Guanine quadruplexes mediate mitochondrial RNA polymerase pausing

The information content within nucleic acids extends beyond the primary sequence to include secondary structures with functional roles in cells. Guanine-rich sequences form structures called guanine quadruplexes (G4) that result from non-canonical base pairing between guanine residues. These stable structures are enriched in gene promoters and have been correlated with the locations of RNA polymerase II pausing (Pol II). While promoter-proximal RNA polymerase pausing regulates gene expression, the effects of guanine quadruplexes on gene transcription have been less clear. We determined the pattern of mitochondrial RNA polymerase (mtRNAP) pausing in human fibroblasts and found that it pauses over 400 times on the mitochondrial genome. We identified quadruplexes as a mediator of mtRNAP pausing and show that stabilization of quadruplexes impeded transcription by mtRNAP. Gene products encoded by the mitochondrial genome are required for oxidative phosphorylation and the decreased transcription by mtRNAP resulted in lower expression of mitochondrial genes and significantly reduced ATP generation. Energy from mitochondria is essential for transport function in renal epithelia, and impeded mitochondrial transcription inhibits transport function in renal proximal tubule cells. These results link formation of guanine quadruplex structures to regulation of mtRNAP elongation and mitochondrial function.

Rethinking Vasopressin: New Insights into Vasopressin Signaling and Its Implications

Vasopressin is a highly conserved peptide hormone that has been traditionally associated with water homeostasis. There is accumulating evidence in both humans and animal models that vasopressin is implicated in the regulation of metabolism. This review focuses on the effects that vasopressin exerts on the regulation of glucose and fatty acids with a particular emphasis on the potential repercussions of metabolic dysregulation in kidney disease.

Insulin-regulated aminopeptidase is required for water excretion in response to acute hypotonic stress

The objective of this study was to understand the response of mice lacking insulin-regulated aminopeptidase (IRAP) to an acute water load. For mammals to respond appropriately to acute water loading, vasopressin activity needs to decrease. IRAP degrades vasopressin in vivo. Therefore, we hypothesized that mice lacking IRAP have an impaired ability to degrade vasopressin and, thus, have persistent urinary concentration. Age-matched 8- to 12-wk-old IRAP wild-type (WT) and knockout (KO) male mice were used for all experiments. Blood electrolytes and urine osmolality were measured before and 1 h after water load (∼2 mL sterile water via intraperitoneal injection). Urine was collected from IRAP WT and KO mice for urine osmolality measurements at baseline and after 1 h administration of the vasopressin type 2 receptor antagonist OPC-31260 (10 mg/kg ip). Immunofluorescence and immunoblot analysis were performed on kidneys at baseline and after 1 h acute water load. IRAP was expressed in the glomerulus, thick ascending loop of Henle, distal tubule, connecting duct, and collecting duct. IRAP KO mice had elevated urine osmolality compared with WT mice due to higher membrane expression of aquaporin 2 (AQP2), which was restored to that of controls after administration of OPC-31260. IRAP KO mice developed hyponatremia after an acute water load because they were unable to increase free water excretion due to increased surface expression of AQP2. In conclusion, IRAP is required to increase water excretion in response to an acute water load due to persistent vasopressin stimulation of AQP2.NEW & NOTEWORTHY Insulin-regulated aminopeptidase (IRAP) degrades vasopressin, but its role in urinary concentration and dilution is unknown. Here, we show that IRAP-deficient mice have a high urinary osmolality at baseline and are unable to excrete free water in response to water loading. These results reveal a novel regulatory role for IRAP in urine concentration and dilution.

Kidney collecting duct cells make vasopressin in response to NaCl-induced hypertonicity

Vasopressin has traditionally been thought to be produced by the neurohypophyseal system and then released into the circulation where it regulates water homeostasis. The questions of whether vasopressin could be produced outside of the brain and if the kidney could be a source of vasopressin are raised by the syndrome of inappropriate antidiuretic hormone secretion (vasopressin). We found that mouse and human kidneys expressed vasopressin mRNA. Using an antibody that detects preprovasopressin, we found that immunoreactive preprovasopressin protein was found in mouse and human kidneys. Moreover, we found that murine collecting duct cells made biologically active vasopressin, which increased in response to NaCl-mediated hypertonicity, and that water restriction increased the abundance of kidney-derived vasopressin mRNA and protein expression in mouse kidneys. Thus, we provide evidence of biologically active production of kidney-derived vasopressin in kidney tubular epithelial cells.

A common transcriptional mechanism involving R-loop and RNA abasic site regulates an enhancer RNA of APOE

RNA is modified by hundreds of chemical reactions and folds into innumerable shapes. However, the regulatory role of RNA sequence and structure and how dysregulation leads to diseases remain largely unknown. Here, we uncovered a mechanism where RNA abasic sites in R-loops regulate transcription by pausing RNA polymerase II. We found an enhancer RNA, AANCR, that regulates the transcription and expression of apolipoprotein E (APOE). In some human cells such as fibroblasts, AANCR is folded into an R-loop and modified by N-glycosidic cleavage; in this form, AANCR is a partially transcribed nonfunctional enhancer and APOE is not expressed. In contrast, in other cell types including hepatocytes and under stress, AANCR does not form a stable R-loop as its sequence is not modified, so it is transcribed into a full-length enhancer that promotes APOE expression. DNA sequence variants in AANCR are associated significantly with APOE expression and Alzheimer's Disease, thus AANCR is a modifier of Alzheimer's Disease. Besides AANCR, thousands of noncoding RNAs are regulated by abasic sites in R-loops. Together our data reveal the essentiality of the folding and modification of RNA in cellular regulation and demonstrate that dysregulation underlies common complex diseases such as Alzheimer's disease.

Clinical and Molecular Aspects of Senataxin Mutations in Amyotrophic Lateral Sclerosis 4

Objective

To determine the clinical and molecular features in patients with amyotrophic lateral sclerosis 4 (ALS4) due to mutations in the senataxin (SETX) gene and to develop tools for evaluating SETX variants.

Methods

Our study involved 32 patients, including 31 with mutation in SETX at c.1166 T>C (p.Leu389Ser) and 1 with mutation at c.1153 G>A (p.Glu385Lys). Clinical characterization of the patients included neurological examination, blood tests, magnetic resonance imaging (MRI), and dual‐energy x‐ray absorptiometry (DEXA). Fibroblasts and motor neurons were obtained to model the disease and characterize the molecular alteration in senataxin function.

Results

We report key clinical features of ALS4. Laboratory analysis showed alteration of serum creatine kinase and creatinine in the Leu389Ser ALS4 cohort. MRI showed increased muscle fat fraction in the lower extremities, which correlates with disease duration (thigh fat fraction R² = 0.35, p = 0.01; lower leg fat fraction R² = 0.49, p < 0.01). DEXA measurements showed lower extremities are more affected than upper extremities (average fat z scores of 2.1 and 0.6, respectively). A cellular assay for SETX function confirmed that like the Leu389Ser mutation, the Glu385Lys variant leads to a decrease in R loops, likely from a gain of function.

Interpretation

We identified clinical laboratory and radiological features of ALS4, and hence they should be monitored for disease progression. The molecular characterization of R‐loop levels in patient‐derived cells provides insight into the disease pathology and assays to evaluate the pathogenicity of candidate mutations in the SETX gene. ANN NEUROL 2020;87:547–555

cis Elements that Mediate RNA Polymerase II Pausing Regulate Human Gene Expression

Aberrant gene expression underlies many human diseases. RNA polymerase II (Pol II) pausing is a key regulatory step in transcription. Here, we mapped the locations of RNA Pol II in normal human cells and found that RNA Pol II pauses in a consistent manner across individuals and cell types. At more than 1,000 genes including MYO1E and SESN2, RNA Pol II pauses at precise nucleotide locations. Characterization of these sites shows that RNA Pol II pauses at GC-rich regions that are marked by a sequence motif. Sixty-five percent of the pause sites are cytosines. By differential allelic gene expression analysis, we showed in our samples and a population dataset from the Genotype-Tissue Expression (GTEx) consortium that genes with more paused polymerase have lower expression levels. Furthermore, mutagenesis of the pause sites led to a significant increase in promoter activities. Thus, our data uncover that RNA Pol II pauses precisely at sites with distinct sequence features that in turn regulate gene expression.

Senataxin Mutation Reveals How R-Loops Promote Transcription by Blocking DNA Methylation at Gene Promoters

R-loops are three-stranded nucleic acid structures found abundantly and yet often viewed as by-products of transcription. Studying cells from patients with a motor neuron disease (amyotrophic lateral sclerosis 4 [ALS4]) caused by a mutation in senataxin, we uncovered how R-loops promote transcription. In ALS4 patients, the senataxin mutation depletes R-loops with a consequent effect on gene expression. With fewer R-loops in ALS4 cells, the expression of BAMBI, a negative regulator of transforming growth factor β (TGF-β), is reduced; that then leads to the activation of the TGF-β pathway. We uncovered that genome-wide R-loops influence promoter methylation of over 1,200 human genes. DNA methyl-transferase 1 favors binding to double-stranded DNA over R-loops. Thus, in forming R-loops, nascent RNA blocks DNA methylation and promotes further transcription. Hence, our results show that nucleic acid structures, in addition to sequences, influence the binding and activity of regulatory proteins.

