Membrane localization of the pertussis toxin-sensitive G-protein subunits alpha i-2 and alpha i-3 and expression of a metallothionein-alpha i-2 fusion gene in LLC-PK1 cells

The renal epithelial cell line LLC-PK1 has topographically distinct regulatory roles for the alpha subunits of pertussis toxin-sensitive guanine nucleotide regulatory proteins (alpha i subunit); these include the inhibition of adenylyl cyclase at the basolateral membrane and the stimulation of Na+ channel activity at the apical membrane. We now report that LLC-PK1 cells contain two members of the alpha i protein family, alpha i-2 and alpha i-3, which have distinct cellular locations consistent with their diverse functional roles. By using specific alpha i antibodies and immunofluorescence, the alpha i-2 subunit was found to be localized to the basolateral membrane, whereas the alpha i-3 subunit was concentrated in the Golgi and was also detectable at low levels on apical membranes in some cells. Induction of a chimeric mouse metallothionein 1-rat or canine alpha i-2 gene stably transfected into the LLC-PK1 cells produced an increase in the content of the alpha i-2 subunit, which was targeted only to the basolateral membrane. These findings suggest that alpha i subunit specificity for effectors may be achieved in polarized renal epithelial cells by their geographic segregation to different cellular membranes. The LLC-PK1 cell stably transfected with the metallothionein-alpha i-2 fusion gene will provide a model for the study of guanine nucleotide regulatory protein function in epithelia.

Prognostic implications of postoperative suppression of arterial ketone body ratio: time factor involved in the suppression of hepatic mitochondrial oxidation-reduction state

To determine the tolerance limit of the liver in the critically suppressed mitochondrial oxidation-reduction state, the arterial ketone body ratio (acetoacetate/3-hydroxybutyrate), which reflects hepatic mitochondrial oxidation-reduction potential, was measured 1319 times in 161 patients during the postoperative critical period. Because patients who showed arterial ketone body ratios between 0.40 and 0.25 had a higher incidence of postoperative complications than had those who showed ratios above 0.40, this was designated as the critical zone of the arterial ketone body ratio. When duration in the critical zone was less than 2 days, 90% of the patients were able to tolerate the condition and survive. By contrast, when an arterial ketone body ratio below 0.40 was prolonged for more than 5 days, there was a high incidence of multiple organ failure and a 100% mortality rate, with the average survival period after a 5-day suppression being estimated as 5.7 +/- 2.4 days. It is suggested that the arterial ketone body ratio in the critical zone must be returned to normal values within 2 days to obtain a good prognosis.

[Synthesis, cloning and expression of human alpha-atrial natriodiuretic peptide gene in yeast system]

Human alpha-ANP was synthesised using a yeast system. In order to obtain correct expression of the human alpha-ANP gene, a few bases on one strand were substituted by the corresponding yeast sequence, but those bases were not replaced in the complementary so a few unpaired bases existed. The gene was cloned into a shuttle vector (with alpha-factor). The recombinants containing different human alpha-ANP DNA sequences were separated by BglII restriction analysis. We compared the expression level of human alpha-ANP from two kinds of genes and the results showed that the ANP expression level by the gene containing yeast sequences was lower (0.5-0.7 mg/L) than that expressed by the original gene (0.8-1.0 mg/L).

Influence of dopamine on the liver assessed by changes in arterial ketone body ratio in brain-dead dogs

The influence of dopamine on liver metabolism in the state of brain death was assessed by measuring arterial ketone body ratio (AKBR) in dogs. Mean arterial blood pressure (MABP) was significantly decreased, from 137.4 +/- 3.7 to 64.7 +/- 2.8 mm Hg, 1 hour after completion of brain death (p less than 0.01). In the control group AKBR was maintained at the near control value of 1.07 thereafter, concomitant with a significant decrease in serum lactate levels, despite marked hypotension (p less than 0.05). Dopamine infusion at rates of 5 and 10 micrograms/kg/min sustained both AKBR and MABP at near control values. In contrast, dopamine given at doses greater than 15 micrograms/kg/min caused a significant reduction of AKBR, to less than 0.66 +/- 0.12 (p less than 0.01), although MABP was restored to near-normal levels. In addition, serum levels of alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase were significantly elevated, reflecting liver cell injury. It is suggested that the liver is primarily tolerant to hypotension in the state of brain death and that dopamine administered at a rate of 15 micrograms/kg/min or more impairs liver metabolism by reducing the redox state (free nicotinamide-adenine dinucleotide/reduced nicotinamide-adenine dinucleotide) of liver mitochondria.

