Nonenzymatic separation of myocardial cell nuclei from whole heart tissue

Effect of Gestational Intake of Fisetin (3,3',4',7-Tetrahydroxyflavone) on Developmental Methyl Mercury Neurotoxicity in F1 Generation Rats

Methyl mercury (MeHg) is a developmental neurotoxin that causes irreversible cognitive damage in offspring of gestationally exposed mothers. Currently, no preventive drugs are established against MeHg developmental neurotoxicity. The neuroprotective effect of gestational administration of a flavanoid against in utero toxicity of MeHg is not explored much. Hence, the present study validated the effect of a bioactive flavanoid, fisetin, on MeHg developmental neurotoxicity outcomes in rat offspring at postnatal weaning age. Pregnant Wistar rats were simultaneously given MeHg (1.5 mg/kg b.w.) and two doses of fisetin (10 and 50 mg/kg b.w. in two separate groups) orally from gestational day (GD) 5 till parturition. Accordingly, after parturition, on postnatal day (PND) 24, weaning F₁ generation rats were studied for motor and cognitive behavioural changes. Biochemical and histopathological changes were also studied in the cerebral cortex, cerebellum and hippocampus on PND 25. Administration of fisetin during pregnancy prevented behavioural impairment due to transplacental MeHg exposure in weaning rats. Fisetin decreased the levels of oxidative stress markers, increased enzymatic and non-enzymatic antioxidant levels and increased the activity of membrane-bound ATPases and cholinergic function in F₁ generation rats. In light microscopic studies, fisetin treatment protected the specific offspring brain regions from significant morphological aberrations. Between the two doses of fisetin studied, 10 mg/kg b.w. was found to be more satisfactory and effective than 50 mg/kg b.w. The present study shows that intake of fisetin during pregnancy in rats ameliorated in utero MeHg exposure-induced neurotoxicity outcomes in postnatal weaning F₁ generation rats.

Effect of Ethanol Exposure on Slow Wave Activity and Smooth Muscle Contraction in the Rat Small Intestine

BACKGROUND

Ethanol ingestion causes a variety of gastrointestinal disturbances including motility alterations. Slow wave propagation coordinates gastrointestinal motility, and abnormal slow wave activity is thought to contribute to motility disorders. To date, however, little is known about the effect of acute ethanol on motility disturbances associated with slow wave activity.

AIM

To investigate the effect of ethanol on small intestine slow wave activity.

METHODS

Segments (3-5 cm long) were isolated from the rat duodenum, jejunum, and ileum and mounted in an organ bath superfused with a normal Tyrode solution or with 1, 3, or 5% ethanol containing Tyrode. The electrical activities were recorded using an array of 121 extracellular electrodes, and motility recordings were performed using a digital video camera.

RESULTS

The frequency and amplitude of slow wave activity were not altered at 1, 3, or 5% ethanol concentrations, but a significant drop in velocity was found at 3 and 5% ethanol. Furthermore, inexcitable areas appeared in a dose-dependent manner. Slow wave was sometimes also seen to propagate in a circular fashion, thereby describing a reentrant loop. Finally, in all duodenal, jejunal, and ileal segments, ethanol inhibited contractions and became fully quiescent at 3-5%.

CONCLUSIONS

These studies for the first time demonstrate that ethanol significantly inhibits slow wave and spike activity in a dose-dependent manner and could also initiate reentrant activities. Intestinal contractions were also inhibited in a dose-dependent manner. In conclusion, ethanol inhibits both slow wave activity and motor activity to cause ethanol-induced intestinal disturbances.

Rationale for early treatment of polycystic kidney disease

In hereditary cystic disorders, renal injury begins with the formation of the first cyst. Renal injury may manifest as large kidneys, abdominal pain, hypertension and hematuria in children and young adults with autosomal dominant polycystic kidney disease (ADPKD). In autosomal recessive PKD (ARPKD) and ADPKD, cysts form primarily in collecting ducts and expand progressively. Collecting duct cysts that block urine flow have the potential to block urine formation in large numbers of upstream nephrons. In an ARPKD rat congenitally lacking vasopressin, only a few cysts developed until exogenous arginine vasopressin (AVP) was administered. AVP elevates cyclic AMP in vulnerable tubule cells to stimulate mitogenesis and fluid secretion, thereby causing cysts to form and enlarge indefinitely. The administration of an AVP-V2 receptor inhibitor or the consumption of sufficient water to persistently lower plasma AVP levels will ameliorate disease progression. Renal volume measurements provide the most reliable way to forecast long-term outcome in individual children and adult patients with ADPKD. Many drugs that have demonstrated efficacy in small clinical trials, preclinical trials and cell-based studies are in the treatment pipeline. Counseling, regular exercise, limitation of dietary calories, salt, protein and fat, increased fluid intake throughout the day and treatment of hypertension are components of a rational treatment program that can be offered at an early age to those with, or at risk for developing PKD.

Cross-talk between calcineurin/NFAT and Jak/STAT signalling induces cardioprotective alphaB-crystallin gene expression in response to hypertrophic stimuli

Among the stress proteins that are up-regulated in the heart due to imposed biomechanical stress, αB-crystallin (CryAB) is the most abundant and pivotal in rendering protection against stress-induced cell damage. Cardiomyocyte-specific expression of the CryAB gene was shown to be dependent upon an intact αBE4 cis-element located in the CryAB enhancer. To date, there is no evidence on the identity of regulatory proteins and associated signalling molecules that control CryAB expression in cardiomyocytes. In this study, we define a mechanism by which the calcineurin/NFAT and Jak/STAT pathways regulate CryAB gene expression in response to a hypertrophic agonist endothelin-1 (En-1), in hypertrophic hearts of mice with pressure overload (TAC) and in heart-targeted calcineurin over-expressing mice (MHC-CnA). We observed that in response to various hypertrophic stimuli the transcription factors NFAT, Nished and STAT3 form a dynamic ternary complex and interact with the αBE4 promoter element of the CryAB gene. Both dominant negative NFAT and AG490, an inhibitor of the Jak2 phosphorylation, inhibited CryAB gene transcription in transient transfection assays. AG490 was also effective in blocking the nuclear translocation of NFAT and STAT3 in cardiomyocytes treated with En-1. We observed a marked increase in CryAB gene expression in MHC-CnA mouse hearts accompanied with increased phosphorylation of STAT3. We conclude that hypertrophy-dependent CryAB gene expression can be attributed to a functional linkage between the Jak/STAT and calcineurin/NFAT signalling pathways, each of which are otherwise known to be involved independently in the deleterious outcome in cardiac hypertrophy.

A mathematical model of the proton balance in the outer mantle epithelium of Anodonta cygnea L

In the freshwater mollusc Anodonta cygnea and other unionids, the mantle plays an important role in the regulation of the movements of ions between the shell and the extrapaleal fluid. In this report, a mathematical model that attempts to describe the cell metabolic mechanisms underlying the operation of the outer mantle epithelium as a source of protons is presented. We encoded the information gathered by studying the epithelium in vitro, which includes the electrophysiology of the preparation, measurements of basic rates of transport of protons and base, the effect of metabolic and transport inhibitors on its electrical behavior and the dynamic measurements of pHi. The model was conceived so that the short-circuit current (Isc) and fluxes of Na+, K+ and Cl(-); intracellular volume; electrical potential; and ionic concentrations can be computed as a function of time. Furthermore, the analytical descriptions of all ionic fluxes involved are such that the effect of transport inhibitors can be simulated. In all the simulations performed, it was possible to reproduce the experimental results obtained with specific inhibitors of transport systems on the Isc and on pHi. In some cases, it was necessary to make alterations to one or more parameters of the reference condition. For each simulation carried out, the analysis of the results was consistent. The model is an analytical tool that can be used to show the internal coherence of the qualitative model previously proposed and to plan further experiments.

Myocardial lipidomics. Developments in myocardial nuclear lipidomics

The development of electrospray ionization mass spectrometry has been critical for the analyses of lipidomes from subcellular organelles. The myocardial nuclear lipidome likely has a key role in the molecular regulation of gene expression. In fact, recent studies have suggested that specific phospholipid classes bind and regulate specific transcription factors. The dynamic regulation of the myocardial nuclear lipidome may be critical in mediating long-term pathological responses to stresses such as ischemia, tachycardia, and hypertension. In this brief review, the preparation of myocardial nuclei is discussed, and the resulting nuclear lipidome from rat and rabbit are shown as examples. The rabbit myocardial nuclear lipidome contains relatively more plasmenylcholine/phosphatidylcholine molecular species in comparison to that ratio observed in the rat myocardial nuclear lipidome. The composition of the rat myocardial nuclear choline glycerophospholipid pool was relatively enriched with molecular species containing arachidonic acid and docosahexaenoic acid in comparison to that in the rabbit myocardial nuclear choline glycerophospholipid pool. While the ethanolamine glycerophospholipids of the rabbit myocardial nuclei are enriched with arachidonic acid and plasmalogens, the ethanolamine glycerophospholipid profile from rat myocardial nuclei show less plasmalogen and more species containing docosahexaenoic acid. Last, significant differences in the ethanolamine glycerophospholipid molecular species were observed in the rabbit heart lipidomes from the nucleus and the mitochondria. Quantitation of these lipid species in hearts subjected to pathophysiological stresses may provide important information on the role of the myocardial nuclear lipidome on long-term cardiac cell function.