The Pioneer Transcription Factor FoxA Maintains an Accessible Nucleosome Configuration at Enhancers for Tissue-Specific Gene Activation

Nuclear DNA wraps around core histones to form nucleosomes, which restricts the binding of transcription factors to gene regulatory sequences. Pioneer transcription factors can bind DNA sites on nucleosomes and initiate gene regulatory events, often leading to the local opening of chromatin. However, the nucleosomal configuration of open chromatin and the basis for its regulation is unclear. We combined low and high levels of micrococcal nuclease (MNase) digestion along with core histone mapping to assess the nucleosomal configuration at enhancers and promoters in mouse liver. We find that MNase-accessible nucleosomes, bound by transcription factors, are retained more at liver-specific enhancers than at promoters and ubiquitous enhancers. The pioneer factor FoxA displaces linker histone H1, thereby keeping enhancer nucleosomes accessible in chromatin and allowing other liver-specific transcription factors to bind and stimulate transcription. Thus, nucleosomes are not exclusively repressive to gene regulation when they are retained with, and exposed by, pioneer factors.

Effects of angiotensin (1-7) upon right ventricular function in experimental rat pulmonary embolism

Right ventricular (RV) dysfunction contributes to poor clinical prognosis after pulmonary embolism (PE). The present studies evaluate the effects of angiotensin (1-7) (ANG (1-7)) upon RV function during experimental PE in rats. Circulating ANG II increased 8-fold 6 hr after PE (47±13 PE vs. 6±3 pg/mL, control, p<0.05). ACE2 protein was uniformly localized in the RV myocardium of control rats, but showed a patchy distribution with some cells devoid of stain after 6 or 18 hr of PE. RV function decreased 18 hr after PE compared with control treated animals (19±4 vs. 41±1 mmHg, respectively, p<0.05; 669±98 vs. 1354±77 mmHg/sec, respectively, p<0.05), while left ventricular function (LV) was not significantly changed. Animals treated with ANG (1-7) during PE showed improved RV +dP/dt and peak systolic pressure development to values not significantly different from control animals. Protection of RV function by ANG (1-7) was associated with improved arterial blood sO2, base excess and pH. Supplemental delivery of ANG (1-7) reduced the development of RV dysfunction, suggesting a novel approach to protecting RV function in the setting of acute experimental PE.

Transcriptional competence and the active marking of tissue-specific enhancers by defined transcription factors in embryonic and induced pluripotent stem cells

We reported previously that well-characterized enhancers but not promoters for typical tissue-specific genes, including the classic Alb1 gene, contain unmethylated CpG dinucleotides and evidence of pioneer factor interactions in embryonic stem (ES) cells. These properties, which are distinct from the bivalent histone modification domains that characterize the promoters of genes involved in developmental decisions, raise the possibility that genes expressed only in differentiated cells may need to be marked at the pluripotent stage. Here, we demonstrate that the forkhead family member FoxD3 is essential for the unmethylated mark observed at the Alb1 enhancer in ES cells, with FoxA1 replacing FoxD3 following differentiation into endoderm. Up-regulation of FoxD3 and loss of CpG methylation at the Alb1 enhancer accompanied the reprogramming of mouse embryonic fibroblasts (MEFs) into induced pluripotent stem (iPS) cells. Studies of two genes expressed in specific hematopoietic lineages revealed that the establishment of enhancer marks in ES cells and iPS cells can be regulated both positively and negatively. Furthermore, the absence of a pre-established mark consistently resulted in resistance to transcriptional activation in the repressive chromatin environment that characterizes differentiated cells. These results support the hypothesis that pluripotency and successful reprogramming may be critically dependent on the marking of enhancers for many or all tissue-specific genes.

Pioneer factor interactions and unmethylated CpG dinucleotides mark silent tissue-specific enhancers in embryonic stem cells

Recent studies have suggested that, in ES cells, inactive genes encoding early developmental regulators possess bivalent histone modification domains and are therefore poised for activation. However, bivalent domains were not observed at typical tissue-specific genes. Here, we show that windows of unmethylated CpG dinucleotides and putative pioneer factor interactions mark enhancers for at least some tissue-specific genes in ES cells. The unmethylated windows expand in cells that express the gene and contract, disappear, or remain unchanged in nonexpressing tissues. However, in ES cells, they do not always coincide with common histone modifications. Genomic footprinting and chromatin immunoprecipitation demonstrated that transcription factor binding underlies the unmethylated windows at enhancers for the Ptcra and Alb1 genes. After stable integration of premethylated Ptcra enhancer constructs into the ES cell genome, the unmethylated windows readily appeared. In contrast, the premethylated constructs remained fully methylated and silent after introduction into Ptcra-expressing thymocytes. These findings provide initial functional support for a model in which pioneer factor interactions in ES cells promote the assembly of a chromatin structure that is permissive for subsequent activation, and in which differentiated tissues lack the machinery required for gene activation when these ES cell marks are absent. The enhancer marks may therefore represent important features of the pluripotent state.

Global regulation of erythroid gene expression by transcription factor GATA-1

Transcription factor GATA-1 is required for erythropoiesis, yet its full actions are unknown. We performed transcriptome analysis of G1E-ER4 cells, a GATA-1-null erythroblast line that undergoes synchronous erythroid maturation when GATA-1 activity is restored. We interrogated more than 9000 transcripts at 6 time points representing the transition from late burst forming unit-erythroid (BFU-E) to basophilic erythroblast stages. Our findings illuminate several new aspects of GATA-1 function. First, the large number of genes responding quickly to restoration of GATA-1 extends the repertoire of its potential targets. Second, many transcripts were rapidly down-regulated, highlighting the importance of GATA-1 in gene repression. Third, up-regulation of some known GATA-1 targets was delayed, suggesting that auxiliary factors are required. For example, induction of the direct GATA-1 target gene beta major globin was late and, surprisingly, required new protein synthesis. In contrast, the gene encoding Fog1, which cooperates with GATA-1 in beta globin transcription, was rapidly induced independently of protein synthesis. Guided by bioinformatic analysis, we demonstrated that selected regions of the Fog1 gene exhibit enhancer activity and in vivo occupancy by GATA-1. These findings define a regulatory loop for beta globin expression and, more generally, demonstrate how transcriptome analysis can be used to generate testable hypotheses regarding transcriptional networks.

Metabolic dysfunction and depletion of mitochondria in hearts of septic rats

Our previous studies indicate that hearts from septic rats have decreased work with oxygen wasting. The present studies test if there is energy deficit, changes in cardiac mitochondrial content and caspase activation during sepsis. Anesthetized, male Sprague-Dawley rats received no surgical treatment (control), laparotomy (sham), or laparotomy with cecal ligation and puncture (CLP) to induce polymicrobial septic shock. Hearts were isolated 12-14 h later. Cardiac work, oxygen consumption, substrate oxidation and energy stores were measured in perfused hearts. Normalized density of mitochondria was determined in ventricles without perfusion by morphometric analysis with electron microscopy. Citrate synthase activity was assessed in homogenates and isolated mitochondria. Cardiac work decreased significantly in CLP (47%), while oxygen consumption and glucose oxidation were unchanged compared with control or sham hearts (oxygen and substrate wasting). Tissue adenosine triphosphate, creatine phosphate and glycogen were lower in CLP hearts (energy deficit). Mitochondrial grid intersects decreased significantly from 151 +/- 8 sham to 130 +/- 4 CLP out of 361 possible intersects and autophagy was observed in CLP hearts. Total activity of citrate synthase decreased in homogenates (99 +/- 8 micromol/min/g wet weight sham vs. 62 +/- 7 CLP, P < 0.05) and in the mitochondrial fraction (27 +/- 1 micromol/min/g wet weight sham to 22 +/- 1 CLP, P < 0.05). Calculated mitochondrial content decreased from 63 +/- 4 mg protein/g wet weight sham to 46 +/- 5 CLP, P < 0.05 (mitochondrial depletion). Caspase-3 activity doubled and tumor necrosis factor alpha content tripled in CLP hearts. CONCLUSIONS. - Oxygen and substrate wasting in CLP occurs with fewer mitochondria and energy deficit, processes that are coincident with caspase-3 activation.

