Modifying the first minute of reperfusion: potential for myocardial salvage.
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Animals↗
Biomedical subjects
Gregory J Wilson
Publications and source records attributed to Gregory J Wilson.
Parallel imaging in MR angiography.
The recently developed techniques of parallel imaging with phased array coils are rapidly becoming accepted for magnetic resonance angiography (MRA) applications. This article reviews the various current parallel imaging techniques and their application to MRA. The increased scan efficiency provided by parallel imaging allows increased temporal or spatial resolution, and reduction of artifacts in contrast-enhanced MRA (CE-MRA). Increased temporal resolution in CE-MRA can be used to reduce the need for bolus timing and to provide hemodynamic information helpful for diagnosis. In addition, increased spatial resolution (or volume coverage) can be acquired in a breathhold (eg, in renal CE-MRA), or in otherwise limited clinically acceptable scan durations. The increased scan efficiency provided by parallel imaging has been successfully applied to CE-MRA as well as other MRA techniques such as inflow and phase contrast imaging. The large signal-to-noise ratio available in many MRA techniques lends these acquisitions to increased scan efficiency through parallel imaging.
Contrast Media↗
Molecular dissection of the inward rectifier potassium current (IK1) in rabbit cardiomyocytes: evidence for heteromeric co-assembly of Kir2.1 and Kir2.2.
Cardiac inward rectifier K+ currents (IK1) play an important role in maintaining resting membrane potential and contribute to late phase repolarization. Members of the Kir2.x channel family appear to encode for IK1. The purpose of this study was to determine the molecular composition of cardiac IK1 in rabbit ventricle. Western blots revealed that Kir2.1 and Kir2.2, but not Kir2.3, are expressed in rabbit ventricle. Culturing rabbit myocytes resulted in an approximately 50% reduction of IK1 density after 48 or 72 h in culture which was associated with an 80% reduction in Kir2.1, but no change in Kir2.2, protein expression. Dominant-negative (DN) constructs of Kir2.1, Kir2.2 and Kir2.3 were generated and tested in tsA201 cells. Adenovirus-mediated over-expression of Kir2.1dn, Kir2.2dn or Kir2.1dn plus Kir2.2dn in cultured rabbit ventricular myocytes reduced IK1 density equally by 70% 72 h post-infection, while AdKir2.3dn had no effect, compared to green fluorescent protein (GFP)-infected myocytes. Previous studies indicate that the [Ba2+] required for half-maximum block (IC50) differs significantly between Kir2.1, Kir2.2 and Kir2.3 channels. The dependence of IK1 on [Ba2+] revealed a single binding isotherm which did not change with time in culture. The IC50 for block of IK1 was also unaffected by expression of the different DN genes after 72 h in culture. Taken together, these results demonstrate functional expression of Kir2.1 and Kir2.2 in rabbit ventricular myocytes and suggest that macroscopic IK1 is predominantly composed of Kir2.1 and Kir2.2 heterotetramers.
Adenoviridae↗
Enhanced cell volume regulation: a key protective mechanism of ischemic preconditioning in rabbit ventricular myocytes.
