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David C Warltier

Publications and source records attributed to David C Warltier.

At least 19 recordsLinked to original sources
PubMed2007

Isoflurane preconditioning uncouples mitochondria and protects against hypoxia-reoxygenation.

Ischemic cardiac injury can be substantially alleviated by exposing the heart to pharmacological agents such as volatile anesthetics before occurrence of ischemia-reperfusion. A hallmark of this preconditioning phenomenon is its memory, when cardioprotective effects persist even after removal of preconditioning stimulus. Since numerous studies pinpoint mitochondria as crucial players in protective pathways of preconditioning, the aim of this study was to investigate the effects of preconditioning agent isoflurane on the mitochondrial bioenergetic phenotype. Endogenous flavoprotein fluorescence, an indicator of mitochondrial redox state, was elevated to 195 +/- 16% of baseline upon isoflurane application in intact cardiomyocytes, indicating more oxidized state of mitochondria. Isoflurane treatment also elicited partial dissipation of mitochondrial transmembrane potential, which remained depolarized even after anesthetic withdrawal (tetramethylrhodamine fluorescence intensity declined to 83 +/- 3 and 81 +/- 7% of baseline during isoflurane exposure and washout, respectively). Mild uncoupling, with preserved ATP synthesis, was also detected in mitochondria that were isolated from animals that had been previously preconditioned by isoflurane in vivo, revealing its memory nature. These mitochondria, after exposure to hypoxia and reoxygenation, exhibited better preserved respiration and ATP synthesis compared with mitochondria from nonpreconditioned animals. Partial mitochondrial depolarization was paralleled by a diminished Ca(2+) uptake into isoflurane-treated mitochondria, as indicated by the reduced increment in rhod-2 fluorescence when mitochondria were challenged with increased Ca(2+) (180 +/- 24 vs. 258 +/- 14% for the control). In conclusion, isoflurane preconditioning elicits partial mitochondrial uncoupling and reduces mitochondrial Ca(2+) uptake. These effects are likely to reduce the extent of the mitochondrial damage after the hypoxic stress.

Adenosine Diphosphate↗
PubMed2006

Alterations in regional vascular geometry produced by theoretical stent implantation influence distributions of wall shear stress: analysis of a curved coronary artery using 3D computational fluid dynamics modeling.

BACKGROUND: The success of stent implantation in the restoration of blood flow through areas of vascular narrowing is limited by restenosis. Several recent studies have suggested that the local geometric environment created by a deployed stent may influence regional blood flow characteristics and alter distributions of wall shear stress (WSS) after implantation, thereby rendering specific areas of the vessel wall more susceptible to neointimal hyperplasia and restenosis. Stents are most frequently implanted in curved vessels such as the coronary arteries, but most computational studies examining blood flow patterns through stented vessels conducted to date use linear, cylindrical geometric models. It appears highly probable that restenosis occurring after stent implantation in curved arteries also occurs as a consequence of changes in fluid dynamics that are established immediately after stent implantation. METHODS: In the current investigation, we tested the hypothesis that acute changes in stent-induced regional geometry influence distributions of WSS using 3D coronary artery CFD models implanted with stents that either conformed to or caused straightening of the primary curvature of the left anterior descending coronary artery. WSS obtained at several intervals during the cardiac cycle, time averaged WSS, and WSS gradients were calculated using conventional techniques. RESULTS: Implantation of a stent that causes straightening, rather than conforms to the natural curvature of the artery causes a reduction in the radius of curvature and subsequent increase in the Dean number within the stented region. This straightening leads to modest skewing of the velocity profile at the inlet and outlet of the stented region where alterations in indices of WSS are most pronounced. For example, time-averaged WSS in the proximal portion of the stent ranged from 8.91 to 11.7 dynes/cm2 along the pericardial luminal surface and 4.26 to 4.88 dynes/cm2 along the myocardial luminal surface of curved coronary arteries as compared to 8.31 dynes/cm2 observed throughout the stented region of a straight vessel implanted with an equivalent stent. CONCLUSION: The current results predicting large spatial and temporal variations in WSS at specific locations in curved arterial 3D CFD simulations are consistent with clinically observed sites of restenosis. If the findings of this idealized study translate to the clinical situation, the regional geometry established immediately after stent implantation may predispose portions of the stented vessel to a higher risk of neointimal hyperplasia and subsequent restenosis.