Gene expression phenotype in heterozygous carriers of ataxia telangiectasia

The defining characteristic of recessive diseases is the absence of a phenotype in the heterozygous carriers. Nonetheless, subtle manifestations may be detectable by new methods, such as expression profiling. Ataxia telangiectasia (AT) is a typical recessive disease, and individual carriers cannot be reliably identified. As a group, however, carriers of an AT disease allele have been reported to have a phenotype that distinguishes them from normal control individuals: increased radiosensitivity and risk of cancer. We show here that the phenotype is also detectable, in lymphoblastoid cells from AT carriers, as changes in expression level of many genes. The differences are manifested both in baseline expression levels and in response to ionizing radiation. Our findings show that carriers of a recessive disease may have an "expression phenotype." In the particular case of AT, this suggests a new approach to the identification of carriers and enhances understanding of their increased cancer risk. More generally, we demonstrate that genomic technologies offer the opportunity to identify and study unaffected carriers, who are hundreds of times more common than affected patients.

A model of reversible inhibitors in the gastric H+/K+-ATPase binding site determined by rotational echo double resonance NMR

Several close analogues of the noncovalent H(+)/K(+)-ATPase inhibitor SCH28080 (2-methyl-3-cyanomethyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine) have been screened for activity and examined in the pharmacological site of action by solid-state NMR spectroscopy. TMPIP, the 1,2,3-trimethyl analogue of SCH28080, and variants of TMPIP containing fluorine in the phenylmethoxy ring exhibited IC(50) values for porcine H(+)/K(+)-ATPase inhibition falling in the sub-10 microm range. Deuterium NMR spectra of a (2)H-labeled inhibitor titrated into H(+)/K(+)-ATPase membranes revealed that 80-100% of inhibitor was bound to the protein, and K(+)-competition (2)H NMR experiments confirmed that the inhibitor lay within the active site. The active binding conformation of the pentafluorophenylmethoxy analogue of TMPIP was determined from (13)C-(19)F dipolar coupling measurements using the cross-polarization magic angle spinning NMR method, REDOR. It was found that the inhibitor adopts an energetically favorable extended conformation falling between fully planar and partially bowed extremes. These findings allowed a model to be proposed for the binding of this inhibitor to H(+)/K(+)-ATPase based on the results of independent site-directed mutagenesis studies. In the model, the partially bowed inhibitor interacts with Phe(126) close to the N-terminal membrane spanning helix M1 and residues in the extracellular loop bridging membrane helices M5 and M6 and is flanked by residues in M4.

Activation of poly(ADP-ribose) polymerase in severe hemorrhagic shock and resuscitation

This study examines activation of poly(ADP-ribose) polymerase (PARP) in the ileum during hemorrhage and resuscitation and determines if inhibition of PARP reduces organ dysfunction and metabolic acidosis. Awake, nonheparinized rats were hemorrhaged (40 mmHg, 60 min). Resuscitation used Ringer's solution (2 1/3 x shed volume) and packed red blood cells (2/3 shed volume). Ileal PARP activity was elevated at the end of hemorrhage (3.6-fold) and 10 min of resuscitation (5-fold). The subsequent decline in PARP activity observed after 60 min of resuscitation was not due to cleavage by caspase-3. Ileum permeability increased 10-fold and circulating liver enzymes increased 4- to 6-fold following 60 min of resuscitation in animals pretreated with 3-aminobenzoic acid, a structural analog that does not inhibit PARP. Pretreatment with 3-aminobenzamide (3-AB), a PARP inhibitor, reduced these changes, whereas posttreatment with a bolus of 3-AB was ineffective. Metabolic acidosis, accumulation of lactate, and base deficit was reduced by pretreatment with 3-AB. PARP is activated in the ileum by hemorrhage and by resuscitation. Activation of PARP contributes to organ dysfunction in the ileum and liver and appears to be central to the development of metabolic acidosis.

Biventricular cardiac dysfunction after acute massive pulmonary embolism in the rat

Cardiac dysfunction has been documented in vivo after acute massive pulmonary embolism (AMPE). The present study tests whether intrinsic ventricular dysfunction occurs in rat hearts isolated after AMPE. AMPE was induced in spontaneously breathing ketamine-xylazine-anesthetized rats by thrombus infusion until mean arterial blood pressure (MAP) was approximately 40% of basal measurement. A hypotensive control group underwent controlled blood withdrawal to produce MAP approximately 40% of basal levels. Shams underwent identical surgical and anesthesia preparation but without pulmonary embolization. Hearts were perfused in isovolumetric mode, and simultaneous right ventricular (RV) and left ventricular (LV) pressures were measured. AMPE caused arterial hypotension with hypoxemia (PO(2) = 50 +/- 14 Torr), acidemia (pH = 7.26 +/- 0.11), and high lactate concentration (6.9 +/- 1.7 mM). Starling curves from both ventricles demonstrated that AMPE significantly reduced ex vivo systolic contractile function in the RV (P = 0.031) and LV (P = 0.008) compared with both the hypotensive control and sham hearts. AMPE did not alter coronary flow or compliance in either ventricle. Soluble tumor necrosis factor-alpha decreased in the RV (P = 0.043) and LV (P = 0.005) tissue. These data support the hypothesis that AMPE produces intrinsic biventricular dysfunction and suggest that arterial hypotension is not the principal mechanism of this dysfunction.

Role of fatty acids in the recovery of cardiac function during resuscitation from hemorrhagic shock

This study tested the hypothesis that removal of fatty acids as a fuel source would improve cardiac efficiency at the expense of reduced cardiac contractile function in the isolated working heart after hemorrhage-retransfusion. Non-heparinized male Sprague-Dawley rats were anesthetized with ketamine-xylazine and were hemorrhaged to a mean arterial blood pressure of 40 mmHg for 1 h. Two-thirds volume of shed blood was reinfused together with 0.9% NaCl in a volume equal to 2.3 times the shed blood volume, followed by continuous infusion of 0.9% NaCl at 10 mL/kg per h for 3 h. Hearts were removed and perfused in closed, recirculating working mode for 60 min to measure hydraulic work and cardiac efficiency. Rates of glycolysis and glucose oxidation were assessed with [5-3H/U-14C] glucose (11 mM) in the absence or presence of 0.4 mM palmitate. Compared to baseline measurements, hemorrhage-retransfusion significantly reduced arterial blood glucose (228+/-7 versus 118+/-12 mg/dL) and non-esterified fatty acid concentrations (0.36+/-0.01 versus 0.30+/-0.02 mM), while elevating blood lactate (0.8+/-0.1 versus 2.5+/-0.4 mM). Perfusion of sham hearts with glucose-only did not alter cardiac work compared to shams perfused with glucose plus palmitate. However, shocked hearts perfused with glucose-only demonstrated a significant reduction in cardiac work compared to shocked hearts perfused with glucose plus palmitate and compared to sham hearts perfused with glucose only (P < 0.05, repeated measures ANOVA). Shocked hearts perfused with glucose plus palmitate showed no reduction in cardiac work compared to shams. Shocked hearts perfused with glucose-only had increased glucose oxidation rates compared to shams perfused with glucose plus palmitate. In sham hearts perfused with glucose-only, myocardial glycogen and triacylglycerol contents were significantly reduced compared to hearts freeze-clamped in situ. These endogenous fuels were not decreased in shocked hearts. These data indicate that hemorrhagic shock renders the heart unable to mobilize endogenous fuels, and suggest that withdrawal of fatty acid oxidation will impair myocardial energy metabolism during resuscitation.

Dynamics and orientation of N+(CD3)3-bromoacetylcholine bound to its binding site on the nicotinic acetylcholine receptor

Dynamic and structural information has been obtained for an analogue of acetylcholine while bound to the agonist binding site on the nicotinic acetylcholine receptor (nAcChoR), using wide-line deuterium solid-state NMR. Analysis of the deuterium lineshape obtained at various temperatures from unoriented nAcChoR membranes labeled with deuterated bromoacetylcholine (BAC) showed that the quaternary ammonium group of the ligand is well constrained within the agonist binding site when compared with the dynamics observed in the crystalline solids. This motional restriction would suggest that a high degree of complementarity exists between the quaternary ammonium group of the ligand and the protein within the agonist binding site. nAcChoR membranes were uniaxially oriented by isopotential centrifugation as determined by phosphorous NMR of the membrane phospholipids. Analysis of the deuterium NMR lineshape of these oriented membranes enriched with the nAcChoR labeled with N(+)(CD(3))(3)-BAC has enabled us to determine that the angle formed between the quaternary ammonium group of the BAC and the membrane normal is 42 degrees in the desensitized form of the receptor. This measurement allows us to orient in part the bound ligand within the proposed receptor binding site.