Peripheral pacemakers and patterns of slow wave propagation in the canine small intestine in vivo

In an anesthetized, open-abdomen, canine model, the propagation pattern of the slow wave and its direction, velocity, amplitude, and frequency were investigated in the small intestine of 8 dogs. Electrical recordings were made using a 240-electrode array from 5 different sites, spanning the length of the small intestine. The majority of slow waves propagated uniformly and aborally (84%). In several cases, however, other patterns were found including propagation in the oral direction (11%) and propagation block (2%). In addition, in 69 cases (3%), a slow wave was initiated at a local site beneath the electrode array. Such peripheral pacemakers were found throughout the entire intestine. The frequency, velocity, and amplitude of slow waves were highest in the duodenum and gradually declined along the intestine reaching lowest values in the distal ileum (from 17.4+/-1.7 c/min to 12.2+/-0.7 c/min; 10.5+/-2.4 cm/s to 0.8+/-0.2 cm/s, and 1.20+/-0.35 mV to 0.31+/-0.10 mV, respectively; all p<0.001). Consequently, the wavelength of the slow wave was strongly reduced from 36.4+/-0.8 cm to 3.7 +/- 0.1 cm (p<0.001). We conclude that the patterns of slow wave propagation are usually, though not always, uniform in the canine small intestine and that the gradient in the wavelength will influence the patterns of local contractions.

Effects of Gap Geometry on Conduction Through Discontinuous Radiofrequency Lesions

Background— Gaps of sufficient cross-sectional dimensions within linear radiofrequency (RF) lesions may allow conduction through the lesion. The purpose of this study was to examine the effects of different gap geometries on conduction through discontinuous RF lesions.

Methods and Results— Radiofrequency lesions were created in isolated, perfused rabbit right ventricular (RV) free wall preparations to produce gaps with 3 different lesion geometries: straight, bifurcated, and angled (n=10 each group). Angled preparations contained 2 right angles within the conduction path. Optical mapping was used to assess bidirectional conduction through the myocardium before and after gap formation during pacing at 1000-, 400-, and 200-ms cycle lengths. Histological analysis was performed on each preparation after optical mapping. After lesion formation, 9 of 10 straight gap preparations and 1 of 10 angled gap preparations demonstrated bidirectional conduction ( P <0.001) at all cycle lengths. Nine of 10 bifurcated gap preparations demonstrated bidirectional conduction and 1 demonstrated unidirectional conduction at all cycle lengths. Two bifurcated gap preparations showed rate-dependent unidirectional 2:1 conduction. All unidirectional and rate-dependent block occurred during impulse propagation in the direction of diverging arms of the bifurcation. The occurrence of bidirectional conduction in the gaps was associated with the gap geometry ( P <0.0001). Histological analysis confirmed the continuity of viable myocardium transmurally throughout the length of the gap in each preparation. The sites of conduction block were demonstrated to be just after the first angle in the conduction path for angled gaps and at the branch point of a bifurcated gap. The predominant myofiber orientation was changed relative to the conduction path at angulations of the gaps. Flecainide (0.1 μmol/L) produced bidirectional conduction block in straight and bifurcated gap preparations with bidirectional conduction at baseline.

Conclusions— Conduction through discontinuities in RF lesions is associated with gap geometry. Complex gap geometry may allow for unidirectional and/or rate-dependent block. Gaps within RF lesions are susceptible to pharmacological blockade.

Amiloride derivatives enhance insulin release in pancreatic islets from diabetic mice

BACKGROUND

Amiloride derivatives, commonly used for their diuretic and antihypertensive properties, can also cause a sustained but reversible decrease of intracellular pH (pHi). Using dimethyl amiloride (DMA) on normal rodent pancreatic islets, we previously demonstrated the critical influence of islet pHi on insulin secretion. Nutrient-stimulated insulin secretion (NSIS) requires a specific pHi-range, and is dramatically enhanced by forced intracellular acidification with DMA. Furthermore, DMA can enable certain non-secretagogues to stimulate insulin secretion, and induce time-dependent potentiation (TDP) of insulin release in mouse islets where this function is normally absent. The present study was performed to determine whether pHi-manipulation could correct the secretory defect in islets isolated from mice with type 2 diabetes.

METHODS

Using two mouse models of type 2 diabetes, we compared a) pHi-regulation, and b) NSIS with and without treatment with amiloride derivatives, in islets isolated from diabetic mice and wild type mice.

RESULTS

A majority of the islets from the diabetic mice showed a slightly elevated basal pHi and/or poor recovery from acid/base load. DMA treatment produced a significant increase of NSIS in islets from the diabetic models. DMA also enabled glucose to induce TDP in the islets from diabetic mice, albeit to a lesser degree than in normal islets.

CONCLUSION

Islets from diabetic mice show some mis-regulation of intracellular pH, and their secretory capacity is consistently enhanced by DMA/amiloride. Thus, amiloride derivatives show promise as potential therapeutic agents for type 2 diabetes.

Reconstruction of the patterns of gene expression in the developing mouse heart reveals an architectural arrangement that facilitates the understanding of atrial malformations and arrhythmias

Firm knowledge about the formation of the atrial components and of the variations seen in congenital cardiac malformations and abnormal atrial rhythms is fundamental to our understanding of the normal structure of the definitive atrial chambers. The atrial region is relatively inaccessible and has continued to be the source of disagreement. Seeking to resolve these controversies, we made three-dimensional reconstructions of the myocardial components of the developing atrium, identifying domains on the basis of differential expression of myocardial markers, connexin40, and natriuretic precursor peptide A. These reconstructions, made from serial sections of mouse embryos, show that from the outset of atrial development, the systemic and pulmonary veins are directly connected to the atrium. Relative to the systemic junctions, however, the pulmonary venous junction appears later. Our experience shows that three-dimensional reconstructions have three advantages. First, they provide clear access to the combined morphological and molecular data, allowing clarification and verification of morphogenetic concepts for nonmorphological experts and setting the scene for further discussion. Second, they demonstrate that, from the outset, the myocardium surrounding the pulmonary veins is distinct from that clothing the systemic venoatrial junctions. Third, they reveal an anatomical and molecular continuity between the entrance of the systemic venous tributaries, the internodal atrial myocardium, and the atrioventricular region. All these regions are derived from primary myocardium, providing a molecular basis for the observed nonrandom distribution of focal right atrial tachycardias.

Depletion of PKD1 by an antisense oligodeoxynucleotide induces premature G1/S-phase transition

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the growth of epithelial cells and the influx of cyst fluid. The 14-kb mRNA of the polycystic kidney disease gene, PKD1, encodes the polycystin-1 protein, whose function remains unknown. In this study, we observed that polycystin-1 localized in epithelial cell-cell contacts of 293 cells. We found, by bromodeoxyuridine (BrdU) incorporation experiments and Western blot analysis of S-phase-specific cyclins, that the depletion of polycystin-1 led to an increased cell proliferation rate and caused a premature G1/S-phase transition. In addition, we showed that the depletion of polycystin-1 reduced the amount of p53 in 293 cells irradiated by UV light, suggesting that polycystin-1 acts as a regulator of G1 checkpoint, which controls entry into the S phase and prevents the replication of damaged DNA. Our results might provide an insight into the formation and progression of ADPKD cysts.

Effects of cholinergic m-receptor agonists on insulin release in islets from obese and lean mice of different ages: the importance of bicarbonate

OBJECTIVES

Decreased beta-cell function is often observed in older individuals and may predispose to the development of type 2 diabetes. We have studied the age-related effects of M-receptor agonism on insulin release in islets isolated from female ob/ ob and lean mice.

METHODS

Islets were challenged with 11.1 or 16.7 mmol/L glucose in media with HCO3/CO2 (KRBH) or without (KRH).

