Search PubMed⌕ Search

Biomedical subjects

A Terzic

Publications and source records attributed to A Terzic.

At least 55 records · Page 3Linked to original sources
PubMed1999

Adenylate kinase-catalyzed phosphotransfer in the myocardium : increased contribution in heart failure.

Although the downregulation of creatine kinase activity has been associated with heart failure, creatine kinase-deficient transgenic hearts have a preserved contractile function. This suggests the existence of alternative phosphotransfer pathways in the myocardium, the identity of which is still unknown. In this study, we examined the contribution of adenylate kinase-catalyzed phosphotransfer to myocardial energetics. In the isolated mitochondria/actomyosin system, which possesses endogenous adenylate kinase activity in both compartments, substrates for adenylate kinase promoted the rate and amplitude of actomyosin contraction that was further enhanced by purified adenylate kinase. Inhibition of adenylate kinase activity diminished both actomyosin contraction and mitochondrial respiration, which indicated reduced energy flow between mitochondria and myofibrils. In intact myocardium, the net adenylate kinase-catalyzed phosphotransfer rate was 10% of the total ATP turnover rate as measured by 18O-phosphoryl labeling in conjunction with gas chromatography and mass spectrometry. In pacing-induced failing heart, adenylate kinase-catalyzed phosphotransfer increased by 134% and contributed 21% to the total ATP turnover. Concomitantly, the contribution by creatine kinase dropped from 89% in normal hearts to 40% in failing hearts. These phosphotransfer changes were associated with reduced levels of metabolically active ATP but maintained overall ATP turnover rate. Thus, this study provides evidence that adenylate kinase facilitates the transfer of high-energy phosphoryls and signal communication between mitochondria and actomyosin in cardiac muscle, with an increased contribution to cellular phosphotransfer in heart failure. This phosphotransfer function renders adenylate kinase an important component for optimal myocardial bioenergetics and a compensatory mechanism in response to impaired intracellular energy flux in the failing heart.

Actomyosin↗
PubMed1999

Regulation of nitric oxide-responsive recombinant soluble guanylyl cyclase by calcium.

Calcium (Ca2+) and cyclic GMP (cGMP) subserve antagonistic functions that are reflected in their coordinated reciprocal regulation in physiological systems. However, molecular mechanisms by which Ca2+ regulates cGMP-dependent signaling remain incompletely defined. In this study, the inhibition of recombinant nitric oxide (NO)-stimulated soluble guanylyl cyclase (SGC) by Ca2+ was demonstrated. The alpha- and beta-subunits of recombinant rat SGC were heterologously coexpressed in HEK 293 cells which do not express NO synthase, whose Ca2+-stimulated activity can confound the effects of that cation on SGC. Ca2+ inhibited basal and NO-stimulated SGC in a concentration- and guanine nucleotide-dependent fashion. This cation inhibited SGC in crude cell extracts and immunopurified preparations. Ca2+ lowered both the Vmax and Km of SGC via an uncompetitive mechanism through direct interaction with the enzyme. In intact HEK 293 cells, increases in the intracellular Ca2+ concentration induced by ionomycin, a Ca2+ ionophore, and thapsigargin, which releases intracellular stores of that cation, inhibited NO-stimulated intracellular cGMP accumulation. Similarly, carbachol-induced elevation of the intracellular Ca2+ concentration inhibited NO-stimulated intracellular cGMP accumulation in HEK 293 cells. These data demonstrate that SGC behaves as a sensitive Ca2+ detector that may play a central role in coordinating the reciprocal regulation of Ca2+- and cGMP-dependent signaling mechanisms.

Animals↗
PubMed1999

Physical association between recombinant cardiac ATP-sensitive K+ channel subunits Kir6.2 and SUR2A.