A 165-base pair sequence between the dihydrofolate reductase gene and the divergently transcribed upstream gene is sufficient for bidirectional transcriptional activity

The dihydrofolate reductase gene encodes a key enzyme of one-carbon metabolism and is constitutively expressed in all cells. Recently, transcripts initiated at 89 base pairs upstream from the transcriptional initiation site of the dihydrofolate reductase gene and transcribed from the opposite strand have been identified and shown to encode for a protein with homology to a bacterial DNA mismatch repair enzyme (Fujii, H., and Shimada, T. (1989) J. Biol. Chem. 264, 10057-10064). Therefore, the two genes are organized in a head-to-head configuration separated by an 89-base pair segment. The promoter activities of this short spacer sequence were studied in a transient assay using the chloramphenicol acetyltransferase and the guanine phosphoribosyltransferase genes as reporters. A 165-base pair fragment from -111 to +54 relative to the dihydrofolate reductase initiation site was shown to be sufficient for transcriptional activity in either direction, suggesting that expression of the two divergent genes is regulated by a bidirectional promoter that may use common regulatory elements.

An electrophoretic karyotype and assignment of ribosomal genes to resolved chromosomes of Pneumocystis carinii

Pulsed-field gel electrophoresis was used to generate a molecular karyotype of chromosomes from the opportunistic AIDS pathogen, Pneumocystis carinii. P. carinii cysts and trophozoites were isolated from immunosuppressed rats, lysed in situ in agarose blocks, and subjected to orthogonal-field gel electrophoresis (OFAGE) and contour-clamped homogeneous-field gel electrophoresis (CHEF). OFAGE and CHEF gels resolved, respectively, 16 or 20 chromosome bands ranging in size from 0.32-1.5 megabase pairs. Summation of the estimated sizes of these chromosomes suggested a total genome complexity for P. carinii of 8-16 megabase pairs. Homologous probes for the genes encoding the 18S, 5.8S, and 5S ribosomal RNAs were hybridized to filter blots of the pulsed-field gels to map these genes to specific P. carinii chromosomes.

An ELISA method for the quantitation of tracheal mucins from human and nonhuman primates

Monoclonal antibodies, 17B1 and 17Q2, which are specific for large molecular weight mucous glycoproteins of airway epithelium, have been used to develop an ELISA method to quantitate the tracheal mucins of humans and rhesus monkeys. The assay is a double-sandwich system that does not depend on either the binding of mucous antigens to the microtiter plate or the use of a second antibody. The assay protocol includes (1) coating the microtiter well with purified IgG of 17B1 or 17Q2, (2) incubating the wells with mucous samples, (3) binding of alkaline phosphatase-conjugated IgG to the wells, and (4) developing the color with phosphate substrate. This ELISA method is very sensitive for human and rhesus monkey tracheal mucins. Quantitation is not affected by the presence of various proteoglycans (keratan sulfate, hyaluronate, heparin, heparan sulfate, and chondroitin sulfate). However, the quantitation is affected by the treatment of antigen with periodic acid and endo-beta-galactosidase. Other enzymes (e.g., neuraminidase, hyaluronidase, chondroitinase, heparitinase, heparinase, fucosidase, keratanase) have no effect on the antigenicity of substrate. The quantitation is linear, with a concentration from 0.2 to 4 ng protein/sample. The ELISA method developed in this study should be useful for quantitating the mucin content of various biologic fluids, such as sputum, bronchoalveolar lavage, and media from cultures following various pharmacologic and physiologic manipulations.

Responses of the working rat heart to carbon monoxide

The effects of carbon monoxide (CO) were studied in the isolated working rat heart. Hearts removed from male laboratory rats were perfused via the left atrium with Krebs-Henseleit solution (KH) oxygenated with 95% O2-5% CO2 (O2). Heart rate and arterial pressures were measured by a transducer inserted in the aortic outflow line and connected to a data logger. Aortic flow was determined by collecting the effluent from the aortic bubble trap in a graduated cylinder. Coronary flow through the pulmonary cannula was collected and measured in a graduated cylinder. After 30 min, the hearts were challenged with solutions containing either CO (5% CO-90% O2-5% CO2) or N2 (5% N2-90% O2-5% CO2) for 10 min (Challenge I). After recovery in O2, the hearts were challenged with the alternate test solution (Challenge II). CO increased coronary flow (CF) and coronary flow as a percent of cardiac output (CF%) 13 and 16% respectively. N2 had no significant effect on CF or CF%. CO and N2 had no significant effect on heart rate, cardiac output, oxygen consumption or on aortic flow or pressure. These results indicate that vasodilation is the major response of the working heart to CO, and this response is not mediated by simple hypoxia.