Lactate improves cardiac efficiency after hemorrhagic shock

This study was undertaken to examine the role of lactate on cardiac function and metabolism after severe acute hemorrhagic shock. Anesthetized, nonheparinized rats were bled to a mean arterial pressure of 25-30 mm Hg for 1 h; controls were not bled. Their hearts were removed, and cardiac work and efficiency (work/oxygen consumption) were measured in the isolated working heart mode for 60 min. The hearts were perfused with one of five substrate combinations: 1) glucose (11 mM), 2) glucose + 0.4 mM palmitate, 3) glucose + 0.4 mM palmitate + 8.0 mM lactate, 4) glucose + 1.2 mM palmitate, or 5) glucose + 1.2 mM palmitate + 8.0 mM lactate. After perfusion, hearts were freeze-clamped, and tissue contents of free coenzyme-A (CoA), acetyl CoA, and succinyl CoA were measured, as was myocardial pyruvate dehydrogenase (PDH) activity. The addition of 8.0 mM lactate significantly improved cardiac work in shocked hearts perfused with 0.4 mM palmitate and increased cardiac efficiency in the presence of either 0.4 mM or 1.2 mM palmitate. Compared to control hearts, shocked hearts exhibited a 20-30% decrease in PDH activity. Shocked hearts perfused with lactate demonstrated no increase in acetyl CoA content but did have a significant increase in tissue succinyl CoA compared to control hearts perfused with lactate or shocked hearts perfused without lactate. In the heart recovering from severe hemorrhagic shock, lactate improves cardiac efficiency in the presence of free fatty acids, possibly by a anaplerosis of the tricarboxylic acid cycle.

Depletion of lactate by dichloroacetate reduces cardiac efficiency after hemorrhagic shock

We have demonstrated previously that dichloroacetate (DCA) treatment in rodents ameliorates, via activation of the pyruvate dehydrogenase complex, the cardiovascular depression observed after hemorrhagic shock. To explore the mechanism of this effect, we administered DCA in a large animal model of hemorrhagic shock. Mongrel hounds were anesthetized with 1.5% isoflurane and were measured for hemodynamics, myocardial contractility, and myocardial substrate utilization. They were hemorrhaged to a mean arterial pressure of 35 mm Hg for 90 min or until arterial lactate levels reached 7.0 mM (1137 +/- 47 mL or 49 +/- 2% total blood volume). Animals were chosen at random to receive DCA dissolved in water or an equal volume of saline at the onset of resuscitation. Two-thirds of the shed blood volume was returned immediately after giving an equivalent volume of saline. Two hours after the onset of resuscitation, mean arterial pressure was not different between DCA and control groups (79 +/- 3 vs. 82 +/- 3 mm Hg, respectively). Arterial lactate levels were significantly reduced by DCA (0.5 +/- 0.06 vs. 2.0 +/- 0.2 mM). However, DCA treatment was associated with a decreased stroke volume index (0.56 +/- 0.06 vs. 0.82 +/- 0.08 mL/kg/beat) and a decreased myocardial efficiency (19 vs. 41 L x mm Hg/mL/100 g tissue). During resuscitation by DCA, myocardial lactate consumption was reduced (21.4 +/- 3.7 vs. 70.7 +/- 16.3 micromole/min/100 g tissue) despite a three-fold increase in myocardial pyruvate dehydrogenase activity, while free fatty acid levels actually began to rise. Although increased lactate oxidation should be beneficial during resuscitation, we propose that DCA treatment led to a deprivation of myocardial lactate supply, which reduced net myocardial lactate oxidation, thus compromising myocardial function during resuscitation from hemorrhagic shock.

Nonanticoagulant heparin inhibits NF-kappaB activation and attenuates myocardial reperfusion injury

Heparin reduces ischemia-reperfusion injury to myocardium. This effect has been attributed to complement inhibition, but heparin also has other activities that might diminish ischemia-reperfusion. To further probe these mechanisms, we compared heparin or an o-desulfated nonanticoagulant heparin with greatly reduced anticomplement activity. When given at the time of coronary artery reperfusion in a canine model of myocardial infarction, heparin or o-desulfated heparin equally reduced neutrophil adherence to ischemic-reperfused coronary artery endothelium, influx of neutrophils into ischemic-reperfused myocardium, myocardial necrosis, and release of creatine kinase into plasma. Heparin or o-desulfated heparin also prevented dysfunction of endothelial-dependent coronary relaxation following ischemic injury. In addition, heparin and o-desulfated heparin inhibited translocation of the transcription nuclear factor-kappaB (NF-kappaB) from the cytoplasm to the nucleus in human endothelial cells and decreased NF-kappaB DNA binding in human endothelium and ischemic-reperfused rat myocardium. Thus heparin and nonanticoagulant heparin decrease ischemia-reperfusion injury by disrupting multiple levels of the inflammatory cascade, including the novel observation that heparins inhibit activation of the proinflammatory transcription factor NF-kappaB.

Heart function after severe hemorrhagic shock

OBJECTIVE

Test whether brief deep hemorrhagic hypotension or prolonged moderate hemorrhagic hypotension impairs intrinsic heart function.

METHODS

Pentobarbital-anesthetized, non-anticoagulated rats were cannulated via the carotid artery. This study focuses on three main groups: 1) hemorrhage to a mean arterial blood pressure (MAP)=25 mm Hg for 1 h (1 h severe shock), 2) hemorrhage to MAP=40 mm Hg for 3 h (3 h moderate shock), 3) no hemorrhage (control). Hearts were either freeze-clamped in-situ for tissue analysis (n=6 per group) or were removed to study in vitro cardiac function and efficiency using a working heart perfusion (n=12 per group, glucose (11 mM)/palmitate (0.4 mM), 3% BSA buffer). Following perfusion, hearts were freeze-clamped and analyzed for free CoA, acetyl-, succinyl-, and malonyl-CoA, ATP content and for TNF-alpha content.

RESULTS

Isolated working hearts obtained following 1 h of severe shock generated 20% less hydraulic work than hearts obtained from control rats or rats subjected to 3 h of moderate shock. The cardiac efficiency (work/O2 consumption) was also significantly reduced with 1 h severe shock (0.76 +/- 0.07 after 15 min perfusion) versus control (0.96 +/- 0.06) or 3 h prolonged shock (1.10 +/- 0.09). Myocardial Co-A ester, ATP and TNF-alpha concentrations were not different between control and shocked hearts, although TNF-alpha concentrations increased significantly in all hearts during ex vivo perfusion.

CONCLUSIONS

Depth of hypotension is more important than duration in causing intrinsic cardiac dysfunction. This post-hemorrhagic cardiac dysfunction is not a result of substrate limitation to the heart, nor myocardial TNF-alpha accumulation, but is more likely a result of impaired transfer of energy from molecular oxygen into external cardiac work.

A comparison of resuscitation with packed red blood cells and whole blood following hemorrhagic shock in canines

Resuscitation with crystalloid and packed red blood cells has for the most part replaced the use of plasma and whole blood in the initial treatment of hemorrhagic shock. The effects of such changes on cardiovascular function following hemorrhagic shock remain largely unexplored. We examined cardiovascular function in anesthetized canines subjected to severe hemorrhagic shock. Mongrel canines of either gender were anesthetized with isoflurane and instrumented for measurement of arterial pressure, cardiac output, coronary flow, and left ventricular pressure and volume for the determination of end systolic elastance (Ees). Following a 30-min stabilization period, blood was rapidly removed to induce fixed pressure (mean arterial pressure = 35 mmHg) hemorrhagic shock for 90 min or until an arterial lactate of 7.0 mM was achieved. Animals were then resuscitated with 2/3 of the shed volume as lactated Ringer's and an equal volume of either whole blood (WB, n = 8) or packed red blood cells (PRBC, n = 10) resuspended in lactated Ringer's (LR) solution to replace expressed plasma volume. PRBC resuscitated dogs showed lower values of mean arterial pressure, cardiac output, rates of ventricular contraction and relaxation and myocardial work. Increasing the maintenance infusion rate of LR (10 mL/kg/h) following PRBC infusion normalized mean arterial pressure, but not other indices of cardiovascular function. Thus, WB, but not PRBC resuscitation restores normal myocardial function during resuscitation from severe hemorrhagic shock.

Inhibition of poly(ADP-ribose) synthetase improves vascular contractile responses following trauma-hemorrhage and resuscitation

Hyporeactivity of vessels to constrictor agents is thought to contribute to cardiovascular decompensation following trauma-hemorrhage and resuscitation. In this study, we determined if inhibition of poly(ADP-ribose) synthetase (PARS) activity prevented the development of vascular hyporeactivity in rats following trauma-hemorrhage and resuscitation. Trauma consisted of a laparotomy that was closed and rats were hemorrhaged into a reservoir containing citrate to 40 mm Hg for 90 min. Resuscitation included 2/3 of the shed blood plus 2 1/3 of the shed volume as Ringer's lactate. Sham animals received the laparotomy and were time-matched. Induction of iNOS was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Aortic rings isolated 6 h after the initiation of hemorrhage (4.5 h after resuscitation) showed decreased responsiveness to norepinephrine (peak developed tension 0.31+/-0.01 g/mg tissue) compared with sham rings (0.43+/-0.02 g/mg tissue), but no change in EC50 for this response (approximately 5x10(-8) M). Addition of the PARS inhibitor, 3-aminobenzamide, at the onset of resuscitation prevented the decrease in response of aortic rings. The addition of the structural analogue, 3-aminobenzoic acid, which does not inhibit PARS, did not prevent the decrease in vascular reactivity. These agents did not alter vascular responses to norepinephrine in sham animals. iNOS induction was not associated with depressed contractile function. These results indicate that decreased vascular reactivity was prevented by inhibition of PARS and that PARS activation was independent of iNOS induction following trauma-hemorrhage and resuscitation.