RESULTS

Acetylcholine (ACh) (10 micromol/L) increased glucose-induced insulin release in islets from 4- to 5-week-old ob/ob mice both in KRBH and KRH. In islets from 9- to 13-month-old ob/ob mice, 10 micromol/L ACh and 10 micromol/L carbachol enhanced insulin release in KRBH but not in KRH. ACh increased insulin release in islets from 4- to 5-week-old and 16-month-old lean mice incubated in KRH but not in islets from 24-month-old lean mice. The Na/H exchange inhibitor dimethylamiloride (100 micromol/L) did not affect insulin release stimulated by M-receptor agonists. Carbachol did not enhance glucose-induced insulin secretion in islets from 9- to 10-month-old ob/ob mice in the presence of low extracellular Na concentration. ACh stimulated cytoplasmic Ca mobilization in islets from 9- to 10-month-old mice also when bicarbonate was omitted. The results suggest that cholinergic signal transduction involving extracellular bicarbonate and Na is reduced with age in mouse pancreatic islets.

CONCLUSION

Chronic hyperglycemia may add to the age-related decrease in M-receptor-mediated insulin release by affecting the buffering capacity of the islets through mechanisms other than amiloride-sensitive proton exchange.

Ligand-mediated decrease of thyroid hormone receptor-alpha1 in cardiomyocytes by proteosome-dependent degradation and altered mRNA stability

Tri-iodo-L-thyronine (T3) is essential for maintaining normal cardiac contractile function by regulating transcription of numerous T3-responsive genes. Both hormone availability and relative amounts of nuclear thyroid hormone receptor isoforms (TRalpha1, TRbeta1) determine T3 effectiveness. Cultured neonatal rat ventricular myocytes grown in T3-depleted medium expressed predominantly TRalpha1 protein, but within 4 h of T3 treatment, TRbeta1 protein increased significantly, whereas TRalpha1 was decreased by 46 +/- 5%. Using replication-defective adenoviruses to overexpress TRalpha1 in cardiomyocytes, we studied the mechanisms by which T3 mediated the decrease in TRalpha1 protein. Inhibitors of the proteosome pathway resulted in an accumulation of ubiquitylated TRalpha1 in the nucleus and prevented T3-induced degradation of ubiquitylated TRalpha1, suggesting that T3 induced proteosome-mediated degradation of TRalpha1; however, TR ubiquitylation was T3 independent. TRalpha1 transcriptional activity, measured using transient transfection of a thyroid hormone-responsive element (TRE) reporter plasmid, was T3 dose dependent and inversely proportional to nuclear TRalpha1 content, with 10 nM T3 having maximum effect. Quantitative RT-PCR showed that both endogenous and adenovirus-expressed TRalpha1 mRNAs were significantly decreased to 54 +/- 11 and 25 +/- 5%, respectively, within 4 h of T3 treatment. Measurements of TRalpha1 mRNA half-life in actinomycin D-treated cardiomyocytes showed that T3 treatment significantly decreased TRalpha1 mRNA half-life from 4 h to less than 2 h, whereas it had no effect of TRbeta1 mRNA half-life. These data support a role for both the proteosome degradation pathway and altered mRNA stability in T3-induced decrease of nuclear TRalpha1 in the cardiomyocyte and provide novel cellular targets for therapeutic development.

Mechanisms Underlying Conduction Slowing and Arrhythmogenesis in Nonischemic Dilated Cardiomyopathy

Heart Failure (HF) is associated with an increased risk of sudden death caused by ventricular tachyarrhythmias. Recent studies have implicated repolarization abnormalities and, in particular, exaggerated heterogeneity of transmural repolarization in the genesis of polymorphic ventricular tachycardia in a canine model of nonischemic dilated cardiomyopathy. The presence and degree to which conduction abnormalities play a role in arrhythmogenesis in this model are uncertain. HF was produced in dogs by rapid RV-pacing for 3 to 4 weeks. High-resolution optical action potentials were recorded from epicardial and endocardial surfaces of arterially perfused canine wedge preparations isolated from LV and RV of normal and failing dogs. Cellular and molecular determinants of conduction were investigated using patch-clamp recordings, Western blot analysis, and immunocytochemistry. HF was associated with marked prolongation (by 33%) of the QRS duration of the volume conducted electrocardiogram and significant (>20%) slowing of epicardial and endocardial conduction velocities (CV) in both LV and RV. Cx43 expression was reduced by >40% in epicardial and endocardial layers of the LV, but was unchanged in the RV of failing hearts. Despite greater epicardial than endocardial Cx43 expression, epicardial CV was consistently slower ( P <0.01). Immunocytochemical analysis revealed predominant colocalization of Cx43 with N-cadherin in normal versus failing samples, because Cx43 was redistributed from the intercalated disk to lateral cell borders in failing tissue. Moreover, a significant ( P <0.05) increase in hypophosphorylated Cx43 was detected in the LV and RV of failing hearts. Action potential upstroke velocities in isolated ventricular myocytes from normal and failing hearts were not different ( P =0.8, not significant), and Masson trichrome staining revealed no significant change in fibrosis content in HF. Nonischemic dilated cardiomyopathy is associated with significant slowing of CV that was not directly related to reduced Cx43 expression. Changes in phosphorylation and localization of Cx43 may contribute to gap-junction dysfunction, CV slowing, and arrhythmias in HF.

Nutrient-stimulated insulin secretion in mouse islets is critically dependent on intracellular pH

BACKGROUND: Many mechanistic steps underlying nutrient-stimulated insulin secretion (NSIS) are poorly understood. The influence of intracellular pH (pHi) on insulin secretion is widely documented, and can be used as an investigative tool. This study demonstrates previously unknown effects of pHi-alteration on insulin secretion in mouse islets, which may be utilized to correct defects in insulin secretion. METHODS: Different components of insulin secretion in mouse islets were monitored in the presence and absence of forced changes in pHi. The parameters measured included time-dependent potentiation of insulin secretion by glucose, and direct insulin secretion by different mitochondrial and non-mitochondrial secretagogues. Islet pHi was altered using amiloride, removal of medium Cl-, and changing medium pH. Resulting changes in islet pHi were monitored by confocal microscopy using a pH-sensitive fluorescent indicator. To investigate the underlying mechanisms of the effects of pHi-alteration, cellular NAD(P)H levels were measured using two-photon excitation microscopy (TPEM). Data were analyzed using Student's t test. RESULTS: Time-dependent potentiation, a function normally absent in mouse islets, can be unmasked by a forced decrease in pHi. The optimal range of pHi for NSIS is 6.4-6.8. Bringing islet pHi to this range enhances insulin secretion by all mitochondrial fuels tested, reverses the inhibition of glucose-stimulated insulin secretion (GSIS) by mitochondrial inhibitors, and is associated with increased levels of cellular NAD(P)H. CONCLUSIONS: Pharmacological alteration of pHi is a potential means to correct the secretory defect in non-insulin dependent diabetes mellitus (NIDDM), since forcing islet pHi to the optimal range enhances NSIS and induces secretory functions that are normally absent.

Controversies concerning the anatomical definition of the conduction tissues

Conduction across the atrioventricular junctions had long been controversial, with arguments raging as to whether such conduction was myogenic or neurogenic. The landmark study of Tawara in 1906 established the existence of an axis of histologically specialized myocardial cells contained within fibrous sheaths as being responsible for rapid conduction from the atrial to the ventricular myocardium. Keith and Flack then demonstrated that the atrial impulse was generated in the sinus node, with subsequent slowing within the atrioventricular node of Tawara. The detailed reviews of Aschoff and Monckeberg then emphasized the morphological features that permit unequivocal recognition of the nodes, along with rapidly conducting tracts. It is now pertinent that we remember these original criteria for anatomical recognition as we discuss the steps involved in the development of these conducting structures from their embryologic primordiums. In this review, we restate the criteria of Aschoff and Monckeberg, then discuss their relevance to the developmental issues, emphasizing that all myocardial cells have the potential to conduct. The important issues, therefore, are the changes that occur as the heart itself changes from a solitary muscular tube, already possessing the capacity t generate an electrocardiogram, to the four-chambered structure we recognize in postnatal life.

On-pump coronary artery bypass surgery activates human myocardial NF-kappaB and increases TNF-alpha in the heart

PURPOSE

Myocardial tumor necrosis factor alpha (TNF) production and nuclear factor kappa B (NF-kappaB) activation has been demonstrated in chronic heart failure and experimental models of acute ischemia-reperfusion injury. Further, a cause and effect relationship has been established between these events and cardiomyocyte apoptosis following such conditions. It remains unknown, however, whether the myocardial injury associated with coronary artery bypass surgery (CAB) results in myocardial NF-kappaB activation and TNF production. We hypothesized that CAB with cardiopulmonary bypass ("on-pump") activates human myocardial NF-kappaB and increases TNF in the heart.

METHODS

Patients, 18 to 65 years of age, scheduled for elective cardiac surgery but without other preexisting disease were considered eligible for the study. Biopsies of human myocardium were obtained before and after cardiopulmonary bypass and myocardial TNF levels were determined by ELISA and cytotoxicity assay, and NF-kappaB activation was determined by electrophoretic mobility shift assay (n = 6 patients). NF-kappaB activation was quantitated with gel densitometry.