Animals↗
PubMed2006

Role of Erk1/2, p70s6K, and eNOS in isoflurane-induced cardioprotection during early reperfusion in vivo.

PURPOSE: Administration of isoflurane during early reperfusion after prolonged coronary artery occlusion decreases myocardial infarct size by activating phosphatidylinositol-3-kinase (PI3K) signal transduction. The extracellular signal-related kinases (Erk1/2) represent a redundant mechanism by which signaling elements downstream from PI3K, including 70-kDA ribosomal protein s6 kinase (p70s6K) and endothelial nitric oxide synthase (eNOS), may be activated to reduce reperfusion injury. We tested the hypothesis Erk1/2, p70s6K, and eNOS mediate isoflurane-induced postconditioning in rabbit myocardium in vivo. METHODS: Barbiturate-anesthetized rabbits (n = 78) instrumented for measurement of systemic hemodynamics were subjected to a 30-min coronary occlusion followed by three hours reperfusion. Rabbits were randomly assigned to receive 0.9% saline (control), the Erk1/2 inhibitor PD 098059 (2 mg x kg(-1)), the p70s6K inhibitor rapamycin (0.25 mg x kg(-1)), the nonselective nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME; 10 mg x kg(-1)), the selective inducible NOS antagonist aminoguanidine hydrochloride (AG, 300 mg x kg(-1)), or the selective neuronal NOS inhibitor 7-nitroindazole (7-NI, 50 mg x kg(-1)) in the presence or absence of 1.0 minimum alveolar concentration isoflurane administered for three minutes before and two minutes after reperfusion. RESULTS: Brief exposure to 1.0 minimum alveolar concentration isoflurane reduced (P < 0.05) infarct size (21 +/- 4% [mean +/- SD] of left ventricle area at risk, respectively; triphenyltetrazolium staining) as compared to control (41 +/- 5%). PD 098059, rapamycin, and L-NAME, but not AG nor 7-NI, abolished the protection produced by isoflurane. CONCLUSION: The results suggest that the protective effects of isoflurane against infarction during early reperfusion are mediated by Erk1/2, p70s6K, and eNOS in vivo.

Anesthetics, Inhalation↗
PubMed2006

Mechanism of cardiac sarcolemmal adenosine triphosphate-sensitive potassium channel activation by isoflurane in a heterologous expression system.

BACKGROUND: Activation of the cardiac sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channel during metabolic stress initiates cellular events that preserve cardiac performance. Previous studies showed that halogenated anesthetics prime KATP channels under whole cell voltage clamp and act in intracellular pH (pHi)-dependent manner on KATP channels in excised membrane patches. However, it is not known how halogenated anesthetics interact with these channels. METHODS: The authors evaluated the effect of pHi and isoflurane on the KATP channel subunits, the pore-forming inward rectifier Kir6.2, and the regulatory sulfonylurea receptor SUR2A, using HEK293 cells as a heterologous expression system. Single channel activity was recorded in the inside-out patch configuration. RESULTS: At pHi 7.4, isoflurane had negligible effect on activity of wild-type Kir6.2/SUR2A, but at pHi 6.8, the channel open probability was increased by isoflurane (0.177 +/- 0.077 to 0.364 +/- 0.164). By contrast, the open probability of truncated Kir6.2DeltaC26, which forms a functional channel without SUR2A, was attenuated by isoflurane at both pHi 7.4 and pHi 6.8. Coexpression of Kir6.2DeltaC26 with SUR2A restored pHi sensitivity of channel activation by isoflurane. Site-directed mutagenesis within the Walker motifs of SUR2A abolished isoflurane activation of KATP channel at pHi 6.8. In addition, the pancreatic-type channels expressing sulfonylurea receptor SUR1 could not be activated by isoflurane. CONCLUSIONS: The nucleotide binding domains of SUR2A play a crucial role in isoflurane facilitation of the KATP channel activity at moderately acidic pHi as would occur during early ischemia. These findings support direct and differential interaction of isoflurane with the subunits of the cardiac sarcolemmal KATP channel.

ATP-Binding Cassette Transporters↗
PubMed2006

Cardioprotection by volatile anesthetics: new applications for old drugs?