Trace amounts of albumin protect against ischemia and reperfusion injury in isolated rat hearts

Albumin is used to provide colloid osmotic pressure in some resuscitation and organ preservation protocols. These solutions are expensive and carry the risks of using high concentrations of blood products. Used as a carrier of drugs and substrates, the concentration of albumin present in perfusates may be considerably lower in experimental ischemia. The present study examined if trace amounts of albumin (0.0004%) reduce injury from ischemia and reperfusion in isolated rat hearts. Hearts were perfused by the Langendorff technique (60 mmHg) with an intraventricular balloon. Zero-flow ischemia (20 min, 37 degrees C) was followed by reperfusion (35 min, 37 degrees C). Recovery of contractile function during reperfusion was significantly improved by the presence of fatty acid-free bovine serum albumin (BSA) (22 290+/-1280 mmHg/min, pressure-rate product) or rat serum albumin (RSA) (21 095+/-2836 mmHg/min) compared with Krebs-Henseleit buffer with no albumin (KHB) (9660+/-2324 mmHg/min). Release of lactate dehydrogenase activity, formation of tissue edema and accumulation of tissue malonyldialdehyde were significantly reduced in hearts receiving BSA or RSA compared with KHB alone. These parameters were not altered by the presence of albumin in non-ischemic control hearts or in the pre-ischemic values of the hearts subjected to ischemia and reperfusion. Development of ischemic contracture with an extended period of ischemia (27 min) was not altered by the presence of BSA, suggesting that protection observed with albumin occurred during reperfusion, rather than during ischemia. Reperfusion following 45 min of ischemia with bovine serum albumin resulted in similar myocardial injury to hearts that were reperfused following 20 min of ischemia without bovine serum albumin. Thus, trace amounts of albumin provide significant reduction in myocardial injury from ischemia and reperfusion, probably via antioxidant mechanisms.

Effects of citrated whole blood transfusion in response to hemorrhage

BACKGROUND AND PURPOSE

Standard treatment for massive hemorrhage in dogs is infusion of whole blood or of packed red blood cells with fresh frozen plasma if whole blood is not available. Although most whole blood is collected using a citrate-based anticoagulant, knowledge of citrate's relevant non-anticoagulant effects is not widespread. Citrate's anticoagulant activity is achieved through chelation of divalent metal cations (e.g., magnesium, calcium), which may exacerbate cardiovascular and metabolic insults attributable to hemorrhage.

METHODS

Blood pressures, gas tensions, metabolites, and electrolytes; myocardial metabolites, pressures, and contractility; cardiac output; and left cranial descending and circumflex coronary artery flows were measured in 21 anesthetized dogs after hemorrhage was induced by collection of blood into a citrated reservoir to mean arterial pressure of 45 mm Hg for approximately 60 min (until arterial lactate concentration was 7.0 mmol/L), followed by a 1-h transfusion and 2 h of maintenance.

RESULTS

Arterial ionized calcium concentration, total peripheral resistance, and myocardial function decreased significantly during hemorrhage. All aforementioned responses but myocardial function continued to decrease during the initial 20 min of transfusion, then began to recover. Total peripheral resistance and end-systolic elastance were the only factors significantly related to calcium concentration.

CONCLUSION

Transfusion with citrated whole blood may significantly alter calcium concentration, negatively affecting myocardial and vascular function.

Iron-mediated cardiotoxicity develops independently of extracellular hydroxyl radicals in isolated rat hearts

BACKGROUND

Myocardial iron toxicity is often attributed to free radical damage. Present studies examine the role of extracellular hydroxyl radical formation in this process.

METHODS

In vitro reactions examined the rate of hydroxyl radical formation using salicylate trapping with high-pressure liquid chromatography separation and electrochemical detection of 2,3- and 2,5- dihydroxybenzoic acid. Isolated rat hearts were perfused by the Langendorff technique under the same buffer conditions to determine changes in myocardial contractility, release of tissue lactate dehydrogenase activity, and formation of lipid peroxidation products when iron was added to the perfusate with or without the formation of extracellular radicals.

RESULTS

In vitro reactions, performed in Krebs buffer alone or with addition of iron (25 microM), produced levels of hydroxyl radicals that were nondetectable with salicylate trapping. Addition of iron/ascorbate (FeSO4 = 25 microM, ascorbate = 1 mM), or iron/ascorbate/histidine (FeSO4 = 25 microM, ascorbate = 1 mM, histidine = 15 mM) produced significant and equivalent accumulation of hydroxyl radicals. Isolated rat hearts were perfused under the same 4 conditions. Control heart contractile function was stable with little release of lactate dehydrogenase activity and low levels of thiobarbituric acid reactive substances (TBARS). There was significant and equal injury to contractile function, release of lactate dehydrogenase activity, and accumulation of TBARS in hearts in the presence (iron/ascorbate) and absence (iron alone) of extracellular hydroxyl radicals. In addition, there was significant reduction in injury with iron/ascorbate/histidine, where the formation of extracellular hydroxyl radicals was equal to those observed with iron/ascorbate alone. Additional control hearts, perfused with histidine alone, showed stable heart function.

CONCLUSIONS

These findings indicate that the extracellular formation of hydroxyl radicals is not responsible for iron-mediated cardiotoxicity.

Large-pore hemodialysis in acute endotoxin shock

OBJECTIVE

This study was undertaken to test the hypothesis that hemodialysis with a large-pore membrane would improve heart function during acute endotoxin shock.

SETTING

Large animal laboratory.

DESIGN

Eighteen mongrel dogs were instrumented to measure left ventricular maximum end-systolic elastance (left ventricular maximum elastance at end systole), cardiac output, circumflex artery blood flow, and myocardial mechanical efficiency (CO x MAP/MVO2, where CO is cardiac output, MAP is mean arterial pressure, and MVO2 is myocardial oxygen consumption). Plasma catecholamine concentrations were determined by high-performance liquid chromatography. Endotoxin shock was induced by infusing 5.0 microg/kg/min of Escherichia col 0127:B8 endotoxin in the portal vein for 60 mins, followed by 2.0 microg/kg/min of constant infusion. Control dogs (n = 6) received 4.0 mL/kg/min of saline; hemodialysis dogs (n = 6) underwent venovenous hemodialysis in 50-min intervals using a polysulfone filter (1.2 m2; mean pore size, 0.50 nm; blood flow rate, 400 mL/min; ultrafiltrate, "zero-balanced"); shams (n = 5) were treated identically to hemodialysis dogs, except that no convective dialysis was performed. A fourth group (n = 6) was treated with dopamine (5.0-7.0 microg/kg/min, optimal dose for contractile increase based on dose-response studies).

MEASUREMENTS AND MAIN RESULTS

After 2 hrs of treatment, left ventricular maximum elastance at end systole increased and was unchanged in controls (30 +/- 5 mm Hg/mm) and shams (24 +/- 6 mm Hg/mm) compared with basal control. Hemodialysis treatment increased contractility (53 +/- 4 mm Hg/mm), as did dopamine treatment (54 +/- 7 mm Hg/mm). Endotoxin shock reduced mechanical efficiency to 45% of basal control; with hemodialysis treatment, left ventricular efficiency returned to 64% of basal control measurement, compared with 49% with dopamine treatment. During treatment, myocardial glucose uptake was increased with hemodialysis compared with other groups. No difference was observed among groups for left ventricular end-diastolic pressures or dimensions, or catecholamine concentrations.

CONCLUSIONS

Large-pore hemodialysis increased left ventricular contractility to a similar degree as dopamine and provided a marginal improvement in myocardial glucose uptake and mechanical efficiency.

Mechanisms of Ca2+ antagonism in imipramine-induced toxicity of isolated adult rat cardiomyocytes

Classic explanations of cyclic antidepressant toxicity often focus on Na+ channel blockade; however, cyclic antidepressant toxicity often causes decreased myocardial contractile function. The present experiments first examine inhibition of cytosolic Ca2+ signals by imipramine. Second, the experiments test if alkalinization prevents the inhibition of Ca2+ signals. Cardiomyocytes from adult rat hearts were loaded with fura-2 dye, and intracellular calcium, [Ca2+]i, was quantified using ratio fluorescence techniques. Changes in [Ca2+]I were induced by electrical pacing, depolarization with KCl (84 mM), or treatment with caffeine (10 mM). Imipramine (10-30 microM) inhibited [Ca2+]i transients in electrically paced cardiomyocytes. Imipramine (7.5-30 microM) also inhibited Ca2+ signals in KCl depolarized cells. These inhibitory effects were similar to those observed with nisoldipine (100-2000 nM), a selective L-channel blocker. The rise in [Ca2+]i that was triggered with caffeine (10 mM) was not significantly changed by imipramine (30 microM). Inhibition of KCl-induced Ca2+ signals by imipramine was prevented by alkalinization of the medium (tris(hydroxymethyl)aminomethane, pH 7.6), but not by elevation of extracellular sodium to 170 mM. Alkalinization was effective in the presence of HOE642, a selective Na+/H+ (NHE) subtype 1 inhibitor. These data show that imipramine causes Ca2+ antagonism in heart cells which is independent of sarcoplasmic reticulum Ca2+, and that alkaline treatment prevents this Ca2+ antagonism rather than stimulating an alternate source of Ca2+ via Na+/H+ and subsequent Na+/Ca2+ exchange.