The inwardly-rectifying K+ channel Kir6.2 serves as a common pore-forming core in various ATP-sensitive K+ (KATP) channels, and it is through assembly with sulfonylurea-receptor (SUR) isoforms, which are ATP-binding cassette (ABC) proteins, that tissue-specific channel phenotypes can be generated. In this regard, Kir6.2 has been shown to physically associate with SUR1 to form the pancreatic KATP channel. While cardiac KATP channel activity can be reconstituted by coexpression of Kir6.2 with a distinct SUR isoform, SUR2A, no direct proof has been provided for physical association between these two proteins. Therefore, we tested, by a coimmunoprecipitation procedure in conjunction with an amino-terminal Kir6.2-antibody, physical association between recombinant Kir6.2 and SUR2A. From a mixture of Kir6.2 and SUR2A in vitro-translated proteins, the Kir6.2-specific antibody coimmunoprecipitated 38-kDa and 140-kDa proteins corresponding to Kir6.2 and SUR2A, respectively. In the absence of Kir6.2, SUR2A was not precipitated by the anti-Kir6.2 antibody, indicating that the antibody recognized SUR2A only when SUR2A formed a complex with Kir6.2. A Kir6.2 deletion mutant lacking 37 amino acids from the carboxyterminus still coimmunoprecipitated with SUR2A, indicating that the distal carboxy-terminus of Kir6.2 is unnecessary for subunit association. Kir6.2 mutants lacking more proximal carboxy-terminus regions, including the M2 transmembrane domain, failed to immunoprecipitate SUR2A, suggesting that the proximal carboxyterminus together with the M2 domain are required for channel assembly. These deletion constructs supported cellular distribution of Kir6.2. Thus, the present study provides direct evidence for physical association between Kir6.2 and SUR2A, essentially reconstituting the cardiac KATP channel in vitro. The demonstration of complex formation between Kir6.2 and SUR2A indicates that the structural basis for channel function may rely on direct physical interaction of the two subunits.

Adenosine Triphosphate↗
PubMed1999

Sulfonylurea drugs increase early mortality in patients with diabetes mellitus after direct angioplasty for acute myocardial infarction.

OBJECTIVES: The purpose of this study was to examine the impact of sulfonylurea drug use on outcome in diabetic patients undergoing direct coronary angioplasty for acute myocardial infarction. BACKGROUND: Sulfonylurea drugs impair ischemic preconditioning. Whether sulfonylurea drugs affect outcome adversely in diabetic patients undergoing direct angioplasty for acute myocardial infarction is unknown. METHODS: Clinical outcomes after direct balloon angioplasty for acute myocardial infarction were evaluated in 67 diabetic patients taking oral sulfonylurea drugs and 118 diabetic patients not taking these drugs. RESULTS: Hospital mortality was significantly higher among diabetics treated with sulfonylurea drugs at the time of myocardial infarction (24% vs. 11%). Univariate analysis identified sulfonylurea drug, age, ventricular function, ejection fraction less than 40%, prior bypass surgery and congestive heart failure as correlates of increased in-hospital mortality. Logistic regression found sulfonylurea drug use (odds ratio 2.77, p=0.017) to be independently associated with early mortality. Congestive heart failure, but not sulfonylurea drug use, was associated with an increased incidence of in-hospital ventricular arrhythmias. Congestive heart failure, prior bypass surgery and female gender, but not sulfonylurea drug use, were associated with late adverse events. CONCLUSIONS: Sulfonylurea drug use is associated with an increased risk of in-hospital mortality among diabetic patients undergoing coronary angioplasty for acute myocardial infarction. This early risk is not explained by an increase in ventricular arrhythmias, but may reflect deleterious effects of sulfonylurea drugs on myocardial tolerance for ischemia and reperfusion. For surviving patients sulfonylurea drug use is not associated with an increased risk of serious late adverse events.

Adult↗
PubMed1999

Reduced activity of enzymes coupling ATP-generating with ATP-consuming processes in the failing myocardium.

