We have explored the interaction of p21 with the currently known Cdks. p21 effectively inhibits Cdk2, Cdk3, Cdk4, and Cdk6 kinases (Ki 0.5-15 nM) but is much less effective toward Cdc2/cyclin B (Ki approximately 400 nM) and Cdk5/p35 (Ki > 2 microM), and does not associate with Cdk7/cyclin H. Overexpression of P21 arrests cells in G1. Thus, p21 is not a universal inhibitor of Cdks but displays selectivity for G1/S Cdk/cyclin complexes. Association of p21 with Cdks is greatly enhanced by cyclin binding. This property is shared by the structurally related inhibitor p27, suggesting a common biochemical mechanism for inhibition. With respect to Cdk2 and Cdk4 complexes, p27 shares the inhibitory potency of p21 but has slightly different kinase specificities. In normal diploid fibroblasts, the vast majority of active Cdk2 is associated with p21, but this active kinase can be fully inhibited by addition of exogenous p21. Reconstruction experiments using purified components indicate that multiple molecules of p21 can associate with Cdk/cyclin complexes and inactive complexes contain more than one molecule of p21. Together, these data suggest a model whereby p21 functions as an inhibitory buffer whose levels determine the threshold kinase activity required for cell cycle progression.

p57KIP2, a structurally distinct member of the p21CIP1 Cdk inhibitor family, is a candidate tumor suppressor gene

Cyclin-dependent kinases (Cdks) are positive regulators of cell proliferation, whereas Cdk inhibitors (CKIs) inhibit proliferation. We describe a new CKI, p57KIP2, which is related to p21CIP1 and p27KIP1. p57KIP2 is a potent, tight-binding inhibitor of several G1 cyclin/Cdk complexes, and its binding is cyclin dependent. Unlike CIP1, KIP2 is not regulated by p53. Overexpression of p57KIP2 arrests cells in G1. p57KIP2 proteins have a complex structure. Mouse p57KIP2 consists of four structurally distinct domains: an amino-terminal Cdk inhibitory domain, a proline-rich domain, an acidic-repeat region, and a carboxy-terminal domain conserved with p27KIP1. Human p57KIP2 appears to have conserved the amino- and carboxy-terminal domains but has replaced the internal regions with sequences containing proline-alanine repeats. In situ hybridization during mouse embryogenesis revealed that KIP2 mRNA displays a striking pattern of expression during development, showing high level expression in skeletal muscle, brain, heart, lungs, and eye. Most of the KIP2-expressing cells are terminally differentiated, suggesting that p57KIP2 is involved in decisions to exit the cell cycle during development and differentiation. Human KIP2 is located at 11p15.5, a region implicated in both sporadic cancers and Beckwith-Wiedemann syndrome, a familial cancer syndrome, marking it as a candidate tumor suppressor. The discovery of a new member of the p21CIP1 inhibitor family with novel structural features and expression patterns suggests a complex role for these proteins in cell cycle control and development.

Isolation, identification, and synthesis of Mas-MG-MT I, a novel peptide from the larval midgut of Manduca sexta (Lepidoptera: Sphingidae)

A five-residue myotropic peptide, Manduca sexta midgut myotropin I (Mas-MG-MT I), was isolated from an extract of 800 midguts of fifth instar larvae of the tobacco hornworm, Manduca sexta. It was purified by reverse phase and normal phase HPLC. Myotropic activity was screened by a heterologous Locusta migratoria oviduct bioassay. Sequence analysis, amino acid composition analysis, and comparison of candidate synthetic peptides in the amide and acid form revealed the following primary structure: Ala-Glu-Pro-Tyr-Thr-NH2. This is the first fully identified peptide isolated directly from the midgut of an insect species. Few significant sequence homologies with known vertebrate and invertebrate peptides have been found.

Human cyclin F

Cyclins are important regulators of cell cycle transitions through their ability to bind and activate cyclin-dependent protein kinases. In mammals several classes of cyclins exist which are thought to co-ordinate the timing of different events necessary for cell cycle progression. Here we describe the identification of a novel human cyclin, cyclin F, isolated as a suppressor of the G1/S deficiency of a Saccharomyces cerevisiae cdc4 mutant. Cyclin F is the largest cyclin, with a molecular weight of 87 kDa, and migrates as a 100-110 kDa protein. It contains an extensive PEST-rich C-terminus and a cyclin box region that is most closely related to cyclins A and B. Cyclin F mRNA is ubiquitiously expressed in human tissues. It fluctuates dramatically through the cell cycle, peaking in G2 like cyclin A and decreasing prior to decline of cyclin B mRNA. Cyclin F protein accumulates in interphase and is destroyed at mitosis at a time distinct from cyclin B. Cyclin F shows regulated subcellular localization, being localized in the nucleus in most cells, with a significant percentage of cells displaying only perinuclear staining. Overexpression of cyclin F, or a mutant lacking the PEST region, in human cells resulted in a significant increase in the G2 population, implicating cyclin F in the regulation of cell cycle transitions. The ubiquitous expression and phylogentic conservation of cyclin F suggests that it is likely to coordinate essential cell cycle events distinct from those regulated by other cyclins.