Apical electrogenic NaHCO3 cotransport. A mechanism for HCO3 absorption across the retinal pigment epithelium

Intracellular microelectrode techniques and intracellular pH (pHi) measurements using the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) were employed to characterize an electrogenic bicarbonate transport mechanism at the apical membrane of the frog retinal pigment epithelium (RPE). Reductions in apical concentrations of both [HCO3]o (at constant Pco2 or pHo) or [Na]o caused rapid depolarization of the apical membrane potential (Vap). Both of these voltage responses were inhibited when the concentration of the other ion was reduced or when 1 mM diisothiocyano-2-2 disulfonic acid stilbene (DIDS) was present in the apical bath. Reductions in apical [HCO3]o or [Na]o also produced a rapid acidification of the cell interior that was inhibited by apical DIDS. Elevating pHi at constant Pco2 (and consequently [HCO3]i) by the addition of apical NH4 (20 mM) produced an immediate depolarization of Vap. This response was much smaller when either apical [HCO3]o or [Na]o was reduced or when DIDS was added apically. These results strongly suggest the presence of an electrogenic NaHCO3 cotransporter at the apical membrane. Apical DIDS rapidly depolarized Vap by 2-3 mV and decreased pHi (and [HCO3]i), indicating that the transporter moves NaHCO3 and net negative charge into the cell. The voltage dependence of the transporter was assessed by altering Vap with transepithelial current and then measuring the DIDS-induced change in Vap. Depolarization of Vap increased the magnitude of the DIDS-induced depolarization, whereas hyperpolarization decreased it. Hyperpolarizing Vap beyond -114 mV caused the DIDS-induced voltage change to reverse direction. Based on this reversal potential, we calculate that the stoichiometry of the transporter is 1.6-2.4 (HCO3/Na).

Hepatic tolerance to hypotension as assessed by the changes in arterial ketone body ratio in the state of brain death

Hepatic tolerance to hypotension was assessed by changes in arterial ketone body ratio (KBR) and hepatic energy charge levels in experimental brain death induced by epidural ballooning in dogs, and compared with the hemorrhagic shock model. Systolic arterial blood pressure was significantly decreased from 182 mmHg to 67 mmHg after completion of brain death (P less than 0.01), but KBR was maintained at near the control value of 1.098 +/- 0.051 in spite of marked hypotension. Hepatic energy charge was 0.846 +/- 0.016 and remained at normal level. No significant changes were observed in lactate level, total bilirubin, SGPT, and LDH. SGOT was slightly elevated but was still within normal limits (P less than 0.05). Light microscopic examination revealed no apparent ischemic change in the centrilobular region under hematoxylin and eosin staining. By contrast, KBR decreased from 0.975 +/- 0.054 to 0.273 +/- 0.060 following hypotension in the Wiggers' shock model (P less than 0.01). Lactate levels were gradually elevated significantly (P less than 0.05), but no significant increases were observed in total bilirubin, SGOT, SGPT, and LDH. It is suggested that the hepatic energy status is well maintained in the state of brain death, in which state the liver has high tolerance to marked hypotension until shortly before stoppage of the heart.

Cloning and analysis of fs(1) Ya, a maternal effect gene required for the initiation of Drosophila embryogenesis

The maternal effect locus fs(1) Ya is required for the fusion of the apposed sperm and egg pronuclei (syngamy) following fertilization in Drosophila. It is tightly linked to another complementation group, fs(1) Yb, needed for both oogenesis and embryogenesis. We have isolated a set of overlapping cloned sequences in the 3B4-6 region of the X chromosome encompassing the fs(1) Ya-fs(1) Yb region. A single 2.4 kb maternal transcript is encoded within this region, and an 8.5 kb DNA fragment that contains this transcript complements both fs(1) Ya and fs(1) Yb mutations. Northern and in situ hybridization analyses show that the maternal transcript is only present in nurse cells and oocytes beginning in previtellogenic stages, and is evenly distributed in the cytoplasm of 0-2 h syncytial embryos. The transcript is not detected in later stages of embryonic development. This expression pattern correlates closely with the genetic and developmental characteristics expected of the fs(1) Ya gene product.