Macroscopic orientation of natural and model membranes for structural studies

One approach for obtaining high-resolution structural and functional information for biomembranes and their proteins is by static solid-state NMR of oriented systems. Here, a general procedure to align fully functional biological membranes containing large membrane proteins (Mr >30,000) is described. The method, based on the isopotential spin-dry ultracentrifugation technique, relies on the centrifugation of membrane fragments onto a support with simultaneous, or subsequent, partial evaporation of the solvent which aids alignment. The quality of orientation, as shown by the mosaic spread of the samples, was monitored by static solid-state 31P NMR for the phospholipids and by 2H NMR for a deuterated retinal in bovine rhodopsin. The generality of this method is demonstrated with three different membranes containing bovine rhodopsin in reconstituted bilayers, natural membranes with the red cell anion exchange transport protein in erythrocytes, band 3, and the nicotinic acetylcholine receptor.

Activation of pyruvate dehydrogenase improves heart function and metabolism after hemorrhagic shock

This study was designed to test the hypothesis that activation of myocardial pyruvate dehydrogenase (PDH) would improve recovery of heart function after brief, severe hemorrhagic shock. Pentobarbital-anesthetized rats were instrumented to monitor arterial blood pressure and right ventricular pressures. Rats were hemorrhaged via femoral artery to 25-30 mmHg mean arterial pressure (MAP) for 60 min, followed by retransfusion of shed blood with either 1.0 cc saline with no dichloroacetate (-DCA) or 1.0 cc saline containing 150 mg/kg sodium dichloroacetate (+DCA). Rats were observed for 3 h after retransfusion. Hearts were freeze-clamped in situ for analysis of adenosine triphosphate (ATP), creatine phosphate (CrP), lactate and pyruvate content as well as PDH activity (PDHa) and total PDH activity (PDHt). Three h after retransfusion, the rate pressure product (RPP=HRxPSP) was 23 000+/-2733 with no DCA treatment v 36 2769 mmHg/min with DCA treatment (P<0.05, ANOVA). Treatment with DCA also increased myocardial tissue content of high energy phosphates (ATP=10.1+/-1.1 and CrP=5.8+/-1.0 micromol/g weight-DCA, v 15.1+/-0.9 and 14.7+/-1.0 micromol/g dry weight+DCA, P<0.05, both measurements). DCA administration also significantly reduced myocardial lactate contents (14.6+/-2.7 micromol/g dry weight-DCA v 5.9+/-1.0+DCA). Hemorrhagic shock did not change PDHa or PDHt compared to hearts obtained during the pre-hemorrhage period. Retransfusion with DCA significantly increased PDHa activity (6.8+/-1.1 micromol/g dry weight/min-DCA v 29.7+/-2.0 micromol/g dry weight/min+DCA). PDHt was not different between controls and DCA-treated groups. These data indicate that activation of myocardial PDH by adding DCA to retransfused blood improved heart function and metabolism after severe hemorrhagic shock.

The diabetogenic effects of acute verapamil poisoning

Verapamil poisoning is known to produce hyperglycemia and metabolic acidosis in humans. The purpose of this study was to elucidate mechanisms of verapamil-induced hyperglycemia in awake dogs. Mongrel canines were chronically instrumented to permit studies in the conscious state. In six healthy dogs, steady-state glucose infusion requirement after 1 hr of insulin infusion at 1000 mU/min was 19 +/- 1 mg/kg/min. In six separate dogs, verapamil toxicity was induced via verapamil infusion in the portal vein; during verapamil toxicity, the glucose infusion requirement with an insulin infusion rate of 1000 mU/min was significantly decreased (3 +/- 1 mg/kg/min; p < 0.05, unpaired t test). Eleven other verapamil-toxic dogs were also treated with either saline (n = 6, 3.0 ml/kg/hr) or glucagon (n = 5, 10 microg/kg/min). Insulin concentrations were not changed vs basal concentrations in either group. Catecholamine concentrations increased at least 15-fold in all groups (from 458 +/- 169 to 6973 +/- 480 pg/L in the saline-treated group). Glucose concentrations increased in saline-treated animals from 3.7 +/- 0.3 to 11.2 +/- 1.0 micromol/L, and with glucagon treatment, increased from 3.3 +/- 0.3 to 16.1 +/- 1.6 micromol/L (p < 0.05 vs saline, ANOVA). Verapamil poisoning appears to produce hyperglycemia by inducing systemic insulin resistance, blocking insulin release, together with an intact stress hormone response and glucogenic capacity.

Insulin improves heart function and metabolism during non-ischemic cardiogenic shock in awake canines

OBJECTIVES

This study was undertaken to examine in-situ heart function and metabolism during insulin treatment of verapamil-induced cardiogenic shock in awake canines.

METHODS

Twenty mongrel canines were instrumented to monitor myocardial substrate uptakes (glucose, lactate, free fatty acids, oxygen [MVO2]), as well as ventricular (LV) end-systolic elastance (Emax), LV efficiency (LV minute work/MVO2), and Tau. Shock was induced by graded intraportal verapamil infusion followed by randomized assignment to one of 4 treatment groups: saline control (3.0 ml/kg/min, n = 5), epinephrine (5 micrograms/kg/min, n = 5), glucagon (10 micrograms/kg/min, n = 5) or insulin (1000 mU/min, n = 5) with dextrose to clamp arterial [glucose] +/- 10% of basal concentrations.

RESULTS

Insulin treatment significantly increased Emax (34 +/- 3 vs. 17 +/- 3 mmHg/mm, saline control), and shortened Tau (9 +/- 3 ms) compared to saline control (42 +/- 5 ms), epinephrine (20 +/- 4 ms) and glucagon (35 +/- 8 ms). With insulin treatment, mechanical efficiency increased to 20,097 +/- 2070 vs. 12,424 +/- 1615 mmHg.mm/ml/O2/100 g in controls. Simultaneously, insulin increased myocardial lactate uptake (35 +/- 2 vs. 17 +/- 4 mumol/min/100 g. saline control), but did not increase glucose uptake. Epinephrine and glucagon decreased mechanical efficiency compared to saline controls, coincident with increased myocardial fatty acid consumption, but without increasing lactate uptake. One dog died early with glucagon treatment before the first death in the saline-treated group.

CONCLUSIONS

Insulin improves systolic and diastolic heart function during aerobic shock and accelerates in-vivo myocardial lactate oxidation.

Effect of ethanol, haloperidol, and lorazepam on cardiac conduction and contraction

Haloperidol and lorazepam are commonly used to sedate ethanol (E)-intoxicated patients in emergency departments. This study was conducted to explore the role of ethanol in altering the potency of haloperidol and lorazepam with respect to cardiac conduction and contraction. For mechanical studies, isolated rat hearts were studied under isovolumetric conditions by using standard Langendorff technique. Hearts were perfused with Krebs-Heinseleit-Bicarbonate buffer containing haloperidol or lorazepam in concentrations ranging from 100 to 750 ng/ml (one heart per drug concentration). For both haloperidol and lorazepam individually, significant reductions in Left ventricular-generated pressure (LVGP) were observed at a concentration of 750 ng/ml (haloperidol = 2,250 nM and lorazepam = 2,000 nM). The addition of 20 and 65 mM ethanol shifted the concentration-response effect of haloperidol such that LVGP was significantly reduced at haloperidol = 500 and 300 ng/ml, respectively (p < 0.05 vs. basal control; paired t test). Ethanol produced no observable shift on the lorazepam concentration-response for LVGP. For electrophysiologic studies, hearts were perfused with haloperidol and lorazepam (300 ng/ml) +/- 65 mM ethanol. Compared with basal control, E + H significantly decreased heart rate (-74 +/- 12 beats/min) and increased His-ventricular conduction time (+7.6 +/- 1.5 ms vs. +1.7 +/- 0.6 ms for control hearts). Both haloperidol and EH significantly increased atrioventricular (AV) effective refractory period and the atrioventricular-His (AH) conduction interval. No significant changes in any electrophysiologic parameter were observed with ethanol or lorazepam perfused individually or with the combination of ethanol and lorazepam. Ethanol potentiates haloperidol-induced electromechanical depression of isolated rat hearts. Ethanol had no such effect on lorazepam.