Coupling of ATP-generating with ATP-consuming processes is an essential component in the cardiac bioenergetics responsible for optimal myocardial function. Although a number of enzymatic systems have been implicated in securing proper intracellular energy communication, their integrative response in a failing myocardium has not been determined so far. Therefore, we measured catalytic activities of enzymes responsible for the communication between ATP-generating and ATP-consuming processes in ventricular samples obtained from normal dogs and dogs with tachycardia-induced heart failure. In the failing myocardium, phosphotransfer activities of creatine kinase, adenylate kinase, 3-phosphoglycerate kinase and pyruvate kinase, which collectively deliver ATP and remove ADP from myofibrillar ATPases, were depressed by 30, 21, 44 and 20%, respectively, when compared to normal controls. The activity of hexokinase, an enzyme which directs phosphoryls into the glycolytic phosphotransfer pathway, was unchanged. Also, the activity of glyceraldehyde-3-phosphate dehydrogenase, which may shuttle inorganic phosphate between ATPases and ATP-synthases, was not affected by heart failure. However, the CO2-hydration activity of carbonic anhydrase, which together with creatine kinase, is presumed responsible for removal of protons from ATPases, was diminished by 21%. As these enzymatic systems are collectively required for adequate delivery of high-energy phosphoryl to, and removal of end-products from, cellular ATPases, the cumulative deficit in their flux capacities may provide a bioenergetic basis for impaired contraction-relaxation in the failing heart.

Adenosine Diphosphate↗
PubMed1999

Inhibition of both Na/H and bicarbonate-dependent exchange is required to prevent recovery of intracellular pH in single cardiomyocytes exposed to metabolic stress.

Although tight regulation of intracellular pH (pHi) is critical for the survival under stress, paradoxically a slowed recovery of pHi under hypoxic injury may be cardioprotective. In this study, we investigated the recovery of pHi after hypoxia-induced intracellular acidosis in cardiomyocytes loaded with the H+-sensitive dye SNARF-1. Exposure of single cardiomyocytes to 2,4-dinitrophenol (DNP), an inhibitor of mitochondrial oxidative phosphorylation, induced significant intracellular acidification. However, within 10-12 min upon removal of DNP, cardiomyocytes restituted their intracellular H+ concentration. The presence either of 5-N-ethyl-N-isopropylamiloride (EIPA) an inhibitor of Na/H antiporter, or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of bicarbonate-dependent exchange, did not modify the cellular response to DNP. But, combined use of EIPA and DIDS prevented the restitution of intracellular pH following removal of DNP. This study, thus, demonstrated, for the first time, that blockade of both Na/H and bicarbonate-dependent exchange is necessary and sufficient to maintain the hypoxia-induced intracellular acidification. Therefore, concomitant blockade of both pH-regulating mechanisms deserves to be further considered as a novel strategy against hypoxia-reoxygenation injury in the heart.

2,4-Dinitrophenol↗
PubMed1999

Channelopathies of inwardly rectifying potassium channels.

Mutations in genes encoding ion channels have increasingly been identified to cause disease conditions collectively termed channelopathies. Recognizing the molecular basis of an ion channel disease has provided new opportunities for screening, early diagnosis, and therapy of such conditions. This synopsis provides an overview of progress in the identification of molecular defects in inwardly rectifying potassium (Kir) channels. Structurally and functionally distinct from other channel families, Kir channels are ubiquitously expressed and serve functions as diverse as regulation of resting membrane potential, maintenance of K(+) homeostasis, control of heart rate, and hormone secretion. In humans, persistent hyperinsulinemic hypoglycemia of infancy, a disorder affecting the function of pancreatic beta cells, and Bartter's syndrome, characterized by hypokalemic alkalosis, hypercalciuria, increased serum aldosterone, and plasma renin activity, are the two major diseases linked so far to mutations in a Kir channel or associated protein. In addition, the weaver phenotype, a neurological disorder in mice, has also been associated with mutations in a Kir channel subtype. Further genetic linkage analysis and full understanding of the consequence that a defect in a Kir channel would have on disease pathogenesis are among the priorities in this emerging field of molecular medicine.

Animals↗
PubMed1999

Interruption of transmembrane signaling as a novel antisecretory strategy to treat enterotoxigenic diarrhea.