Eutectic phase behavior of 1-stearoyl-2-caprylphosphatidylcholine and dimyristoylphosphatidylcholine mixtures

The thermotropic behavior of aqueous dispersions of C(18):C(10)PC/diC(14)PC mixtures with different molar ratios has been investigated by high-resolution differential scanning calorimetry. C(18):C(10)PC is a highly asymmetric lipid molecule, whereas diC(14)PC is a symmetric species with the same molecular weight. Their packing properties in the bilayer are known to be similar at T greater than Tm, but very dissimilar at T less than Tm. Calorimetric results indicate that C(18):C(10)PC and diC(14)PC are completely miscible in the liquid-crystalline state. In the gel state, however, C(18):C(10)PC and diC(14)PC are only partially miscible. The temperature-composition phase diagram for C(18):C(10)PC/diC(14)PC mixtures has the shape characteristic of a typical eutectic system.

Carbon monoxide effects on calcium levels in vascular smooth muscle

Previously we showed that carbon monoxide (CO) relaxes vascular smooth muscle in the working heart and thoracic aorta preparations perfused with hemoglobin-free, Krebs-Henseleit (KH) solution. The CO-induced relaxation was not caused by hypoxia, nor was it mediated by adrenergic influences, adenosine, or prostaglandins. In these studies the effect of CO on calcium (Ca++) concentrations in vascular smooth muscle was determined using 45Ca as a tracer. Isolated rat thoracic aorta segments were incubated with 45Ca and gassed with O2, N2, or CO for 60 min. Verapamil was used to verify the effectiveness of the test system. Ca++ concentrations were 488 +/- 35 and 515 +/- 26 mM/g tissue (X +/- SE) in aortic rings gassed with O2 and N2, respectively. CO reduced Ca++ concentrations significantly (P less than 0.01) by 29% to 369 +/- 18 mM/g tissue. Verapamil treatment reduced Ca++ concentrations by 40% to 314 +/- 23 mM/g tissue. These results suggest that CO relaxes vascular smooth muscle and dilates blood vessels by decreasing Ca++ concentrations in vascular smooth muscle.

The mechanism of peroxidase-mediated cytotoxicity. II. Role of the heme moiety

Various peroxidases in the presence of hydrogen peroxide and a halide ion have been shown to exert a cytolytic activity against erythrocytes and other cells. However, few studies have been done to elucidate the active site on the enzymes that is responsible for the cytotoxic activity. In addressing this question we found that boiling of horseradish peroxidase only partially abolishes its cytotoxic activity, suggesting that an intact tertiary structure of the protein may not be essential for the cytotoxic activity. This conclusion was confirmed by demonstrating that microperoxidase, hemin, and hematoheme also exert cytotoxic activity in the presence of hydrogen peroxide and iodide, the kinetics of which were identical to those obtained with the peroxidases. Fluoride, bromide, and thiocyanate could not replace iodide in any of these systems. These results indicate that the active site for the cytotoxic activity of the peroxidases is located within the heme moiety, whereas the protein portions of the enzymes affect the cytotoxic activity of the enzymes only in an indirect manner. We also tested a variety of compounds for their ability to inhibit the cytolytic reaction toward erythrocytes. We found that compounds such as thiourea, thionicotinamide, and uric acid are much more potent inhibitors of the cytolytic reaction than tyrosine and histidine. These observations support the concept that oxidative reactions rather than halogenation reactions are the primary cause of the peroxidase-mediated lysis of erythrocytes.

Vasodilating effects of carbon monoxide

The vasodilator effects of carbon monoxide (CO) were studied in an isolated perfused rat thoracic aorta preparation. Thoracic aortas from male Sprague-Dawley laboratory rats were dissected free of surrounding tissue, cannulated proximally, and tethered to in situ length. The vessels were perfused with oxygenated Krebs-Henseleit (KH) solution at 37 degrees C in a constant flow system with a circumferentially-applied, pulsatile (300/min), basal "systolic" pressure of 100 mm Hg. Aortas were precontracted with high-potassium (K+) or norepinephrine (NE). Changes in perfusion pressure were indicative of changes in vascular resistance induced by the test gas mixtures. Oxygen (O2) content of the perfusate was kept constant, while CO and nitrogen (N2) were altered. CO (2.5, 5 and 10%) dilated both K+-contracted and NE-contracted aortas in a dose-dependent manner. A significant vasodilation in response to 5% CO (24.5% of maximal), but not to 5% N2, was obtained in the K+-contracted aortas. After the endothelium was removed chemically, the aortas continued to dilate in response to CO. These results suggest that CO has a direct vasorelaxant effect on vascular smooth muscle which is nonspecific and is not endothelium-dependent.