PURPOSE OF REVIEW: Pharmacological interventions may play a prominent role in reducing organ damage in response to physiologic stress. A growing body of evidence indicates that volatile anesthetics exert protective effects against ischemia-reperfusion injury in vivo. Administration of volatile anesthetics before prolonged coronary artery occlusion and reperfusion has been shown to produce cardioprotection, a phenomenon termed anesthetic-induced preconditioning. Endogenous signal transduction proteins, reactive oxygen species, mitochondria, and ion channels have been implicated in anesthetic-induced preconditioning, and new data regarding the triggering and effector roles for these various components have been discovered that advance our understanding of the mechanisms responsible for anesthetic-induced preconditioning. This review will update and integrate these recent data into the current mechanistic model of anesthetic-induced preconditioning. RECENT FINDINGS: Despite a wealth of data from animal studies, the mechanism by which preconditioning with volatile anesthetics alleviates ischemic injury remains incompletely understood. Recent data have identified important interactions between reactive oxygen species and key intracellular signal transduction enzymes and proteins implicated in anesthetic-induced preconditioning. SUMMARY: This review highlights the major recent findings examining mechanisms of volatile anesthetic cardioprotection.

Anesthetics, Inhalation↗
PubMed2006

Inhibition of glycogen synthase kinase enhances isoflurane-induced protection against myocardial infarction during early reperfusion in vivo.

Inhibition of glycogen synthase kinase (GSK)-beta protects against ischemia-reperfusion injury. Brief exposure to isoflurane before and during early reperfusion after coronary artery occlusion also protects against infarction. Whether GSK-beta mediates this action is unknown. We tested the hypothesis that GSK inhibition enhances isoflurane-induced postconditioning. Rabbits (n = 88; 6 to 7 per group) subjected to a 30-min coronary occlusion followed by 3 h reperfusion received saline, isoflurane (0.5 or 1.0 minimum alveolar concentration [MAC]) administered for 3 min before and 2 min after reperfusion, the selective GSK inhibitor SB216763 (SB21; 0.2 or 0.6 mg/kg), or 0.5 MAC isoflurane plus 0.2 mg/kg SB21. Other groups of rabbits pretreated with phosphatidylinositol-3 kinase (PI3K) inhibitor wortmannin (0.6 mg/kg), 70-kDa ribosomal protein s6 kinase (p70s6K) inhibitor rapamycin (0.25 mg/kg), or mitochondrial permeability transition pore (mPTP) opener atractyloside (5 mg/kg) received 0.6 mg/kg SB21 or 0.5 MAC isoflurane plus 0.2 mg/kg SB21. Additional groups received the mPTP inhibitor, cyclosporin A (5 mg/kg), plus 0.2 mg/kg SB21 with or without atractyloside pretreatment. Isoflurane (1.0 but not 0.5 MAC) and SB21 (0.6 but not 0.2 mg/kg) reduced (P < 0.05) infarct size (21% +/- 5%, 44% +/- 7%, 23% +/- 4%, and 46% +/- 2%, respectively, of left ventricular area at risk, mean+/- sd; triphenyltetrazolium staining) as compared with control (42% +/- 6%). Isoflurane (0.5 MAC) plus 0.2 mg/kg SB21 and cyclosporin A plus 0.2 mg/kg SB21 produced similar degrees of protection (24% +/- 4% and 27% +/- 6%, respectively). Atractyloside but not wortmannin or rapamycin abolished protection produced by 0.6 mg/kg SB21 and 0.5 MAC isoflurane plus 0.2 mg/kg SB21. Thus, GSK inhibition enhances isoflurane-induced protection against infarction during early reperfusion via a mPTP-dependent mechanism.

Animals↗
PubMed2006

The influence of B-cell lymphoma 2 protein, an antiapoptotic regulator of mitochondrial permeability transition, on isoflurane-induced and ischemic postconditioning in rabbits.