RESULTS

The clinical characteristics of the study patients were as follows (means +/- SEM): mean age (y) 50.0 +/- 5.7, male 6 (100%), cardiopulmonary bypass time (min) 107 +/- 37.7, cross-clamp time (min) 68 +/- 17.6, number of CAB 3.0 +/- 1.1, and length of hospital stay (d) 4.8 +/- 0.9. Before CAB, myocardial TNF-alpha levels were 251 +/- 22 pg/g and 33 +/- 9 U/g, as determined by ELISA and cytotoxicity assay, respectively. Following CAB, human myocardial TNF-alpha levels increased to 892 +/- 71 pg/g (P = 0.0008) and 141 +/- 11 U/g (P = 0.0042), as determined by ELISA and cytotoxicity assay, respectively. Before CAB, the ratio of bound to unbound NF-kappaB DNA was 0.009 +/- 0.0007 and after CAB the ratio was 0.24 +/- 0.01 (P < 0.0001).

CONCLUSIONS

This study represents the initial demonstration that coronary artery bypass grafting results in an activation of NF-kappaB and an increase of TNF in the heart.

Triiodothyronine-mediated myosin heavy chain gene transcription in the heart

We developed an RT-PCR assay to study both the time course and the mechanism for the triiodothyronine (T(3))-induced transcription of the alpha- and beta-myosin heavy chain (MHC) genes in vivo on the basis of the quantity of specific heterogeneous nuclear RNA (hnRNA). The temporal relationship of changes in transcriptional activity to the amount of alpha-MHC mRNA and the coordinated regulation of transcription of more than one gene in response to T(3) are demonstrated here for the first time. Quantitation of alpha-MHC hnRNA demonstrated that T(3) induced alpha-MHC transcription in hypothyroid rats within 30 min of a single injection of T(3) (0.5 microg/100 g body wt). Maximal transcription rates (135% +/- 15.8 of euthyroid values) occurred 6 h after injection and subsequently declined in parallel with serum T(3) levels. The transcription of beta-MHC was reduced to 86% of peak hypothyroid levels 6 h after a single T(3) injection and reached a nadir of 59% of hypothyroid levels at 36 h. Analysis of the time course of T(3)-mediated induction of alpha-MHC hnRNA and repression of beta-MHC hnRNA indicates that separate molecular mechanisms are involved in the coordinated regulation of these genes.

Hsp70 attenuates hypoxia/reoxygenation-induced activation of poly(ADP-ribose) synthetase in the nucleus of adult rat cardiomyocytes

Effects of heat shock protein 70 (Hsp70) translocated to nuclear fraction on hypoxia/reoxygenation injury was examined by using adult cardiomyocytes isolated from rats. Cardiomyocytes were exposed to heat shock at 42 degrees C for 15 min (HS group), and then incubated at 37 degrees C for 6-24 h. Hsp70 production increased and the protein translocated from cytosol to nucleus. The maximum level of Hsp70 in the nuclear fraction was observed 12 h after HS. When cardiomyocytes without exposure to HS (nHS group) were subjected to 120 min hypoxia/15 min reoxygenation (Hypo/Reoxy), post-hypoxic cell viability was approximately 25% of the pre-hypoxic value. A rise in poly(ADP-ribose) synthetase (PARS) activity in the nuclear fraction was observed in nHS group, associated with an increase in polyADP-ribosylated protein. In contrast, post-hypoxic cell viability of HS group was approximately 60% of the pre-hypoxic value. Hypo/reoxy-induced rise in PARS activity and increase in polyADP-ribosylated protein were attenuated in HS group. To confirm the relationship between an increase in cell viability after Hypo/Reoxy and attenuation of PARS activation, cardiomyocytes without exposure to HS were subjected to Hypo/Reoxy in the presence of 1 mM 3-aminobenzamide, an inhibitor of PARS. Treatment of cells with 3-aminobenzamide attenuated Hypo/ Reoxy-induced decrease in cell viability. These results suggest that Hsp70 translocated into nucleus after HS may attenuate PARS activation during Hypo/Reoxy, leading to the cytoprotection of cardiomyocytes against Hypo/Reoxy injury.

Targeted disruption of NFATc3, but not NFATc4, reveals an intrinsic defect in calcineurin-mediated cardiac hypertrophic growth

A calcineurin-nuclear factor of activated T cells (NFAT) regulatory pathway has been implicated in the control of cardiac hypertrophy, suggesting one mechanism whereby alterations in intracellular calcium handling are linked to the expression of hypertrophy-associated genes. Although recent studies have demonstrated a necessary role for calcineurin as a mediator of cardiac hypertrophy, the potential involvement of NFAT transcription factors as downstream effectors of calcineurin signaling has not been evaluated. Accordingly, mice with targeted disruptions in NFATc3 and NFATc4 genes were characterized. Whereas the loss of NFATc4 did not compromise the ability of the myocardium to undergo hypertrophic growth, NFATc3-null mice demonstrated a significant reduction in calcineurin transgene-induced cardiac hypertrophy at 19 days, 26 days, 6 weeks, 8 weeks, and 10 weeks of age. NFATc3-null mice also demonstrated attenuated pressure overload- and angiotensin II-induced cardiac hypertrophy. These results provide genetic evidence that calcineurin-regulated responses require NFAT effectors in vivo.

Urate homeostasis in polycystic kidney disease: comparison with chronic glomerulonephritic kidney

Autosomal dominant polycystic kidney disease (ADPKD) might affect urate homeostasis and clearance. Renal tubular urate transport was studied by means of probenecid (PB) and pyrazinamide (PZA) tests in individuals with ADPKD and normal renal function as well as various degrees of renal failure (49 patients). Comparisons were made between polycystic and chronic glomerulonephritic kidney (CGNK), as well as with controls (men with normal renal function). Patients with ADPKD and normal renal function showed plasma urate levels within normal range and normal renal urate handling. In contrast higher plasma urate levels comparing to controls were found in patients with CGNK and normal renal function. During the evolution of renal failure ADPKD patients showed lower urate plasma levels and higher renal clearance as well as, fractional urate excretion, comparing to CGNK patients with the same degree of renal failure. In conclusion patients with ADPKD and normal renal function have normal urate handling and plasma urate levels within normal range. With increasing severity of disease and during evolution of renal failure CGNK patients showed higher urate plasma levels and lower clearances comparing to ADPKD patients. When renal disease becomes more advanced there was no difference in renal urate handling between ADPKD and CGNK patients.

Polycystic kidney disease: from the bedside to the gene and back

Collated in this highly personal commentary are the most important research findings of the past 10 years that deal primarily with the renal manifestations of inherited polycystic kidney diseases. Progress in understanding these complex disorders has followed two major concurrent and convergent lines of investigation: genes and genetic mechanisms, and pathogenesis and progression. The field has moved from descriptive pathobiology to the elucidation of molecular mechanisms consequent to genetic and epigenetic events. Doubtless, the favorite works of some who have labored diligently in this field have not been fully exalted, and for this I apologize. Were I the editor, this entire celebratory volume would be used to extol the thrilling growth of knowledge during the tenure of this polycystic kidney disease watcher.

Myocardial Akt Activation and Gender

Abstract —Cardiovascular disease risk is higher in men than women, but the basis for this discrepancy remains controversial. Estrogenic stimulation of the myocardium or isolated cardiomyocytes has been purported to exert multiple beneficial effects associated with inhibition of maladaptive responses to pathogenic insults. This report describes a significant difference between the sexes in myocardial activation of Akt, a protein kinase that regulates a broad range of physiological responses including metabolism, gene transcription, and cell survival. We find that young women possess higher levels of nuclear-localized phospho-Akt 473 relative to comparably aged men or postmenopausal women. Both localization of phospho-Akt 473 in myocardial nuclei of sexually mature female mice versus males and Akt kinase activity in nuclear extracts of hearts from female mice versus males are elevated. Cytosolic localization of phospho-forkhead, a downstream nuclear target of Akt, is also increased in female relative to male mice, suggesting a potential mechanism for cardioprotective nuclear signaling resulting from Akt activation. Phospho-Akt 473 levels and localization at cardiac nuclei are similarly increased in transgenic mice with myocardium-specific expression of insulin-like growth factor I, a proven stimulus for Akt activation. Phospho-Akt 473 is also localized to the nucleus of cultured cardiomyocytes after exposure to 17β-estradiol or genistein (a phytoestrogen in soy protein–based diets), and neonatal exposure of litters to genistein elevated nuclear phospho-Akt 473 localization. The activation of Akt in a gender-dependent manner may help explain differences observed in cardiovascular disease risk between the sexes and supports the potential beneficial effects of estrogenic stimulation.