The cytotoxic activity of hematoheme: evidence for two different mechanisms

Hematoheme displays a potent cytolytic activity toward erythrocytes either in the presence of hydrogen peroxide and a halide ion (system I) or in the presence of oxygen and a reducing agent (system II). In system I it resembles the cytotoxic activity of various peroxidases, whereas in system II it resembles the destructive activity of bleomycin and a variety of metal complexes. Both types of reactions presumably involve the generation of active oxygen species, which are responsible for the damaging effects. In a first attempt to compare the chemical mechanisms of the two types of reactions we used various traps and scavengers of active oxygen species. Tryptophan as well as tyrosine and uric acid were found to be potent inhibitors of the hematoheme-H2O2-halide reaction but do not significantly inhibit the hematoheme-O2-ascorbate reaction. Pyridine, on the other hand, inhibits the oxygen-mediated reaction, but does not affect the peroxide-halide-mediated activity. The cytolytic activity of photoactivated hematoporphyrin, which involves the generation of singlet oxygen, is activated by pyridine and is strongly inhibited by diphenylisobenzofuran. The latter compound is a weak activator of both hematoheme reactions. We conclude that the two hematoheme reactions proceed by two different mechanisms and probably generate different toxic intermediates. The results further suggest that the toxic intermediate generated by photoactivated hematoporphyrin (singlet oxygen) does not play a dominant role in either of the two hematoheme reactions.

The mechanism of peroxidase-mediated cytotoxicity. I. Comparison of horseradish peroxidase and lactoperoxidase

The kinetics of the cytolytic activity expressed by lactoperoxidase and horseradish peroxidase toward erythrocytes in the presence of H2O2 and iodide have been investigated at physiological pH. The action of both enzymes was found to be very similar with respect to their kinetic mechanisms. Both enzymes showed saturation kinetics at higher enzyme concentrations under conditions where substrate concentrations were not limiting. Optimal concentrations of H2O2 and iodide were found to be 40 and 25 microM, respectively, for both enzymes. Higher concentrations of H2O2 inhibited the cytolytic activity. The pH dependence of the cytolytic reaction is also very similar for both enzymes, showing maximal activity at about pH 6.3. Moreover, the cytolytic activities of both enzymes were inhibited by tyrosine, tryptophan, cysteine, and to a lesser extent by histidine. We conclude from these data that the mechanisms of horseradish peroxidase and lactoperoxidase in promoting the lysis of erythrocytes are closely related if not identical.

The cytotoxic activity of hematoporphyrin: studies on the possible role of transition metals

Hematoporphyrin acquires a potent cytolytic activity toward erythrocytes when activated by visible light. Considerable evidence has been obtained suggesting that this toxic activity is mediated by certain active oxygen species, including singlet oxygen and hydroxyl radicals. These active oxygen species have also been proposed as intermediates in the toxic activity of peroxidases, hemin, and a variety of metal complexes. Unlike hematoporphyrin, all these compounds contain a liganded Fe atom, which appears to play a central role in the activation of molecular oxygen. In order to ascertain whether the generation of active oxygen by hematoporphyrin may also involve the participation of a metal ion we have compared the cytolytic activity of hematoporphyrin with that of hematoheme. The participation of a metal ion in the light-activated hematoporphyrin reaction was ruled out on the basis of four criteria: no increase in cytolytic activity was observed upon the addition of Fe or Cu ions; no evidence could be obtained for the incorporation of a metal ion into hematoporphyrin during light activation; hematoporphyrin is a more potent cytolytic agent than hematoheme on an equimolar basis; and the activities of the two cytolytic agents are affected differently by various activators and inhibitors of the toxic reaction. Our results further indicate that the mechanism of the cytolytic activity promoted by light-activated hematoporphyrin is distinctly different from that promoted by hematoheme in the presence of ascorbate. We conclude that the two cytolytic reactions are most likely propagated by two different forms of active oxygen.