Accumulation of osmotically active metabolites, which create an osmotic gradient estimated at ~60 mOsM, and cell swelling are prominent features of ischemic myocardial cell death. This study tests the hypothesis that reduction of ischemic swelling by enhanced cell volume regulation is a key mechanism in the delay of ischemic myocardial cell death by ischemic preconditioning (IPC). Experimental protocols address whether: (i) IPC triggers a cell volume regulation mechanism that reduces cardiomyocyte swelling during subsequent index ischemia; (ii) this reduction in ischemic cell swelling is sufficient in magnitude to account for the IPC protection; (iii) the molecular mechanism that mediates IPC also mediates cell volume regulation. Two experimental models with rabbit ventricular myocytes were studied: freshly isolated pelleted myocytes and 48-h cultured myocytes. Myocytes were preconditioned either by distinct short simulated ischemia (SI)/simulated reperfusion protocols (IPC), or by subjecting myocytes to a pharmacological preconditioning (PPC) protocol (1 microM calyculin A, or 1 microM N(6)-2-(4-aminophenyl)ethyladenosine (APNEA), prior to subjecting them to either different durations of long SI or 30 min hypo-osmotic stress. Cell death (percent blue square myocytes) was monitored by trypan blue staining. Cell swelling was determined by either the bromododecane cell flotation assay (qualitative) or video/confocal microscopy (quantitative). Simulated ischemia induced myocyte swelling in both the models. In pelleted myocytes, IPC or PPC with either calyculin A or APNEA produced a marked reduction of ischemic cell swelling as determined by the cell floatation assay. In cultured myocytes, IPC substantially reduced ischemic cell swelling (P < 0.001). This IPC effect on ischemic cell swelling was related to an IPC and PPC (with APNEA) mediated triggering of cell volume regulatory decrease (RVD). IPC and APNEA also significantly (P < 0.001) reduced hypo-osmotic cell swelling. This IPC and APNEA effect was blocked by either adenosine receptor, PKC or Cl(-) channel inhibition. The osmolar equivalent for IPC protection approximated 50-60 mOsM, an osmotic gradient similar to the estimated ischemic osmotic load for preconditioned and non-preconditioned myocytes. The results suggest that cell volume regulation is a key mechanism that accounts for most of the IPC protection in cardiomyocytes.
Animals↗
Pharmacological preconditioning in rabbit myocardium is blocked by chloride channel inhibition.
OBJECTIVES: We have recently proposed that chloride (Cl(-)) channels contribute to ischemic preconditioning (IPC) in the myocardium. To further evaluate this hypothesis, we investigated the role of Cl(-) channels in pharmacological preconditioning. METHODS: Isolated rabbit cardiomyocytes and isolated buffer-perfused rabbit hearts were initially preconditioned with a 10 min exposure to either an adenosine receptor agonist [2-chloro-N(6)-cyclopentyladenosine (CCPA, 200 nM) and/or N(6)-2-(4-aminophenyl)ethyladenosine (APNEA, 1 microM)] or the PKC activator phorbol 12-myristate 13-acetate (PMA, 1 microM) followed by a 10 or 20 min washout or not preconditioned (control). Cardiomyocytes or whole hearts were then subjected to prolonged ischemic period (45 min simulated ischemia or 40 min of regional myocardial ischemia, respectively) followed by 60 min reperfusion (resuspension in oxygenated medium or release of the transient coronary occlusion, respectively). RESULTS: Indanyloxyacetic acid 94, a selective Cl(-) channel inhibitor that produced substantial inhibition of the regulatory volume decrease (RVD) when given at 10 microM concentration in cultured cardiomyocytes, was administered before ischemia to block RVD through Cl(-) channel inhibition. CCPA, APNEA and PMA significantly (P<0.01) reduced the % of dead cardiomyocytes (by trypan blue staining) after 45 min SI/60 min SR, as compared to controls, while IAA-94 abolished this protection but did not affect PKCepsilon translocation by IPC. We confirmed that IAA-94 blocked IPC-, APNEA- and PMA-induced protection against infarction in the isolated heart model. CONCLUSIONS: These findings support our contention that Cl(-) channels are downstream effectors of IPC.
Adenosine↗
Inhibition of calcineurin and sarcolemmal Ca2+ influx protects cardiac morphology and ventricular function in K(v)4.2N transgenic mice.
BACKGROUND: Cardiac-targeted expression of truncated K(v)4.2 subunit (K(v)4.2N) reduces transient outward current (I(to)) density, prolongs action potentials (APs), and enhances contractility in 3- to 4-week-old transgenic mice. By 13 to 15 weeks of age, these mice develop severely impaired cardiac function and signs of heart failure. In this study, we examined whether augmented contractility in K(v)4.2N mice results from elevations in intracellular calcium ([Ca2+]i) secondary to AP prolongation and investigated the putative roles of calcineurin activation in heart disease development of K(v)4.2N mice. METHODS AND RESULTS: At 3 to 4 weeks of age, L-type Ca2+ influx and peak [Ca2+]i were significantly elevated in K(v)4.2N myocytes compared with control because of AP prolongation. Cardiac calcineurin activity was also significantly elevated in K(v)4.2N mice by 5 weeks of age relative to controls and increased progressively as heart disease developed. This was associated with activation of protein kinase C (PKC)-alpha and PKC-theta but not PKC-epsilon, as well as increases in beta-myosin heavy chain (beta-MHC) and reductions in sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA)-2a expression. Treatment with either cyclosporin A or verapamil prevented increases in heart weight to body weight ratios, interstitial fibrosis, impaired contractility, PKC activation, and changes in the expression patterns of beta-MHC and SERCA2a. CONCLUSIONS: Our results demonstrate that AP prolongation caused by I(to) reduction results in enhanced Ca2+ cycling and hypercontractility in mice and suggests that elevations in [Ca2+]i via I(Ca,L) and activation of calcineurin play a central role in disease development after I(to) reduction using the K(v)4.2N construct.