Inhibition of RNA transcription modulates magnesium-supplemented potassium cardioplegia protection

BACKGROUND

Previously we reported that decreased postischemic functional recovery was associated with increased DNA fragmentation in the aged myocardium. Magnesium-supplemented potassium (K/Mg) cardioplegia ameliorated DNA fragmentation and enhanced post-ischemic functional recovery. We hypothesized that K/Mg cardioprotection might involve either an RNA- or a protein-dependent mechanism.

METHODS

Aged rabbit hearts underwent Langendorff perfusion. Global ischemia hearts (GI) received 30 minutes of global ischemia and 60 minutes of reperfusion; K/Mg hearts received cardioplegia before global ischemia. To investigate the role of RNA and protein synthesis, K/Mg hearts were treated with alpha-amanitin or cycloheximide to inhibit RNA or protein synthesis. We also determined the quantity of DNA fragmentation and RNA/DNA ratio.

RESULTS

Inhibition of RNA but not protein synthesis significantly decreased K/Mg cardioprotection and was associated with significantly decreased postischemic functional recovery (p < 0.05 versus K/Mg), increased DNA fragmentation, and decreased RNA/DNA ratio (p < 0.05 versus K/Mg).

CONCLUSIONS

These results indicate that K/Mg cardioprotection in the aged myocardium was modulated by an RNA-dependent mechanism.

Thyroid hormone regulation of myocardial Na/K-ATPase gene expression

Employing published methods for isolation of cardiac myocyte nuclei from adult rat ventricular myocardium with the use of mechanical disruption without digestive enzymes, we obtained transcriptionally active cardiac myocyte nuclei with sufficient yield and purity. The relative content of Na/K-ATPase subunit mRNAs (alpha 1, alpha 2, and beta 1) in ventricular myocardium of euthyroid rats closely matched the relative rates of transcription of the respective subunit genes determined by nuclear run-on assay. Treatment of hypothyroid rats with T(3)to elicit hyperthyroidism was associated with 2.9-, 7.5-, and seven-fold increases in the contents of alpha 1-, alpha 2, beta 1-mRNAs, respectively. In contrast, rates of transcription of the subunit genes were not changed significantly by T(3), while transcription of the 18 S ribosomal gene was stimulated identical with three-fold by the treatment. A quantitative reverse transcription-polymerase chain reaction assay for measurement of primary RNA transcripts of the beta 1 gene was developed employing a rat genomic DNA fragment that contains the first exon and part of the first intron of the beta 1 gene. The relative abundance of beta 1 primary transcripts did not change in RNA isolated from hypothyroid, euthyroid, and hyperthyroid rats. It is concluded that: (1) The relative contents of Na/K-ATPase subunit mRNAs in euthyroid adult myocardium is primarily controlled at the transcriptional level, and (2) T(3)-induced increases in the contents of Na/K-ATPase subunit mRNAs in the heart is not associated with increased rates of transcription of the subunit genes, and the effect is mediated at the post-transcriptional level.

Inhaled nitric oxide protects against hyperoxia-induced apoptosis in rat lungs

Inhaled nitric oxide (NO), frequently administered in combination with hyperoxic gas mixtures, was recently shown to protect against the injurious consequences of prolonged hyperoxia. We investigated the possibility that this protective effect is attributable to the ability of NO to block pulmonary apoptosis. We show that rats exposed to 100% O2 for 60 h develop severe lung injury consisting of pronounced vascular leak and alveolar apoptosis as inferred from the presence of positive terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling and DNA ladders in agarose gels and a decrease in constitutive procaspase-3 levels. However, the inclusion of NO (20 parts/million) in the hyperoxic gas mixture significantly attenuated both the vascular leak and apoptosis. NO reversed the hyperoxia-associated changes in the activity of the redox-sensitive transcription factors nuclear factor-kappaB, activator protein-1, and Sp1 after 24 h, lowered intercellular adhesion molecule-1 levels, and increased glutathione content. We therefore show, for the first time, that NO can protect against both hyperoxia-induced apoptosis and inflammation. The data suggest that this protection may occur at the transcriptional and caspase-activation levels.

Effects of spatial segmentation in the continuous model of excitation propagation in cardiac muscle

INTRODUCTION

Spatial segmentation is essential for the numerical simulation of excitation propagation in cardiac muscle.

METHODS AND RESULTS

This study evaluated the effects of spatial segmentation on action potential and on the velocity of propagation in a continuous one-dimensional model of cardiac muscle [intracellular and extracellular resistivities along (L) and transverse (T) to the muscle fibers: 402 omega(cm) (R(e), L), 3,620 omega(cm) (R(e), T), 48 omega(cm) (R(e), L), and 126 omega(cm) (R(e), T), J of Physiol 255:335-346, 1976) and either Luo-Rudy (L-R, Circ Res 68:1501-1526, 1991) or Beeler-Reuter (B-R, J Physiol 268:177-210, 1977) ionic currents. Related cable equations for active membrane are derived. Spatial segmentations of < 31.2 microm (L, L-R), < 11.5 microm (T, L-R), < 44.7 microm (L, B-R), and < 16.5 microm (T, B-R) were required for < 1% errors in the characteristic parameters of action potential. Similarly, spatial segmentations of < 54.5 microm (L, L-R), < 20.1 microm (T, L-R), < 84.3 microm (L, B-R), and < 31.2 microm (T, B-R) were required for < 1 % errors in the velocity of conduction.

CONCLUSION

In general, spatial segmentations of < 26.9% and < 50.8% of the space constant of a fully activated membrane gave < 1.0% errors in the characteristic parameters of action potential and in the velocity of propagation, respectively, for both membranes. The action potential duration was relatively insensitive to the spatial segmentation. Our analysis suggests that lambda(full is a better criterion for the selection of spatial segmentation in numerical simulation than the space constant of the resting membrane.

Activation of the skeletal alpha-actin promoter during muscle regeneration

Little is known concerning promoter regulation of genes in regenerating skeletal muscles. In young rats, recovery of muscle mass and protein content is complete within 21 days. During the initial 5-10 days of regeneration, mRNA abundance for IGF-I, myogenin and MyoD have been shown to be dramatically increased. The skeletal alpha-actin promoter contains E box and serum response element (SRE) regulatory regions which are directly or indirectly activated by myogenin (or MyoD) and IGF-I proteins, respectively. We hypothesized that the skeletal alpha-actin promoter activity would increase during muscle regeneration, and that this induction would occur before muscle protein content returned to normal. Total protein content and the percentage content of skeletal alpha-actin protein was diminished at 4 and 8 days and re-accumulation had largely occurred by 16 days post-bupivacaine injection. Skeletal alpha-actin mRNA per whole muscle was decreased at day 8, and thereafter returned to control values. During regeneration at day 8, luciferase activity (a reporter of promoter activity) directed by -424 skeletal alpha-actin and -99 skeletal alpha-actin promoter constructs was increased by 700% and 250% respectively; however, at day 16, skeletal alpha-actin promoter activities were similar to control values. Thus, initial activation of the skeletal alpha-actin promoter is associated with regeneration of skeletal muscle, despite not being sustained during the later stages of regrowth. The proximal SRE of the skeletal alpha-actin promoter was not sufficient to confer a regeneration-induced promoter activation, despite increased serum response factor protein binding to this regulatory element in electrophoretic mobility shift assays. Skeletal alpha-actin promoter induction during regeneration is due to a combination of regulatory elements, at least including the SRE and E box.

Increased levels of myocardial IkappaB-alpha protein promote tolerance to endotoxin

Endotoxin [lipopolysaccharide (LPS)] causes tumor necrosis factor-alpha (TNF-alpha)-mediated myocardial contractile depression. Tolerance to the cardiac toxicity of LPS can be induced by a prior exposure to LPS or by pretreatment with glucocorticoids. The mechanisms by which the myocardium acquires tolerance to LPS remain unknown. LPS causes phosphorylation and degradation of inhibitory kappaB-alpha (IkappaB-alpha), releasing nuclear factor-kappaB (NF-kappaB) to activate TNF-alpha gene transcription. We hypothesized that LPS induces supranormal synthesis of myocardial IkappaB-alpha protein and thus renders the myocardium tolerant to subsequent LPS. Rats were challenged with LPS after pretreatment with LPS, dexamethasone, or saline. In saline-pretreated rats, LPS caused a rapid decrease in myocardial IkappaB-alpha protein levels, activation of NF-kappaB, and increased TNF-alpha production. These events were followed by myocardial contractile depression. After the initial decrease in myocardial IkappaB-alpha, IkappaB-alpha protein levels rebounded to a level greater than control levels by 24 h. Dexamethasone pretreatment similarly increased myocardial IkappaB-alpha protein levels. In rats pretreated with either LPS or dexamethasone, myocardial IkappaB-alpha protein levels remained similar to control levels after LPS challenge. The preserved level of myocardial IkappaB-alpha protein was associated with diminished NF-kappaB activation, attenuated myocardial TNF-alpha production, and improved cardiac contractility. We conclude that LPS and dexamethasone upregulate myocardial IkappaB-alpha protein expression and that an increased level of myocardial IkappaB-alpha protein may promote cardiac tolerance to LPS by inhibition of NF-kappaB intranuclear translocation and myocardial TNF-alpha production.