Myocardial metabolism during graded intraportal verapamil infusion in awake dogs

Verapamil produces comparatively greater in vivo left ventricular (LV) depression than other calcium channel antagonists produce, possibly because of myocardial metabolic derangements in addition to L-channel antagonism. Therefore, we studied myocardial lipid and carbohydrate usage and the effect of insulin treatment during progressive verapamil toxicity. Verapamil was infused through the portal vein to simulate oral overdose. Eighteen mongrel dogs were instrumented to measure multiple hemodynamic and metabolic parameters. After 1-week recovery, dogs underwent control euglycemic insulin dose-response studies (n = 6) in the conscious state: at 1,000 mU/mm insulin infusion rate, myocardial glucose and lactate extraction increased seven- and threefold, respectively with no change in coronary artery blood flow or ventricular elasticity and end-systole (Ees). In 12 separate dogs, intraportal graded verapamil toxicity was induced in 3 h by increasing the infusion rate hourly: 0.04 -- 0.08 -- 0.1 mg/kg/mm. At the end of hour 3, myocardial extraction of free fatty acids decreased from 33 +/- 4 to 9 +/- 3% (mean +/- SEM, p < 0.05), without significant change in myocardial blood flow or arterial free fatty acid concentration. Verapamil toxicity increased arterial glucose from 3.5 +/- 0.16 to 6.1 +/- 1.1 mM; simultaneously, myocardial glucose extraction doubled, although endogenous insulin concentrations did not increase. Arterial lactate concentrations and net myocardial lactate uptake both increased (p < 0.05 vs basal blue). Ees decreased from 28 +/- 1 mm Hg/mm (basal) to 20 +/- 2 mm Hg/mm (end of hour 3, p <0.05). Animals were randomized into two treatment groups; either (a) insulin-glucose (1,000 mU/mm, n 6; arterial glucose was clamped +/- 10% with 50% dextrose), or (b) saline controls (n = 6) that received equivalent volume of saline. After 1-h insulin treatment, Ees increased to 34 + 3 mm Hg; in controls, Ees was 15 +/- 3 mm Hg/mm (p < 0.05). With insulin-glucose treatment, neither myocardial glucose nor lactate extraction increased significantly (p = 0.06 for lactate). Verapamil therefore inhibits myocardial fatty acid uptake and impedes insulin-stimulated myocardial glucose uptake; under these conditions, insulin-glucose treatment increases myocardial contractile function independent of increased sugar transport. These findings indicate that verapamil toxicity produces myocardial insulin resistance and, potentially, nutrient deprivation that may contribute to clinically relevant negative inotropy.

Antioxidant properties of dihydropyridines in isolated rat hearts

Isolated Sprague-Dawley rat hearts were perfused under constant flow conditions. Hearts were treated with vehicle or treatment buffers, including nisoldipine, nifedipine, or the optical isomers (+)- or (-)-nisoldipine. H2O2 (500-600 microM) was then added to the treatment buffer for 12 min. H2O2 was removed and perfusion continued with treatment buffers (10 min) followed by control buffer (20 min). Contractile function decreased following perfusion with H2O2. Contractile function was protected was protected in a concentration-dependent manner (nisoldipine=19,26,50,63 and 78%; nifedipine = 23, 37, 55,61, and 63% of pre-peroxide function, 0, 0.1, 0.5 1.0, and 5 microliter, respectively). There were no significant differences between equal concentrations of nisoldipine and nifedipine. Contractile function was equally protected by both (+)- and (-)-nisoldipine compared with vehicle-treated hearts (56, 67, and 16%, of pre-peroxide function, respectively). Biochemical analyses indicated that H2O2 damaged plasma membranes (increased lactate dehydrogenase leak) and caused lipid peroxidation (elevated tissue thiobarbituric acid reactive substances). Biochemical changes were equally reduced by nisoldipine and nifedipine treatments and by (+)- and (-)-nisoldipine. The treatment groups have widely differing IC50 values as calcium channel antagonists, yet they had equal effects in reducing oxidative injury, suggesting that this beneficial effect is not mediated by calcium antagonism.

Antioxidant effects of pyruvate in isolated rat hearts

Sprague-Dawley rat hearts were perfused under constant flow conditions, and a balloon was inserted into the left ventricle to measure heart rate (HR) and left ventricular pressures. Left ventricular generated pressure (LVGP) was calculated as peak systolic minus end diastolic pressure. Three substrate groups, pyruvate (5 mM), glucose (15 mM) and octanoate (0.5 mM), were employed. Oxidative stress was induced by perfusion with tertiary-butyl hydroperoxide (tBHP, 0.35 mM, 12 min) followed by 25 min of perfusion with control buffer. Hearts perfused with pyruvate showed no significant decrease in contractile function following tBHP treatment (HR x LVGP = 17666 +/- 585 mmHg/min, initial: 16414 +/- 2083 post-tBHP treatment). Glucose-perfused hearts had an intermediate decrease in function (19174 +/- 828 mmHg/min, initial; 4379 +/- 2083 post-tBHP), while octanoate-perfused hearts recovered no contractile function. Peak release of LDH was lowest in hearts perfused with pyruvate (115 +/- 17 mU/g wet wt/min), intermediate in glucose-perfused hearts (1575 +/- 380) and highest in octanoate-perfused hearts (3074 +/- 499). Thiobarbituric acid reactive substances (TBARS) were unchanged in hearts perfused with pyruvate (16.2 +/- 5 nmoles/g wet wt), but increased significantly in glucose-perfused hearts (36.1 +/- 1) and in octanoate-perfused hearts (45.5 +/- 9). Total glutathione levels were unchanged in hearts perfused with pyruvate (753 +/- 68 nmoles/g wet wt), but significantly decreased in glucose-perfused hearts (594 +/- 68) and in octanoate-perfused hearts (445 +/- 38) following tBHP-treatment. Pyruvate significantly reduced oxidative injury. In contrast, glucose provided a small reduction in injury while octanoate-perfused hearts had the most severe injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nisoldipine upon endothelial dysfunction following ischaemic and peroxidative injury in the perfused rat heart

OBJECTIVE

Previous studies showed that treatment of hearts with nisoldipine improves recovery of cardiac function following ischaemia, improves reperfusion, and reduces the constrictor sensitivity to endothelin. The aim of the present study was to assess the reduction in vasodilator responses that occurs following ischaemia and reperfusion or after oxidative stress, and to determine whether nisoldipine treatment improves these dilator responses.

METHODS

Isolated perfused rat hearts were studied. Coronary vessels were constricted by the addition of U46619 and dilator responses were determined with the addition of acetylcholine (endothelium dependent) or glyceryl trinitrate (endothelium independent). Responses were compared before and after low flow ischaemia (20%, 30 min) and reperfusion (30 min), or treatment with tert-butyl hydroperoxide (tBHP) (0.9 mM, 12 min, 30 min wash).

RESULTS

The addition of U46619 caused a prolonged increase in perfusion pressure of 50 to 70 mm Hg which was not significantly different before and after treatment. Dilatation responses to acetylcholine were significantly reduced following ischaemia and reperfusion (34% of preischaemic values) or tBHP (47.6% of pre-tBHP values), while responses to glyceryl trinitrate were not significantly changed. In contrast, when hearts were perfused with nisoldipine, the responses to acetylcholine were significantly improved (88% of preischaemic values with 5 nM nisoldipine, and 68% to 78% of pre-tBHP values with 0.5 nM to 5 nM nisoldipine). Responses to acetylcholine following tBHP were not significantly improved when hearts were perfused with verapamil (5 nM 43.5%, 5 microM 32%, of pre-tBHP values), or diltiazem (5 nM 37%, 5 microM 31%, of pre-tBHP values).

CONCLUSIONS

Ischaemia and reperfusion or oxidative stress reduced endothelium dependent responses, but not endothelium independent responses. Nisoldipine reduced the injury to endothelial cell function associated with ischaemia and reperfusion or oxidative stress.

Reversal of hypotension induced by Vibrio vulnificus lipopolysaccharide in the rat by inhibition of nitric oxide synthase

Intravenous infusion of Vibrio vulnificus lipopolysaccharide (LPS) (1 mg/kg body wt) in rats caused a dramatic drop in mean arterial pressure within 10 min and a further decline in mean arterial pressure and heart rate which lead to death between 25 and 70 min. Rats treated with LPS followed 10 min later by the intravenous infusion of NG-monomethyl-L-arginine (L-NMMA, 20 mg/kg body wt) showed an initial drop in mean arterial pressure owing to the LPS infusion, followed by a transient rise in mean arterial pressure which lasted for approximately 40 min after the infusion of L-NMMA. The pressure values then remained level for at least 150 min post-LPS infusion. Control rats treated with equivalent volumes of saline infusion showed stable values of mean arterial pressure and heart rate. Additional control rats receiving L-NMMA alone showed the transient rise in mean arterial pressure, followed by a return to the baseline values. The results indicate that the symptoms of endotoxic shock resulting from V. vulnificus LPS may result in part from the stimulation of the activity of nitric oxide synthase. Inhibition of nitric oxide synthase by L-NMMA is a possible treatment for toxic shock induced by V. vulnificus.