Brief exposure to isoflurane or repetitive, transient ischemia during early reperfusion after prolonged coronary artery occlusion protects against myocardial infarction by inhibiting the mitochondrial permeability transition pore (mPTP). Inhibition of mPTP during delayed ischemic preconditioning occurred concomitant with enhanced expression of the antiapoptotic protein B cell lymphoma-2 (Bcl-2). We tested the hypothesis that Bcl-2 mediates myocardial protection by isoflurane or brief ischemic episodes during reperfusion in rabbits (n = 91) subjected to a 30-min left anterior descending coronary artery occlusion followed by 3 h reperfusion. Rabbits received 0.9% saline, isoflurane (0.5 or 1.0 minimum alveolar concentration, MAC) administered for 3 min before and 2 min after reperfusion, 3 cycles of postconditioning ischemia (10 or 20 s each) during early reperfusion, 0.5 MAC isoflurane plus 3 cycles of postconditioning ischemia (10 s), or the direct mPTP inhibitor cyclosporin A (CsA, 10 mg/kg) in the presence or absence of the selective Bcl-2 inhibitor HA14-1 (2 mg/kg, i.p.). Isoflurane (1.0, but not 0.5, MAC) and postconditioning ischemia (20 s but not 10 s) significantly (P < 0.05) reduced infarct size (mean +/- sd, 21% +/- 4%, 43% +/- 7%, 19% +/- 7%, and 39% +/- 11%, respectively, of left ventricular area at risk) as compared with control (44% +/- 4%). Isoflurane (0.5 MAC) plus 10 s postconditioning ischemia and CsA alone also exerted protection. HA14-1 alone did not affect infarct size nor block protection produced by CsA but abolished reductions in infarct size caused by 1.0 MAC isoflurane, 20 s postconditioning ischemia, and 0.5 MAC isoflurane plus 10 s postconditioning ischemia. The results suggest that Bcl-2 mediates isoflurane-induced and ischemic postconditioning by indirectly modulating mPTP activity in vivo.

Animals↗
PubMed2006

Extracellular signal-regulated kinases trigger isoflurane preconditioning concomitant with upregulation of hypoxia-inducible factor-1alpha and vascular endothelial growth factor expression in rats.

INTRODUCTION: Extracellular signal-related kinases 1 and 2 (Erk1/2) are mitogen-activated protein kinases that have been implicated in anesthetic preconditioning; but whether Erk1/2 triggers or mediates this beneficial effect and the mechanisms by which Erk1/2 produces cardioprotection are unknown. We tested the hypothesis that isoflurane preconditioning is triggered by Erk1/2 concomitant with upregulation of hypoxia-inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) expression in rats instrumented for hemodynamic measurement and subjected to a 30-min coronary artery occlusion and 2-h reperfusion. METHODS: Rats randomly received IV 0.9% saline (control) or isoflurane (1.0 minimum alveolar concentration administered for 30 min and discontinued 15 min [memory period] before coronary occlusion) in the absence or presence of the selective Erk1/2 inhibitor PD 098059 (1 mg/kg in dimethylsulfoxide administered IV either 3 min before exposure to isoflurane [trigger] or 3 min after discontinuation of the drug [mediator]). Additional rabbits were pretreated with dimethylsulfoxide alone. Left ventricular tissue samples were obtained at selected intervals from additional groups of rats for Western immunoblot analysis of phospho-Erk1/2, HIF-1alpha, and VEGF protein expression. RESULTS: Isoflurane significantly (P < 0.05) reduced infarct size (41% +/- 8% of the left ventricular area at risk; triphenyltetrazolium chloride staining) as compared with control (59% +/- 4%). PD 098059 administered before, but not after, isoflurane abolished this cardioprotection (61% +/- 5% and 42% +/- 9%, respectively). Isoflurane-induced increases in phospho-Erk1/2, HIF-1alpha, and VEGF expression were also inhibited by PD 098059 pretreatment. CONCLUSIONS: The results indicate that Erk1/2 triggers isoflurane preconditioning concomitant with HIF-1alpha and VEGF upregulation in vivo.

Anesthetics, Inhalation↗
PubMed2006

Gender-specificity of delayed preconditioning by isoflurane in rabbits: potential role of endothelial nitric oxide synthase.