Thyroid receptor plasticity in striated muscle types: effects of altered thyroid state

This study examined nuclear thyroid receptor (TR) maximum binding capacity (Bmax), dissociation constant (Kd), and TR isoform (alpha1, alpha2, beta1) mRNA expression in rodent cardiac, "fast-twitch white," "fast-twitch red," and "slow-twitch red" muscle types as a function of thyroid state. These analyses were performed in the context of slow-twitch type I myosin heavy-chain (MHC) expression, a 3,5,3'-triiodothyronine (T3)-regulated gene that displays varying responsiveness to T3 in the above tissues. Nuclear T3 binding analyses show that the skeletal muscle types express more TRs per unit DNA than cardiac muscle, whereas the latter has a lower Kd than the former. Altered thyroid state had little effect on either cardiac Bmax or Kd, whereas hypothyroidism increased Bmax in the skeletal muscle types without affecting its Kd. Cardiac muscle demonstrated the greatest mRNA signal of TR-beta1 compared with the other muscle types, whereas the TR-alpha1 mRNA signals were more abundant in the skeletal muscle types, especially fast-twitch red. Hyperthyroidism increased the ratio of beta1 to alpha1 and decreased the ratio of alpha2- to alpha1+beta1-mRNA signal across the muscle types, whereas hypothyroidism caused the opposite effects. The nuclear T3 affinity correlated significantly with the TR-beta1 mRNA expression but not with TR-alpha1 mRNA expression. Collectively, these findings suggest that, despite a divergent pattern of TR mRNA expression in the different muscle types, these patterns follow similar qualitative changes under altered thyroid state. Furthermore, TR expression pattern cannot account for the quantitative and qualitative changes in type I MHC expression that occur in the different muscle types.

The sarco(endo)plasmic reticulum Ca(2+)-ATPase gene is regulated at the transcriptional level during compensated left ventricular hypertrophy in the rat

In mammalian myocardium, relaxation is mainly triggered by the reuptake of calcium from the cytosol to the lumen of the sarcoplasmic reticulum (SR) through the cardiac isoform of the sarco(endo)plasmic reticulum calcium ATPase, SERCA2a. Relaxation abnormalities related to deficient SR Ca(2+)-uptake have been identified in human heart failure and in animal models of cardiac hypertrophy and failure. These alterations have been associated with a reduction in SERCA2a activity and in steady-state SERCA2a protein and mRNA levels. As a first step in the analysis of the mechanisms responsible for this reduction, we have studied a possible down-regulation of the SERCA2 gene transcription during left ventricular hypertrophy (LVH) induced by constriction of the ascending aorta in the rat. Quantifications of the mRNA levels demonstrated no alteration, compared to sham-operated rats, at 5 d after imposition of the pressure overload, whereas a significant decrease was observed at 11 d. Transcription in-vitro experiments (cardiac nuclear run-on assays) performed in isolated cardiomyocytes nuclei showed no changes at 5 d and a 37% reduction of the SERCA2 gene transcription at 11 d. These results strongly suggest that SERCA2 gene expression down-regulation during cardiac hypertrophy occurs, at least in part, at the level of the transcription.

Interactions between adjacent fibers in a cardiac muscle bundle

A strand of cardiac muscle was modeled as a small bundle of individual fibers surrounded by a large volume conductor. The bundle is a uniform assembly of small identical cylindrical fibers, arranged as a series of concentric layers, and its behavior is examined in the presence (coupled bundle) or absence (uncoupled bundle) of transverse resistive coupling between adjacent fibers. Individual fibers are continuous cables of excitable membrane, with circumferential segmentation into 12 equal patches to make the membrane potential changes dependent upon the local interstitial potential. The minimum spacing (d) between adjacent fibers is used to modify the interstitial microstructural organization and the intracellular volume fraction (fi). When d is small enough (d < 0.01 micron), fi remains unchanged at its maximum of about 90%, the interstitial potential is large, the transverse interstitial resistance is high, and the proximity effect arising from the close juxtaposition of adjacent fibers is important. A surface fiber of the uncoupled bundle exhibits little sensitivity to changes in the interstitial microstructure, owing to the dominant influence of the external volume conductor, whereas the central fiber shows a large decrease in velocity, substantial waveshape modifications, and a large increase in interstitial potential as d is reduced. In the coupled bundle, all fibers adopt the same velocity during uniform propagation, owing to the strong transverse resistive coupling; when d is reduced in the range of d < 0.01 micron, the velocity and interstitial potential changes are less pronounced than in the uncoupled bundle. When d is large enough (d > 0.01 micron), the bundle behavior (coupled and uncoupled) approaches that obtained with a bidomain formulation.

Propagation on a central fiber surrounded by inactive fibers in a multifibered bundle model

We studied uniform propagation on a central active fiber surrounded by inactive fibers in a multifibered bundle model lying in a large volume conductor. The behavior of a fully active bundle is considered in a companion paper. The bundle is formed by concentric layers of small cylindrical fibers (radius 5 microns), with a uniform minimum distance (d) between any two adjacent fibers, to yield a bundle radius of about 72 microns. Individual fibers are identical continuous cables of excitable membrane based on a modified Beeler-Reuter model. The intracellular volume fraction (fi) increases to a maximum of about 90% as d is reduced and remains unchanged for d < 0.01 micron. In the range of d < 0.01 micron, the central fiber is effectively shielded from external effects by the first concentric layer of inactive fibers, and a large capacitive load current flows across the surrounding inactive membranes. In addition, the fiber proximity produces a circumferentially nonuniform current density (proximity effect) that is equivalent to an increased average longitudinal interstitial resistance. The conduction velocity is reduced as d becomes smaller in the range of d < 0.1 micron, the interstitial potential becomes larger, and both the maximum rate of rise and time constant of the foot of the upstroke are increased. On the other hand, for d > 0.1 micron, there are negligible changes in the shape of the upstroke, and the behavior of the central fiber is close to that of a uniform cable in a restricted volume conductor. For d larger than about 1.2 microns, the active fiber environment is close to an unbounded isotropic volume conductor.

Functional and structural assessment of intercellular communication. Increased conduction velocity and enhanced connexin expression in dibutyryl cAMP-treated cultured cardiac myocytes

Remodeling of conduction pathways in the hypertrophic response to myocardial injury is a potential mechanism leading to the development of anatomic substrates of lethal arrhythmias. To delineate the responsible mechanisms and to directly relate changes in intercellular coupling at gap junctions with electrophysiological alterations, we studied the effects of cAMP, a mediator of cardiac hypertrophy, on action potential conduction velocity and connexin expression in neonatal rat ventricular myocyte cultures. Conduction velocity was measured with an optical activation mapping technique in cells loaded with the voltage-sensitive dye RH-237. Action potentials were conducted 24% to 29% more rapidly (P < .005) after incubating cultures for 24 hours with the cAMP analogue dibutyryl cAMP (db-cAMP, 1 mmol/L). However, db-cAMP caused no change in the maximum rate of rise of the action potential upstroke, Vmax. Electron and immunofluorescence microscopy revealed a significant increase in the number and size of gap junctions in db-cAMP-treated cells. Immunoblotting showed that the total amounts of the ventricular gap junction proteins connexin43 and connexin45 (Cx43 and Cx45, respectively) increased 2- to 4-fold. Immuno-precipitation of metabolically labeled connexin proteins revealed a dose-dependent increase in the rate of Cx45 protein synthesis in myocytes exposed to db-cAMP ( > 2-fold after a 4-hour exposure) but no change in the Cx43 synthesis rate. Northern blot analysis demonstrated a time-dependent increase in the amount of Cx43 mRNA, with a maximum 3.3-fold increase after 4 hours of exposure to 1 mmol/L db-cAMP; cycloheximide did not block this effect. In contrast, Cx45 mRNA levels were not altered significantly after db-cAMP treatment. Thus, cAMP causes a significant increase in conduction velocity that appears to be attributable largely to enhanced expression of proteins responsible for intercellular communication. Cx43 and Cx45 levels appear to be upregulated by cAMP by disparate molecular mechanisms.