Glutathione transport by type II cells in perfused rat lung

Glutathione (GSH) is an antioxidant that protects the lung against oxidative-injury. Most cells rely on synthesis of GSH to maintain intracellular supply and only a few cell types take up intact GSH. Although isolated type II cells from rat have a Na(+)-dependent uptake system that transports GSH into the cells against a concentration gradient, it is not known whether this occurs from the vasculature in the intact lung or whether other cell types in the lung also transport GSH. Based on the knowledge that gamma-glutamyl analogues of GSH are also transported by the Na(+)-GSH transporter, a method was developed and used to study the cell specificity of GSH uptake in perfused lung. A stable, fluorescent GSH S-conjugate (GSH-I14) was synthesized and separated from the original dye as analyzed by high-performance liquid chromatography. Studies with isolated alveolar type II cells showed that uptake of GSH-I14 was Na+ dependent and inhibited by GSH. In addition, uptake of GSH by the type II cells was inhibited by GSH-I14. After perfusion of the isolated rat lung with GSH-I14, the conjugate accumulated primarily in the alveolar type II cell as observed by fluorescence microscopy. This was confirmed by isolation of type II cells and measurement of GSH-I14 content. Thus these results show that specificity of GSH transport can be studied with the fluorescent derivative, GSH-I14, and that in the isolated perfused lung type II cells can transport and concentrate GSH-I14 from the perfusate. Quantitative fluorescence microscopy will be required to further determine relative transport activities by other cell types.

Developmental characterization of a Drosophila RNA-binding protein homologous to the human systemic lupus erythematosus-associated La/SS-B autoantigen

Patients with humoral autoimmune diseases such as systemic lupus erythematosus and Sjögren's syndrome contain antibodies in their sera directed against certain normal cellular components such as the La/SS-B autoantigen, an RNA-binding protein believed to function as a putative processor of RNA polymerase III precursor transcripts. We have identified cDNA clones from the fruit fly Drosophila melanogaster that encode a protein displaying significant sequence homology with human La/SS-B. The fly protein (which we refer to as D-La) contains a putative ribonucleoprotein 1 (RNP1) and RNP2 RNA-binding domain. D-La also possesses a leucine zipper motif, suggesting that it may interact with itself or other proteins. Using gel retardation analysis, we show that D-La can bind RNA; in addition, we demonstrate the first reported DNA-binding activity associated with a La protein. Northern (RNA) blot analysis revealed a single 1,600-nucleotide transcript expressed throughout embryonic, larval, pupal, and adult development. Surprisingly, whole-mount in situ hybridization experiments revealed that D-La transcripts are not present in all ovarian tissues. In addition, early expression throughout the embryo is followed by a restricted pattern of mesodermal expression that is later confined to the visceral mesoderm, gonads, gut, and salivary glands. These results suggest that D-La may play a more specialized role during fly development as opposed to a rather general role inferred by its homology to La proteins from other organisms.

[Histochemical studies on the glycoconjugates of experimental alkali burned cornea in rabbit]

The model of experimental alkali burn of cornea in rabbit was obtained using 1 mol/L NaOH solution. After being burned for 1, 3, 7 and 14 days, the histochemical changes of these models were studied by using labelled concanavalin A (ConA-FITC) and wheat germ agglutinin (WGA-FITC). The results showed that after being burned, the amount of glycoconjugates interacted with these lectins decreased, and increased gradually after 7 days, then reached the level higher than that in the normal cornea. These changes were related to the recovery of alkali burned cornea.