Action Potentials↗
Utilizing SENSE to achieve lower station sub-millimeter isotropic resolution and minimal venous enhancement in peripheral MR angiography.
PURPOSE: To use the parallel imaging technique, sensitivity encoding (SENSE), to increase spatial resolution and decrease venous contamination in peripheral magnetic resonance angiography (MRA). MATERIALS AND METHODS: Moving table, single-bolus peripheral contrast-enhanced (CE) -MRA was performed on nine patients. Manual table movement combined with SENSE in the upper station allowed for more rapid overall scan coverage such that acquisition of the lower station began 34 seconds after aortic contrast arrival. True sub- millimeter isotropic resolution was achieved in the lower station. RESULTS: Diagnostic MR angiograms of all three stations were obtained in all nine patients. Venous enhancement did not confound interpretation in any case. Sub-millimeter lower station resolution provided excellent vascular detail. CONCLUSION: Decreased delay time between upper and lower station acquisition in single bolus peripheral MR angiograms, now possible using parallel imaging techniques, combined with lower station sub-millimeter resolution may decrease venous contamination and increase overall interpretability, thus increasing clinical acceptance of peripheral MRA.
Humans↗
Motion of the distal renal artery during three-dimensional contrast-enhanced breath-hold MRA.
PURPOSE: To study the potential detrimental effects of renal motion on breath-hold three-dimensional contrast-enhanced (CE) magnetic resonance angiography (MRA). MATERIALS AND METHODS: A computer model simulating linear motion was applied to MRA pulse sequences. Subsequently, to study whether renal motion was present, 24 patients being evaluated for possible renovascular hypertension underwent a breath-hold nonenhanced single slice two-dimensional dynamic turbo field-echo magnetic resonance imaging (MRI) scan with a typical duration of 32 seconds. This sequence was followed by breath-hold three-dimensional CE renal MRA. CE-MRA images were evaluated by two independent observers. RESULTS: The computer model revealed linear renal motion to cause artifacts. The severity of these artifacts correlated with velocity. Significant (P < 0.001) near linear cranial motion of the kidneys and diaphragm during a sustained breath-hold was found for the right kidney, left kidney, right diaphragm, and left diaphragm (0.26 +/- 0.21 mm/second, 0.25 +/- 0.23 mm/second, 0.43 +/- 0.43 mm/second, and 0.29 +/- 0.33 mm/second [mean +/- SD], respectively). CE-MRA images showed artifacts of the distal renal artery that corroborated the computer model findings. CONCLUSION: The observed cranial motion of the kidneys during a breath-hold adversely affects distal renal artery image quality on three-dimensional CE-MRA and jeopardizes reliable clinical evaluation. Shortening scan time may be beneficial for decreasing image degradation caused by this phenomenon.
Adult↗
A single mutation in the carboxy terminus of reovirus outer-capsid protein sigma 3 confers enhanced kinetics of sigma 3 proteolysis, resistance to inhibitors of viral disassembly, and alterations in sigma 3 structure.