Long-term follow up of patients with classical phenylketonuria after diet relaxation at 5 years of age. The Paris Study

The age for discontinuing dietary treatment of phenylketonuria (PKU) has been a worldwide source of controversy for many years. It is the reason we report here the results of a prospective, controlled study in which the diet was relaxed at 5 years of age in 31 so far well-treated children with classical PKU. The increase of phenylalanine (Phe) plasma levels to about 1500 mumol/l (25 mg/dl) after relaxing the diet was not associated with any significant decline of intellectual performance as measured by the Wechsler scores. Paired comparisons at 7-8 years and 11-13 years of age (n = 12) have shown WISC scores of 102.6 +/- 16.2 and 104.8 +/- 16, respectively, which were not significantly different. Similarly, paired comparisons at 9-10 years and 14-16 years (n = 6) did not demonstrate a significant loss of IQ points (107.7 +/- 13 vs 104.8 +/- 18). Of course, it is possible to argue that we should have observed an increase in IQ with increasing age in our patients and that the absence of deterioration cannot be considered by itself as a good result. Nevertheless, it cannot be excluded that the subtle but global intellectual impairments that have been documented in early-treated subjects are, to a very substantial degree, determined in the pre-school years, long before there is any question of stopping or relaxing the diet.

Multiphasic action of glucose and alpha-ketoisocaproic acid on the cytosolic pH of pancreatic beta-cells. Evidence for an acidification pathway linked to the stimulation of Ca2+ influx

Glucose stimulation raises the pHi of pancreatic beta-cells, but the underlying mechanisms are not well understood. We have now investigated the acute effects of metabolizable (glucose and the mitochondrial substrate alpha-ketoisocaproic acid, KIC) and nonmetabolizable (high K+ and the K-ATP channel blocker tolbutamide) insulin secretagogues on the pHi of pancreatic beta-cells isolated from normal mice, as assessed by BCECF fluorescence from single cells or islets in the presence of external bicarbonate. The typical acute effect of glucose (22-30 mM) on the pHi was a fast alkalinization of approximately 0.11 unit, followed by a slower acidification. The relative expression of the alkalinizing and acidifying components was variable, with some cells and islets displaying a predominant alkalinization, others a predominant acidification, and others yet a mixed combination of the two. The initial alkalinization preceded the [Ca2+]i rise associated with the activation of voltage-sensitive Ca2+ channels. There was a significant overlap between the glucose-evoked [Ca2+]i rise and the development of the secondary acidification. Depolarization with 30 mM K+ and tolbutamide evoked pronounced [Ca2+]i rises and concomitant cytosolic acidifications. Blocking glucose-induced Ca2+ influx (with 0 Ca2+, nifedipine, or the K-ATP channel agonist diazoxide) suppressed the secondary acidification while having variable effects (potentiation or slight attenuation) on the initial alkalinization. KIC exerted glucose-like effects on the pHi and [Ca2+]i, but the amplitude of the initial alkalinization was about twice as large for KIC relative to glucose. It is concluded that the acute effect of glucose on the pHi of pancreatic beta-cells is biphasic. While the initial cytosolic alkalinization is an immediate consequence of the activation of H+-consuming metabolic steps in the mitochondria, the secondary acidification appears to originate from enhanced Ca2+ turnover in the cytoplasm. The degree of coupling between glucose metabolism and Ca2+ influx as well as the relative efficacies of these processes determines whether the acute pHi response of a beta-cell (or of a tightly coupled multicellular system such as an islet of Langerhans) is predominantly an alkalinization, an acidification, or a mixed proportion of the two.

Criteria for evaluating abnormal signal-averaged electrocardiogram in children classified by age, body surface area and height

We evaluated criteria for the diagnosis of ventricular abnormal signal-averaged electrocardiogram (SAE) in 205 healthy children classified by age, body surface area and height. The children were classified by age into 4 groups: under 3 months old, 3 months old or more but less than 1 year old, 1 year old or more but less than 12 year old and 12 year old or more. They were also divided by body surface area into 4 groups: under 0.3 m2, 0.3 m2 or more but less than 0.5 m2, 0.5 m2 or more but less than 1.2 m2, and 1.2 m2 or more. In terms of height, they were classified into 4 groups: under 60 cm, 60 cm or more but less than 80 cm, 80 cm or more but less than 140 cm, and 140 cm or more. The boundary points in these 3 classifications were statistically consistent. Criteria for abnormal SAE in children classified according to age were filtered QRS duration (f-QRSd) > 95 msec, root mean square (RMS) < 30 mu v and duration of low amplitude signal (LAS) > 25 msec in those under 3 months old; f-QRSd > 110 msec, RMS < 25 mu v, LAS > 30 msec in those 3 months or more but less than 1 year old; f-QRSd > 115 msec, RMS < 20 mu v, LAS > 30 msec in those 1 year old or more but less than 12 year old; and f-QRSd > 125 msec, RMS < 20 mu v, LAS > 30 msec in those 12 year old or more. The criteria for evaluating abnormal SAE were similar regardless of whether children were classified by age, body surface area or height. Using these values as criteria, the 205 children were evaluated for the presence of abnormal SAE. All of the children were negative for abnormal SAE using these criteria according to age, body surface area or height. In evaluating abnormal SAE in children, it is useful to classify children by age, body surface area and height and to identify the criteria in each group. In this study, the criteria based on height and age were particularly useful, since these are more convenient than body surface area.

A possible role of the ATP-sensitive potassium ion channel in determining the duration of spike-bursts in mouse pancreatic beta-cells

The pancreatic beta-cell displays an electrical activity consisting of spike bursts and silent phases at glucose concentrations of about 10 mM. The mechanism of initial depolarization induced by glucose is well defined. However, the mechanism inducing the silent phase has not been fully elucidated. In the present study, the possibility of involvement of ATP-sensitive K+ channels in repolarization was examined using the patch-clamp technique in the cell-attached recording configuration. Ouabain (0.1 mM), an inhibitor of Na+/K+-ATPase, caused a complete suppression of ATP-sensitive K+ channel activity followed by typical biphasic current deflections, which were due to action potentials. The channel activity was also inhibited by removal of K+ from a perifusion solution. Furthermore, the activity of ATP-sensitive K+ channels was markedly inhibited either by replacement of external NaCl with LiCl or by addition of amiloride (0.2 mM), a blocker of Na+/H+ antiport. Addition of L-type Ca2+ channel blockers such as Nifedipine for Mn2+ induced the complete suppression of K+ channel activity. These findings strongly suggest that a fall in ATP consumption results in sustained depolarization, and that the repolarizations interposed between spike-bursts under normal ionic conditions are due to the periodical fall of ATP concentration brought about by periodical acceleration of ATP consumption at Na+/K+-pumps. It is concluded that the elevation of intracellular Na+ concentration as a consequence of accelerated Na+/Ca2+-countertransport during the period of spike-burst enhances ATP consumption, leading to a fall in ATP concentration which is responsible for termination of spike-burst and initiation of repolarization.

Isolation of pepsin-resistant laminin fragments from human placenta: effect on epithelial cells cultured from the kidneys of patients with autosomal dominant polycystic kidney disease (ADPKD)

Laminin isolated from human placenta was subjected to prolonged pepsin digestion. Seven peptide fragments (designated N1 to N7) were separated by ion-exchange chromatography and gel filtration and characterised by SDS-polyacrylamide gel electrophoresis and immunoblotting. The molecular size of the laminin fragments varied from approx. 900,000 (N1) to 28,000 (N7). Epithelial cells obtained from normal kidneys and patients with autosomal dominant polycystic kidney disease (ADPKD) were cultured. The incorporation of [3H]thymidine was measured over 96 h to determine the effect of the addition of the different fragments and whole laminin from EHS tumour to the cells. The rate of growth of both normal and polycystic cells was increased in the presence of the laminin fragments but this effect was more pronounced in the ADPKD cells.

Determinants and mechanisms of flecainide-induced promotion of ventricular tachycardia in anesthetized dogs

BACKGROUND

Class IC antiarrhythmic agents such as flecainide are known to have potentially significant ventricular proarrhythmic actions, but the underlying mechanisms are incompletely understood. While some studies have reported proarrhythmia in both healthy dogs and dogs that previously have had a myocardial infarction (MI), there are no published, controlled studies comparing proarrhythmia in healthy dogs vs in dogs with MI. In addition, the concentration dependence of proarrhythmia is unknown and the electrophysiological changes associated with proarrhythmia are not well established.