Bacteria that produce heat-stable enterotoxins (STs), a leading cause of secretory diarrhea, are a major cause of morbidity and mortality worldwide. ST stimulates guanylyl cyclase C (GCC) and accumulation of intracellular cyclic GMP ([cGMP]i), which opens the cystic fibrosis transmembrane conductance regulator (CFTR)-related chloride channel, triggering intestinal secretion. Although the signaling cascade mediating ST-induced diarrhea is well characterized, antisecretory therapy targeting this pathway has not been developed. 2-ChloroATP (2ClATP) and its cell-permeant precursor, 2-chloroadenosine (2ClAdo), disrupt ST-dependent signaling in intestinal cells. However, whether the ability to disrupt guanylyl cyclase signaling translates into effective antisecretory therapy remains untested. In this study, the efficacy of 2ClAdo to prevent ST-induced water secretion by human intestinal cells was examined. In Caco-2 human intestinal cells, ST increased [cGMP]i, induced a chloride current, and stimulated net basolateral-to-apical water secretion. This effect on chloride current and water secretion was mimicked by the cell-permeant analog of cGMP, 8-bromo-cGMP. Treatment of Caco-2 cells with 2ClAdo prevented ST-induced increases in [cGMP]i, chloride current and water secretion. Inhibition of the downstream consequences of ST-GCC interaction reflects proximal disruption of cGMP production because 8-bromo-cGMP stimulated chloride current and water secretion in 2ClAdo-treated cells. Thus, this study demonstrates that disruption of guanylyl cyclase signaling is an effective strategy for antisecretory therapy and provides the basis for developing mechanism-based treatments for enterotoxigenic diarrhea.

2-Chloroadenosine↗
PubMed1999

Gene delivery of Kir6.2/SUR2A in conjunction with pinacidil handles intracellular Ca2+ homeostasis under metabolic stress.

Metabolic injury is a complex process affecting various tissues, with intracellular Ca2+ loading recognized as a common precipitating event leading to cell death. We have recently observed that cells overexpressing recombinant ATP-sensitive K+ (KATP) channel subunits may acquire resistance against metabolic stress. To examine whether, under metabolic challenge, intracellular Ca2+ homeostasis can be maintained by an activator of channel proteins, we delivered Kir6.2 and SUR2A genes, which encode KATP channel subunits, into a somatic cell line lacking native KATP channels. Hypoxia-reoxygenation was simulated by application and removal of the mitochondrial poison 2,4 dinitrophenol. Under such metabolic stress, Ca2+ loading was induced by Ca2+ influx during hypoxia and release of Ca2+ from intracellular stores during reoxygenation. Delivery of Kir6.2/SUR2A genes, in conjunction with the KATP channel activator pinacidil, prevented intracellular Ca2+ loading irrespective of whether the channel opener was applied throughout the duration of hypoxia-reoxygenation or transiently during the hypoxic or reoxygenation stage. In all stages of injury, the effect of pinacidil was inhibited by the selective antagonist of KATP channel, 5-hydroxydecanoate. The present study provides evidence that combined use of gene delivery and pharmacological targeting of recombinant proteins can handle intracellular Ca2+ homeostasis under hypoxia-reoxygenation irrespective of the stage of the metabolic insult.

Animals↗
PubMed1999

Noninsulinoma pancreatogenous hypoglycemia: a novel syndrome of hyperinsulinemic hypoglycemia in adults independent of mutations in Kir6.2 and SUR1 genes.