Mammalian reoviruses undergo acid-dependent proteolytic disassembly within endosomes, resulting in formation of infectious subvirion particles (ISVPs). ISVPs are obligate intermediates in reovirus disassembly that mediate viral penetration into the cytoplasm. The initial biochemical event in the reovirus disassembly pathway is the proteolysis of viral outer-capsid protein sigma 3. Mutant reoviruses selected during persistent infection of murine L929 cells (PI viruses) demonstrate enhanced kinetics of viral disassembly and resistance to inhibitors of endocytic acidification and proteolysis. To identify sequences in sigma 3 that modulate acid-dependent and protease-dependent steps in reovirus disassembly, the sigma 3 proteins of wild-type strain type 3 Dearing; PI viruses L/C, PI 2A1, and PI 3-1; and four novel mutant sigma 3 proteins were expressed in insect cells and used to recoat ISVPs. Treatment of recoated ISVPs (rISVPs) with either of the endocytic proteases cathepsin L or cathepsin D demonstrated that an isolated tyrosine-to-histidine mutation at amino acid 354 (Y354H) enhanced sigma 3 proteolysis during viral disassembly. Yields of rISVPs containing Y354H in sigma3 were substantially greater than those of rISVPs lacking this mutation after growth in cells treated with either acidification inhibitor ammonium chloride or cysteine protease inhibitor E64. Image reconstructions of electron micrographs of virus particles containing wild-type or mutant sigma 3 proteins revealed structural alterations in sigma 3 that correlate with the Y354H mutation. These results indicate that a single mutation in sigma 3 protein alters its susceptibility to proteolysis and provide a structural framework to understand mechanisms of sigma 3 cleavage during reovirus disassembly.
Capsid↗
A novel rabbit model of variably compensated complete heart block.
Complete heart block (CHB) provides a useful substrate for study of bradycardia-dependent ventricular arrhythmias and cardiac function. Existing CHB animal models are limited by surgical recovery time and reliance on intrinsic escape rhythms. We describe a novel closed-chest rabbit model of CHB involving transcatheter radiofrequency (RF) atrioventricular (AV) node ablation and ventricular rate control with chronic transvenous pacing. Permanent CHB was achieved in 34 of 38 attempts overall. Procedural mortality due to cardiac tamponade (n = 2), airway complications (n = 2), and unknown causes (n = 5) occurred in nine animals. Survivors with CHB (n = 28) were maintained for < or = 22 days, during which there were three late deaths related to infection (n = 1) or respiratory distress (n = 2). None of the survivors with CHB showed recovery of AV conduction or pacemaker capture loss during chronic ventricular pacing at about one-half normal sinus rates, and 25 animals surviving to death showed no overt signs of hemodynamic compromise such as lethargy, poor feeding, or respiratory distress. This approach provides a reproducible nonsurgical CHB model with adjustable ventricular rate control.
Animals↗
Biodegradation of methyl tert-butyl ether and BTEX at varying hydraulic retention times.
The feasibility of biologically degrading methyl tert-butyl ether (MTBE)-contaminated groundwater is dependent on the ability to degrade MTBE and its byproducts in the presence of other gasoline contaminants. This study investigates a mixed culture degrading both MTBE and benzene-toluene-ethylbenzene-xylene (BTEX) in a continuous-flow reactor with a biomass retention system (porous pot) at varying hydraulic retention times (HRTs). The reactor degraded both MTBE and BTEX simultaneously to less than the U.S. Environmental Protection Agency's drinking water standards and recommendations at an HRT of 3.76 days. Methyl tert-butyl ether was degraded from 75 mg/L to less than 1 microg/L and each BTEX compound was degraded from 17 mg/L to less than 1 microg/L. Effluent concentrations of MTBE and BTEX increased as the HRT was decreased from 3.76 to 0.52 days, but remained lower than drinking water limits. The highest MTBE effluent concentration was at 0.52 days and continued to average less than 10 microg/L. Although tert-butyl alcohol (TBA) is commonly sited as a degradation byproduct of MTBE, it remained lower than 1 microg/L throughout all reactor operation periods. The MTBE and BTEX observed yield coefficients for the reactor ranged from 0.11 to 0.16 mg biomass/mg MTBE and BTEX, with the rate increasing with increased HRT. Degradation rates from the reactor were compared to results from batch studies with the same culture on MTBE and TBA alone and in the presence of BTEX. Results of batch studies showed that BTEX was not required for this culture to degrade MTBE. The presence of BTEX only had an effect on the rate of MTBE degradation at the highest concentration, while BTEX significantly delayed the degradation of TBA at all concentrations. Batch studies also showed that the rate of degradation of TBA was higher with and without BTEX than the rate of degradation of MTBE, explaining the lack of high levels of TBA in the reactor.
Benzene↗