METHODS

We administered successive loading and maintenance infusions of flecainide until ventricular tachyarrhythmia or death occurred in 13 healthy dogs and 19 dogs with 72-hour-old MIs (MI dogs). Ventricular proarrhythmia, defined as reproducible ventricular tachycardia absent under control conditions and occurring in the presence of flecainide, was observed in 4 of 13 healthy dogs (31%) and 15 of 19 MI dogs (79%, P = .02), and drug-induced spontaneous ventricular tachycardia occurred in 8 of 19 MI dogs but in no healthy dogs (P = .007). Activation data at the time of proarrhythmia were available for 11 MI dogs and provided evidence for reentry in 9, with a complete epicardial reentry circuit identified in 4 dogs and a partial circuit in 5. While flecainide slowed ventricular conduction in both the longitudinal and transverse directions, there were no significant differences between overall drug-induced conduction changes in MI dogs compared with healthy dogs. However, in 7 MI dogs for whom activation data were available during ventricular pacing at concentrations comparable to those causing proarrhythmia, flecainide induced a new arc of block in 6 of 7, whereas an arc of block was never observed in the absence of proarrhythmia. Conduction block was induced transverse to fiber orientation in a rate-dependent fashion and was caused by a regionally-specific effect of the drug. No differences were noted between refractory periods proximal and distal to the site of block.

CONCLUSIONS

Prior MI strongly predisposes dogs to flecainide proarrhythmia, which occurs in the majority of such dogs in a concentration-related way. In most cases, activation data suggest that anisotropic reentry around a localized arc of rate-dependent transverse conduction block underlies proarrhythmia. These results provide insights into the conditions and mechanisms underlying the ability of flecainide to promote the occurrence of ventricular tachycardia.

Myocardial mitochondrial calcium accumulation modulates nuclear calcium accumulation and DNA fragmentation

BACKGROUND

Previously, we have shown that normothermic global ischemia increases cytosolic calcium accumulation in both the mature and aged heart. Increased nuclear and mitochondrial calcium accumulation was shown to occur in the aged but not the mature heart, and these age-related differences were associated with increased DNA fragmentation and decreased cellular viability only in the aged heart.

METHODS

To investigate the relationship between increased mitochondrial and nuclear calcium and DNA fragmentation, mature and aged rabbit hearts were subjected to normothermic global ischemia with and without the addition of ruthenium red to block mitochondrial calcium influx. Cytosolic calcium accumulation was measured in a parallel experiment using fura-2.

RESULTS

Ruthenium red ameliorated mitochondrial calcium accumulation and was associated with both decreased DNA fragmentation and decreased nuclear calcium accumulation.

CONCLUSIONS

Nuclear calcium accumulation was correlated with increased mitochondrial calcium accumulation but not increased cytosolic calcium accumulation in the aged heart. Modulation of mitochondrion "futile calcium cycling" may be of significance in the modulation of ischemic myocardial injury.

The role of metabolism, cytoplasmic Ca2+, and pH-regulating exchangers in glucose-induced rise of cytoplasmic pH in normal mouse pancreatic islets

Intact mouse islets were loaded with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein to study the effects of glucose on cytoplasmic pH (pHi) in pancreatic B-cells. In HCO3- buffer, glucose produced a steady-state increase in pHi that required metabolism of the sugar and was concentration-dependent between 0 and 10 mM (Km approximately 5 mM) before plateauing at a maximum value of approximately 0.2 pH units. In HEPES buffer, glucose concentrations above 7 mM caused an initial rise followed by a secondary decrease and an eventual return to about initial values. Inhibition of Ca2+ influx had little effect on the pHi changes produced by glucose in HCO3- medium, but unmasked an alkalinizing effect in HEPES buffer. Raising cytoplasmic Ca2+ by 30 mM potassium caused a larger acidification in HEPES than in HCO3- buffer, but a subsequent rise in glucose now increased pHi in both types of buffer. In the presence of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; inhibitor of HCO3-/Cl- exchange), the effect of glucose on pHi in HCO3- buffer became similar to that in HEPES buffer. After inhibition of the Na+/H+ exchanger by dimethylamiloride, glucose produced a marked and sustained fall in pHi in HEPES buffer. A similar fall was seen in HCO3- buffer only when DIDS and dimethylamiloride were present together. However, if Ca2+ influx was prevented when both exchangers were blocked, glucose increased pHi. In conclusion, the metabolism of glucose tends to increase pHi in B-cells, whereas the concomitant rise in [Ca2+]i exerts an acidifying action. In HEPES buffer, this acidifying effect of Ca2+ is offset by the operation of the Na+/H+ exchanger. In physiological HCO3- buffer, the activity of the HCO3-/Cl- exchanger overcompensates and leads to an increase in pHi.

Magnesium cardioplegia reduces cytosolic and nuclear calcium and DNA fragmentation in the senescent myocardium

Previous reports have indicated that the senescent myocardium is less tolerant to surgically induced ischemia and that diminished functional recovery is associated with alterations in cytosolic calcium ([Ca2+]i) accumulation. Recently, increased [Ca2+]i has been suggested to alter nuclear calcium ([Ca2+]n) accumulation. To investigate the relation between [Ca2+]i and [Ca2+]n, we subjected mature and aged rabbit hearts to normothermic global ischemia, either without treatment or after treatment with potassium cardioplegia, magnesium cardioplegia, or a combination of potassium and magnesium cardioplegia. The relation between altered [Ca2+]n and DNA fragmentation was also investigated. Our results indicate that [Ca2+]i was increased during 30 minutes of normothermic global ischemia without treatment in both the mature and aged hearts (p < 0.05). Accumulation of [Ca2+]i during global ischemia was reduced with the use of potassium, magnesium, and a combination of potassium and magnesium cardioplegia (p < 0.05 versus untreated ischemia) in both the mature and aged hearts. Levels of [Ca2+]n were unaffected by global ischemia or cardioplegia in the mature myocardium; however, in the aged myocardium, [Ca2+]n was increased during global ischemia and with potassium cardioplegia and was associated with increased nuclear DNA fragmentation (p < 0.05). The use of magnesium and a combination of potassium and magnesium cardioplegia attenuated [Ca2+]n accumulation and nuclear DNA fragmentation (p < 0.05). Control of [Ca2+]i and [Ca2+]n was associated with enhanced functional recovery during reperfusion. These results indicate that during normothermic ischemia, there is increased [Ca2+]i and [Ca2+]n in the aged myocardium, and increased [Ca2+]n is associated with increased nuclear DNA fragmentation.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular pH, cytosolic calcium concentration and electrical activity in RINm5F insulinoma cells

The addition of L-lactate or acetate to RINm5F cells caused a transient intracellular acidification, an increase in [Ca2+]i and induced electrical activity. The subsequent withdrawal of lactate or acetate resulted in an intracellular alkalinization with no apparent changes in [Ca2+]i nor electrical activity. Intracellular alkalinization and acidification by application by application and withdrawal of NH4Cl were both accompanied by transient increases in [Ca2+]i in the absence of electrical activity. The induction of electrical activity by lactate was associated with the appearance of inward whole cell currents. Changes in intracellular pH may affect [Ca2+]i though not necessarily by altering plasma membrane potential. The inward currents associated with lactate application may represent an organic anion conductance contributing towards the stimulation of electrical activity by organic acids.

Age-related criteria for signal-averaged electrocardiographic late potentials in children

This study examined the age-related criteria of signal-averaged electrocardiographic (SA-ECG) parameters in children. SA-ECGs were obtained in 82 healthy volunteers in six groups depending on age (group 1: 1 day to < 1 month; group 2: 1 month to < 1 year; group 3: 1 to < 6 years; group 4: 6 to < 12 years; group 5: 12 to < 20 years; group 6: 20 to < 40 years). To examine the effect of heart rate on the parameters of SA-ECG, right atrial pacings were performed in 4 children with a ventricular septal defect aged 1-7 years. The root mean square voltage (RMS) was high; and the filtered QRS (f-QRS) duration and the duration of the low amplitude signal (LAS) were low during childhood, especially in infants (group 2), compared with those in adults. Late duration (LD) had no significant difference among age groups. The criteria for ventricular late potential were as follows: RMS < 25 microV, LAS > 35 ms, f-QRS duration > 110 ms, and LD > 35 ms for those age 1 day to < 1 month; RMS < 40 microV, LAS > 30 ms, f-QRS duration > 100 ms, and LD > 35 ms for those age 1 month to < 1 year; RMS < 20 microV, LAS > 40 ms, f-QRS duration > 130 ms, and LD > 35 ms for those age 1 to < 20 years; and RMS < 15 microV, LAS > 45 ms, f-QRS duration > 135 ms, and LD > 35 ms for those age 20 to < 40 years. RMS and LAS correlated with f-QRS duration (r = -0.78 and 0.76, respectively; p < 0.05), suggesting that these parameters are associated with the thickness of the ventricular muscle and the ventricular conduction time. Right atrial pacing had no effect on the measured SA-ECG parameters. The age-related differences in SA-ECG parameters might be due to age-related differences in the thickness of the ventricular muscle and the ventricular conduction time but are not due to differences in the heart rate. The age difference of each parameter on SA-ECG should be considered for ventricular late potentials.