In adults, endogenous hyperinsulinemic hypoglycemia is almost invariably due to insulinoma. In these patients with insulinoma, neuroglycopenic episodes exclusively after meal ingestion and negative 72-h fasts are extraordinarily rare. We describe five adults with neuroglycopenic episodes from hyperinsulinemic hypoglycemia within 4 h of meal ingestion and negative 72-h fasts. Each had negative transabdominal ultrasonography, spiral computed tomographic scanning, and celiac axis angiography of the pancreas. However, all showed positive selective arterial calcium stimulation tests indicative of pancreatic beta-cell hyperfunction. At pancreatic exploration, no insulinoma was detected by intraoperative ultrasonography and complete mobilization and palpation of the pancreas. Moreover, the resected pancreata showed islet hypertrophy and nesidioblastosis, but no insulinoma. No definite disease-causing mutation was detected in Kir6.2 and SUR1 genes, which encode the subunits of the pancreatic ATP-sensitive potassium channel responsible for glucose-induced insulin secretion. Four patients who underwent gradient-guided partial pancreatectomy have been free of hypoglycemic symptoms for up to 3 yr follow-up; the other, who underwent a limited distal pancreatectomy, has had brief recurrence of symptoms. The unique clinical features and responses to dynamic testing in these adults with hyperinsulinemic hypoglycemia in the absence of insulinoma may constitute a new syndrome of postprandial hypoglycemia from diffuse beta-cell hyperfunction.

Adolescent↗
PubMed1999

Increased number of cardiomyocytes in cross-sections from tachycardia-induced cardiomyopathic hearts.

Based on positive identification of DNA replication and mitotic division in cardiomyocytes isolated from failing hearts, it has been proposed that adult ventricular cardiomyocytes can gain the capacity to proliferate with progression of heart failure. However, due to the lack of a reliable method to distinctly image individual cardiac cells within the myocardial syntitium, such a concept still remains largely controversial. In the present study, we used laser confocal microscopy, to image cross-sections of intact myocardium stained with fluorescein-conjugated wheat germ agglutinin and propidium iodide. This approach allowed to clearly separate the profile of individual myocytes within cardiac tissue sections. We found that in the left ventricles of dogs, subjected to tachycardia-induced cardiomyopathy, the number of cells was significantly increased in both longitudinal and transversal sections. Treatment with the angiotensin-converting enzyme inhibitor, enalapril, reversed these changes to values similar to those found in controls. Therefore, this study provides evidence, at the in situ level, for cellular hyperplasia in heart failure. This supports the more general notion that adult cardiomyocytes may not be terminally differentiated, and that an increase in cell number could contribute to the increase in left ventricular mass observed with progression of disease.

Animals↗
PubMed1998

Recombinant cardiac ATP-sensitive K+ channel subunits confer resistance to chemical hypoxia-reoxygenation injury.

BACKGROUND: Opening of cardiac ATP-sensitive K+ (KATP) channels has emerged as a promising but still controversial cardioprotective mechanism. Defining KATP channel function at the level of recombinant channel proteins is a necessary step toward further evaluation of the cardioprotective significance of this ion conductance. METHODS AND RESULTS: KATP channel deficient COS-7 cells were found to be vulnerable to chemical hypoxia-reoxygenation injury that induced significant cytosolic Ca2+ loading (from 97+/-3 to 236+/-11 nmol/L). In these cells, the potassium channel opener pinacidil (10 micromol/L) did not prevent Ca2+ loading (from 96+/-3 nmol/L before to 233+/-12 nmol/L after reoxygenation) or evoked membrane current. Cotransfection with Kir6.2/SUR2A genes, which encode cardiac KATP channel subunits, resulted in a cellular phenotype that, in the presence of pinacidil (10 micromol/L), expressed K+ current and gained resistance to hypoxia-reoxygenation (Ca2+ concentration from 99+/-7 to 127+/-11 nmol/L; P>0.05). Both properties were abolished by the KATP channel blocker glyburide (1 micromol/L). In COS-7 cells transfected with individual channel subunits Kir6.2 or SUR2A, which alone do not form functional cardiac KATP channels, pinacidil did not protect against hypoxia-reoxygenation. CONCLUSIONS: The fact that transfer of cardiac KATP channel subunits protected natively KATP channel deficient cells provides direct evidence that the cardiac KATP channel protein complex harbors intrinsic cytoprotective properties. These findings validate the concept that targeting cardiac KATP channels should be considered a valuable approach to protect the myocardium against injury.

Adenosine Triphosphate↗
PubMed1998

Diadenosine 5',5"-P1,P5-pentaphosphate harbors the properties of a signaling molecule in the heart.