INTRODUCTION: Female gender confers cardioprotection against ischemia-reperfusion injury, in part because estrogen enhances nitric oxide production by endothelial nitric oxide synthase (eNOS). Whether ischemic preconditioning occurs in females remains controversial. Delayed myocardial preconditioning by isoflurane is mediated by eNOS in male rabbits, but whether females are similarly protected by isoflurane is unknown. We tested the hypothesis that gender-specific reductions in myocardial infarct size occur in female rabbits, but that this inherent cardioprotection abrogates further beneficial effects of isoflurane-induced delayed preconditioning. METHODS: Rabbits (n = 115) underwent a 30 min coronary artery occlusion and 3 h reperfusion with or without a 2 h administration of 1.0 minimum alveolar concentration isoflurane one day before experimentation. Rabbits received saline or a nonselective, selective inducible, or selective neuronal NOS inhibitor [N-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), aminoguanidine (AG, 300 mg/kg), or 7-nitroindazole (7-NI, 50 mg/kg), respectively]. RESULTS: Isoflurane reduced infarct size in males (mean+/- sd, 26 +/- 5% of the left ventricular area at risk) versus saline (45 +/- 2%). L-NAME, but not AG or 7-NI, abolished isoflurane-induced protection in males (41 +/- 9, 24 +/- 4 and 22 +/- 2%, respectively). Infarct size was reduced, and eNOS protein expression was greater, in female versus male rabbits. Infarct size was unchanged in female rabbits with, versus without, isoflurane pretreatment (27 +/- 9 and 27 +/- 10%, respectively). L-NAME, but not AG or 7-NI, increased infarct size with or without isoflurane pretreatment in females. CONCLUSIONS: Female gender-induced reductions in infarct size are mediated by eNOS, but remote isoflurane exposure (1.0 MAC) before ischemia and reperfusion does not produce additional cardioprotection in vivo.

Anesthetics, Inhalation↗
PubMed2006

Inhibition of apoptotic protein p53 lowers the threshold of isoflurane-induced cardioprotection during early reperfusion in rabbits.

INTRODUCTION: Exposure to isoflurane before and during early reperfusion protects against myocardial infarction by activating phosphatidylinositol-3-kinase (PI3K)-mediated signaling. The apoptotic protein, p53, is regulated by PI3K, and inhibition of p53 protects against ischemic injury. We tested the hypothesis that p53 inhibition lowers the threshold of isoflurane-induced postconditioning in vivo. METHODS: Rabbits (n = 73) instrumented for hemodynamic measurement and subjected to a 30-min left anterior descending coronary artery occlusion and 3-h reperfusion received 0.9% saline (control), isoflurane (0.5 or 1.0 minimum alveolar concentration [MAC]) administered for 3 min before and 2 min after reperfusion, the p53 inhibitor pifithrin-alpha (1.5 or 3.0 mg/kg), or 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha. Other rabbits received 3.0 mg/kg pifithrin-alpha or 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha after pretreatment with the selective PI3K inhibitor wortmannin (0.6 mg/kg) or the mitochondrial permeability transition pore opener atractyloside (5 mg/kg). RESULTS: Isoflurane (1.0 but not 0.5 MAC), pifithrin-alpha (3.0 but not 1.5 mg/kg), and the combination of 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha significantly (P < 0.05) reduced infarct size (21% +/- 4%, 43% +/- 7%, 22% +/- 4%, 45% +/- 4%, and 28% +/- 3% [mean +/- sd], respectively, of left ventricular area at risk; triphenyltetrazolium chloride staining) when compared with control (45% +/- 2%). Atractyloside, but not wortmannin, abolished 3.0 mg/kg pifithrin-alpha-induced cardioprotection, whereas atractyloside and wortmannin blocked reductions in infarct size produced by 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha. CONCLUSION: The results indicate that inhibition of the apoptotic protein p53 lowers the threshold of isoflurane-induced cardioprotection during early reperfusion in vivo.

Animals↗
PubMed2005

Axial stent strut angle influences wall shear stress after stent implantation: analysis using 3D computational fluid dynamics models of stent foreshortening.

INTRODUCTION: The success of vascular stents in the restoration of blood flow is limited by restenosis. Recent data generated from computational fluid dynamics (CFD) models suggest that the vascular geometry created by an implanted stent causes local alterations in wall shear stress (WSS) that are associated with neointimal hyperplasia (NH). Foreshortening is a potential limitation of stent design that may affect stent performance and the rate of restenosis. The angle created between axially aligned stent struts and the principal direction of blood flow varies with the degree to which the stent foreshortens after implantation. METHODS: In the current investigation, we tested the hypothesis that stent foreshortening adversely influences the distribution of WSS and WSS gradients using time-dependent 3D CFD simulations of normal arteries based on canine coronary artery measurements of diameter and blood flow. WSS and WSS gradients were calculated using conventional techniques in ideal (16 mm) and progressively foreshortened (14 and 12 mm) stented computational vessels. RESULTS: Stent foreshortening increased the intrastrut area of the luminal surface exposed to low WSS and elevated spatial WSS gradients. Progressive degrees of stent foreshortening were also associated with strut misalignment relative to the direction of blood flow as indicated by analysis of near-wall velocity vectors. CONCLUSION: The current results suggest that foreshortening may predispose the stented vessel to a higher risk of neointimal hyperplasia.