Effects of nisoldipine upon vasoconstrictor responses and binding of endothelin-1 in ischemic and reperfused rat hearts

Changes in the vascular response of isolated, perfused rat hearts to endothelin-1 (ET-1) and binding of [125I]ET-1 to cardiac membranes were examined following ischemia (30 min, zero flow) and reperfusion (15 min). Infusion of ET-1 (0, 2.5, 5, 7.5, and 10 x 10(-10) M) increased the control heart perfusion pressure (61, 73, 88, 102, and 117 mm Hg, respectively). Ischemic and reperfused hearts were more sensitive to ET-1 infusion (p less than 0.05 at all concentrations). Nisoldipine (NIS, 1 nM) prevented the rise in sensitivity to ET-1 following ischemia and reperfusion. Two binding sites for [125I]ET-1 were identified in cardiac membranes. High-affinity (Kd = 0.04 nM, Bmax = 0.46 pmol/mg of protein) and low-affinity (Kd = 13.8 nM, Bmax = 5.4 pmol/mg of protein) sites were unchanged by ischemia and reperfusion, and NIS did not change binding constants in control or ischemic and reperfused hearts. Increased ET-1 sensitivity after ischemia may be due to other factors. Endothelium-dependent vasodilation and endothelium-independent vasodilation were significantly reduced following 30 min of ischemia. Inhibition of dilator responses may account for increased ET-1 responses following transient ischemia.

Discordant effects of nisoldipine on coronary vascular resistance and permeability changes during reflow after ischemia in isolated rabbit hearts

Effects of a low dose (5 nM) of nisoldipine on vascular and ventricular function were assessed in isolated rabbit hearts during 2 h of reperfusion after 40 min of global, zero-flow ischemia. External detection of bolus injections of 125I-BSA and pressure data generated during the experiment provided repeated estimates of albumin permeation and vascular hemodynamics (resistance, vascular volume, and fractional rate of intravascular washout of 125I-BSA (k01]. In control hearts perfused continuously for 3.5 h, vascular resistance, vascular volume, LVEDP, and k01 remained constant, while maximum +dP/dt and -dP/dt increased 25% above baseline values, and estimates of albumin permeation increased 1.7 x baseline. Addition of 5 nM nisoldipine to the perfusate after the baseline period produced sustained decreases in vascular resistance (16% vs mean baseline value) without significantly affecting any other parameter. Postischemic perfusion of hearts increased vascular resistance and vascular volume approximately 50% above baseline, decreased k01 by 25% (intravascular washout of 125I-BSA was prolonged), and increased albumin permeation approximately 5 x baseline. While LVEDP remained elevated 3 x baseline, maximum +dP/dt and -dP/dt recovered 100% of baseline values (75-80% of untreated control values at comparable time points). Addition of 5 nM nisoldipine to the perfusate prior to ischemia prevented the increased vascular resistance during reflow, prevented the decrease in k01 and the increase in vascular volume, but did not affect the increased albumin permeation and, in general, did not affect the rate of recovery of left ventricle function. These results indicate that a low dose of nisoldipine preserves postischemic coronary vascular hemodynamics, but has little or no effect on the increased vascular leakage of albumin.

Effects of nisoldipine on the no-reflow phenomenon in globally ischemic rat hearts

Isolated working rat hearts, receiving no drug treatment, recovered low values of contractile function after 33 min of zero-flow global ischemia and 30-min reperfusion, had lower ATP and creatine phosphate (CrP) values in the subendocardium than in the subepicardium after reperfusion (subendocardial/subepicardial ratio ATP = 0.44, CrP = 0.45), and had a subendocardial reperfusion defect including 15.9% of ventricular cross-sectional area. Contracture pressure increased during the later part of ischemia to 25.4 mm Hg. Addition of nisoldipine (1 nM) 10 min before ischemia did not depress preischemic contractile function and did not delay or reduce contracture or the breakdown of high-energy phosphate compounds during ischemia. On reperfusion, nisoldipine-treated hearts showed a dramatic improvement in recovery of contractile function, increased subendocardial energy levels yielding a more uniform transmural energy distribution (subendocardial/subepicardial ratio ATP = 0.79, CrP = 0.94), and enhanced reflow to the subendocardium (area of no reflow = 1.0%). In contrast, addition of vehicle or a low concentration of verapamil (1 nM) before ischemia or nisoldipine during reperfusion did not improve recovery of contractile function. The beneficial effects do not appear to be induced by direct myocardial actions of nisoldipine but may reflect improved vascular function which is associated with the vascular selectivity of this calcium antagonist.

Correlation between cytosolic free calcium, contracture, ATP, and irreversible ischemic injury in perfused rat heart

The relations between ATP depletion, increased cytosolic free calcium concentration [( Cai]), contracture development, and lethal myocardial ischemic injury, as evaluated by enzyme release, were examined using 19F nuclear magnetic resonance to measure [Cai] in 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5F-BAPTA)-loaded perfused rat hearts. Total ischemia at 37 degrees C was induced in beating hearts, potassium-arrested hearts, magnesium-arrested hearts, and hearts pretreated with 0.9 microM diltiazem to reduce but not abolish contractility. In the beating hearts, time-averaged [Cai], which is intermediate between the systolic and the basal [Cai], was 544 +/- 74 nM. In contrast, in the potassium- and magnesium-arrested hearts, the time-averaged values are lower than in beating hearts (352 +/- 88 nM for potassium arrest, 143 +/- 22 nM for magnesium arrest). During ischemia, ATP depletion, contracture, and a rise in [Cai] are delayed by cardiac arrest, but all occur more rapidly in the potassium-arrested hearts than in the magnesium-arrested hearts. The diltiazem-treated hearts were generally similar to the magnesium-arrested hearts in their response to ischemia. Under all conditions, contracture development was initiated after tissue ATP had fallen to less than 50% of control; invariably, there was a progressive rise in [Cai] during and following contracture development. Reperfusion with oxygenated perfusate shortly after peak contracture development resulted in a return of [Cai] to its preischemic level, resynthesis of creatine phosphate, no significant enzyme release, and no substantial loss of 5F-BAPTA from the heart. The data demonstrate that an increase in [Cai] precedes lethal myocardial ischemic injury. This rise in [Cai] may accelerate the depletion of cellular ATP and may directly contribute to the development of lethal ischemic cell injury.

Effects of diltiazem on lactate, ATP, and cytosolic free calcium levels in ischemic hearts

Changes in tissue lactate, ATP, and cytosolic free calcium (Cai) were examined in isolated, perfused rat hearts receiving 20 min of zero-flow global ischemia (37 degrees C). Addition of diltiazem before ischemia caused a concentration-dependent decrease in lactate accumulation. This effect was not mediated by modulation of norepinephrine release since depletion of catecholamines by reserpine did not alter lactate accumulation, and diltiazem treatment reduced lactate accumulation in catecholamine-depleted hearts. Diltiazem-treated hearts showed a concentration-dependent decrease in tissue ATP utilization that was associated with the decrease in tissue lactate during ischemia. Basal time averaged Cai, determined by fluorine NMR using 5FBAPTA, was 620 nM. Diltiazem (0.9 microM) decreased this value to 489 nM and reduced heart rate and maximum pressure developed (81.3 and 53.9% of control, respectively) before ischemia. Cai increased fourfold between 9 and 15 min of ischemia in hearts receiving no drug, while there was no increase in Cai in diltiazem-treated hearts. These results show that diltiazem reduces the use of ATP and therefore production of lactate during ischemia, and indicate a relationship between preservation of ATP and maintenance of Cai that may be important in the beneficial effects of diltiazem during myocardial ischemia.

A low concentration of nisoldipine reduces ischemic heart injury: enhanced reflow and recovery of contractile function without energy preservation during ischemia

Isolated working rat hearts which received no drug treatment had reduced ATP and creatine phosphate levels and increased lactate content during 20 min of ischemia. When subjected to 33 min of ischemia and 30 min of reperfusion, these hearts recovered low values of cardiac output (9.8 ml/min), heart rate, maximum developed pressure, pressure-rate product (72.9, 32.6, 27.5% of control, respectively), had low levels of tissue ATP, and reduced coronary flow upon reperfusion. Addition of nisoldipine (1 nM) 10 min before ischemia caused no decrease in cardiac output or heart rate, slightly decreased maximum developed pressure and pressure-rate product (93% of control), and did not reduce the degradation of ATP and creatine phosphate or the accumulation of lactate during 20 min of ischemia. When nisoldipine was included 10 min before ischemia, during ischemia (33 min) and reperfusion (30 min), however, the recovery of cardiac function and tissue ATP levels was significantly increased. This protective effect occurred when drug treated ischemic hearts were reperfused with control buffer, indicating residual effects. The beneficial effects of nisoldipine were not due to changes in afterload or preload (isolated perfused heart), collateral flow (zero flow model), energy preservation during ischemia (little contractile depression, ATP not enhanced during ischemia), or reduced lactate accumulation during ischemia. The beneficial effects were associated with increased coronary flow (31% higher than no drug) during reperfusion, indicating a reduction in the no-reflow phenomenon.