Dinucleotide polyphosphates (ApnA) have emerged as signaling molecules in rapidly dividing cells. The presence and role of Ap5A in the heart remain unknown. Here, we report that the myocardium contains abundant amounts of diadenosine 5',5"-P1,P5-pentaphosphate (Ap5A), a member of the ApnA family. Ischemia induced 10-fold decrease in the myocardial concentration of Ap5A. A target of Ap5A action was identified to be the cardiac ATP-sensitive K+ (K(ATP)) channel, a metabolism-sensitive ion conductance activated in ischemia. At levels found in hearts prior to ischemia, Ap5A maintained a low probability of K(ATP) channel opening, but at levels found in hearts following ischemia, Ap5A allowed a high probability of K(ATP) channel opening. Taken together, the present data suggest that Ap5A harbors the properties of a signaling molecule involved in the cardiac response to metabolic stress.

Animals↗
PubMed1998

Operative condition-dependent response of cardiac ATP-sensitive K+ channels toward sulfonylureas.

A defining property of ATP-sensitive K+ (K[ATP]) channels is inhibition by sulfonylurea drugs, yet the response of cardiac K[ATP] channels toward sulfonylureas during myocardial ischemia is not consistent. Altered channel sensitivity toward sulfonylureas has, in part, been ascribed to antagonism by cytosolic nucleotide diphosphates, although the mechanism of interaction remains unclear. Herein, in inside-out patches excised from cardiomyocytes, we observed a dual response of K[ATP] channels toward the sulfonylurea drug, glyburide, in the presence of cytosolic UDP. Specifically, glyburide failed to inhibit spontaneous K[ATP] channel activity in the presence of UDP but inhibited UDP-induced channel activity after rundown of spontaneous channel openings. Such behavior of K[ATP] channels cannot be explained by differences in the level of channel activity or by UDP-induced displacement of glyburide. Rather, the dual response toward the sulfonylurea could be attributed to a property of K[ATP] channels to switch between operative conditions (spontaneous versus UDP-induced) each associated with a distinct responsiveness toward ligands. Conversion of post-rundown K[ATP] channels to the spontaneously operative channel condition, by Mg-ATP, restored the ability of UDP to antagonize the inhibitory action of glyburide lost after rundown, suggesting that the response of the channel to glyburide is phosphorylation dependent. The existence of distinct operative conditions of cardiac K[ATP] channels could be the basis for the inconsistent response of the channel toward sulfonylurea drugs and should be considered when sulfonylureas are used to implicate the opening of K[ATP] channels in the myocardium.

Adenosine Triphosphate↗
PubMed1998

Adenosine prevents K+-induced Ca2+ loading: insight into cardioprotection during cardioplegia.

In clinical practice, hyperkalemic cardioplegia induces sarcolemmic depolarization, and therefore is used to arrest the heart during open heart operations. However, the elevated concentration of K+ that is present in cardioplegic solutions promotes intracellular Ca2+ loading, which could aggravate ventricular dysfunction after cardiac operations. This review highlights recent findings that have established, at the single cell level, the protective action of adenosine against hyperkalemia-induced Ca2+ loading. When it was added to hyperkalemic cardioplegic solutions, adenosine, at millimolar concentrations and through a direct action on ventricular cardiomyocytes, prevented K+-induced Ca2+ loading. This action of adenosine required the activation of protein kinase C, and it was effective only in cardiomyocytes with low diastolic Ca2+ levels. Of importance, adenosine did not diminish the magnitude of K+-induced membrane depolarization, allowing unimpeded cardiac arrest. Taken together, these findings provide direct support for the idea that adenosine is valuable when used as an adjunct to hyperkalemic cardioplegia. This idea has emerged from previous clinical studies that have shown improvement of the clinical outcome after cardiac operations when adenosine or related substances were used to supplement cardioplegic solutions. Further studies are required to define more precisely the mechanism of action of adenosine, and the conditions that may determine the efficacy of adenosine as a cytoprotective supplement to cardioplegia.

Adenosine↗