Individual serum bile acids as early indicators of carbon tetrachloride- and chloroform-induced liver injury

Individual serum bile acids (SBA) are emerging as potentially useful early indicators of liver injury. This study was undertaken to compare the usefulness of individual SBA with the routinely used assays for detecting the effects of the hepatotoxicants carbon tetrachloride (CCl4) and chloroform (CHCl3). Serum samples were assayed for liver injury by determination of alanine aminotransferase (ALT), aspartate amino-transferase (AST), alkaline phosphatase (ALP), bilirubin and total bile acid (by enzymatic kit). These results were compared with levels of individual SBA measured by high performance liquid chromatography (HPLC). Liver samples from CCl4-treated rats were taken for light and electron microscopic examination. The highest dose for each chemical caused increases in serum ALT and AST but not ALP. Chloroform at the highest dose increased bilirubin. Total SBA levels as assayed by the kit were elevated in response to CCl4 and CHCl3 at doses below which serum enzymes and bilirubin were increased. Some individual SBA were increased at a still lower dose for each of these two chlorinated solvents. At the lowest dose of CCl4 tested no consistent light microscopic or ultrastructural changes were found. At all the higher doses periacinar cells displayed typical accumulation of lipid droplets and degranulation and dilation of rough endoplasmic reticulum. The extent of the ultrastructural changes were dose-dependent. Thus individual SBA assayed by HPLC may be considered as a very sensitive indicator of liver injury induced by the classical hepatotoxicants carbon tetrachloride and chloroform.

Glutathione protection in alveolar type II cells from fetal and neonatal rabbits

Previous studies have demonstrated a correlation between intracellular glutathione (GSH) pools and sensitivity to oxidative injury. In the present study, we demonstrated that de novo GSH synthesis or GSH uptake could increase intracellular GSH by 7- and 19-fold, respectively, in type II cells from neonatal rabbits. This suggested that the rate of GSH uptake was against a concentration gradient and greater than the synthetic rate. This increased intracellular GSH was associated with protection from oxidant injury by paraquat or 80% O2. A relationship between GSH uptake and protection was further supported by blockage of both processes by gamma-L-glutamyl-L-glutamate, a GSH analogue. With a greater oxidative burden, both de novo synthesis and GSH uptake were required to maintain protection. Although the transport rate was only 6% of that for neonatal cells, cells from fetal animals transported GSH and were protected from oxidative injury. From these results we conclude there was a causal relationship between GSH transport and protection from oxidative injury in type II cells from neonatal and fetal animals.

Stimulation of glutathione absorption in rat small intestine by alpha-adrenergic agonists

The alpha-adrenergic agonist, phenylephrine (1.6 microM), caused a threefold stimulation of glutathione (GSH) transport from the lumen into the vasculature in isolated, vascularly perfused rat small intestine. Stimulation of GSH transport by phenylephrine was blocked by the alpha-adrenergic antagonists, prazosin or phentolamine. Norepinephrine and epinephrine (both alpha and beta agonists) also stimulated GSH absorption but not to the same extent as phenylephrine. Isoproterenol, a strict beta-adrenergic agonist, had no effect on the rate of GSH absorption. Under physiological luminal GSH concentrations, phenylephrine stimulated GSH efflux from the lumen, accumulation in the intestinal mucosa, and transport into the mesenteric vasculature. Phenylephrine did not stimulate the transport of polyethylene glycol, a high molecular weight molecule, and stimulated uptake of cysteine and glycine by 30%. This suggests that the effect of phenylephrine on GSH transport is not due to enhanced bulk flow through paracellular pathways. Studies with isolated small intestinal epithelial cells showed that phenylephrine also stimulated the release of GSH from the cells. Oral administration of phenylephrine with GSH caused a two- to fivefold transient increase in plasma GSH concentrations in rats. Phenylephrine alone or with the amino acid constituents of GSH caused no increase in plasma GSH concentration. Thus, absorption of dietary GSH is under hormonal regulation. The physiological importance of this regulation is not known, although such regulation may function to control utilization of dietary GSH for detoxication and may have therapeutic benefits for individuals with deficient GSH or increased risk of oxidative or chemically induced injury.

Fractionation and analysis of mitochondria with polycarbonate membrane filters

Polycarbonate membrane filters were used to fractionate mitochondrial populations depending on their aggregation or association with other subcellular structures. Isolated rat liver mitochondria penetrated through filters which have pore sizes larger than 1 micron. In contrast, mitochondria which were induced to aggregate in vitro by incubation at low pH were retained by the filters and thus could be separated from the single or small aggregates of mitochondria. Use of this membrane filtration method to analyze release of mitochondria from isolated hepatocytes showed that treatment with digitonin at concentrations only sufficient to lyse the plasma membrane did not release mitochondria. Homogenization or sonication following digitonin treatment released 25-50% of the mitochondria, but only a small fraction was intact. A high yield of intact mitochondria was released from digitonin-treated cells by a brief treatment with a low concentration of the proteolytic enzyme nagarse. Thus, this membrane filtration method provides a simple and rapid approach to analyze the extent of mitochondrial aggregation and association with other subcellular structures.