Animals↗
PubMed2005

Vascular endothelial growth factor is required for coronary collateral growth in the rat.

BACKGROUND: The goal of this study was to determine whether the expression of vascular endothelial growth factor (VEGF) is critical for coronary collateral growth. Previous studies have provided an association between coronary collateral growth and VEGF, but none have allowed determination of a causal role. METHODS AND RESULTS: We measured coronary collateral growth in rats subjected to repetitive episodes of myocardial ischemia (RI; one 40-second occlusion every 20 minutes for 2 hours 40 minutes, followed by 5 hours 20 minutes of rest, with this 8-hour cycle repeated 3 times per day for 10 days). Collateral growth was measured from blood flow (radioactive microspheres), visualization of arterial-arterial anastomoses (x-ray micro-CT), and maintenance of function during complete coronary occlusion in 3 groups of animals: sham (received instrumentation but no RI), experimental (subjected to RI), and anti-vascular endothelial growth factor (RI+anti-VEGF 0.6 mg/100 g per day) to block the endogenous actions of VEGF. In the 3 groups, native collateral flow (measurement for RI or sham protocol) averaged 0.2 to 0.3 mL x min(-1) x g(-1) of tissue. In the sham group, collateral flow did not increase during the protocol. Collateral flow in the control RI group increased by approximately 6-fold to 1.63 mL x min(-1) x g(-1) tissue, but in the anti-VEGF group, collateral flow did not increase after the RI protocol (0.22 mL x min(-1) x g(-1)). In acute experiments, collateral flow was unchanged during vasodilation with dipyridamole, indicating the increases in collateral flow are due to collateral growth and not vasodilation. X-ray micro-CT analysis revealed a 3-fold increase (versus sham group) in the number of arterial-arterial anastomoses per heart after RI, which was prevented by treatment with anti-VEGF. The growth of the collateral circulation was functional in the RI group because complete coronary occlusion did not induce any untoward effects on hemodynamics or arrhythmias. In the sham or anti-VEGF groups, coronary occlusion at the end of the protocol induced many arrhythmias and deterioration of function. CONCLUSIONS: From these results, we conclude that the expression of VEGF is critical to the growth of coronary collaterals.

Animals↗
PubMed2005

Characterization of a novel PKA phosphorylation site, serine-2030, reveals no PKA hyperphosphorylation of the cardiac ryanodine receptor in canine heart failure.

Hyperphosphorylation of the cardiac Ca2+ release channel (ryanodine receptor, RyR2) by protein kinase A (PKA) at serine-2808 has been proposed to be a key mechanism responsible for cardiac dysfunction in heart failure (HF). However, the sites of PKA phosphorylation in RyR2 and their phosphorylation status in HF are not well defined. Here we used various approaches to investigate the phosphorylation of RyR2 by PKA. Mutating serine-2808, which was thought to be the only PKA phosphorylation site in RyR2, did not abolish the phosphorylation of RyR2 by PKA. Two-dimensional phosphopeptide mapping revealed two major PKA phosphopeptides, one of which corresponded to the known serine-2808 site. Another, novel, PKA phosphorylation site, serine 2030, was identified by Edman sequencing. Using phospho-specific antibodies, we showed that the novel serine-2030 site was phosphorylated in rat cardiac myocytes stimulated with isoproterenol, but not in unstimulated cells, whereas serine-2808 was considerably phosphorylated before and after isoproterenol treatment. We further showed that serine-2030 was stoichiometrically phosphorylated by PKA, but not by CaMKII, and that mutations of serine-2030 altered neither the FKBP12.6-RyR2 interaction nor the Ca2+ dependence of [3H]ryanodine binding. Moreover, the levels of phosphorylation of RyR2 at serine-2030 and serine-2808 in both failing and non-failing canine hearts were similar. Together, our data indicate that serine-2030 is a major PKA phosphorylation site in RyR2 responding to acute beta-adrenergic stimulation, and that RyR2 is not hyperphosphorylated by PKA in canine HF.

Animals↗
PubMed2005

Alterations in wall shear stress predict sites of neointimal hyperplasia after stent implantation in rabbit iliac arteries.

Restenosis resulting from neointimal hyperplasia (NH) limits the effectiveness of intravascular stents. Rates of restenosis vary with stent geometry, but whether stents affect spatial and temporal distributions of wall shear stress (WSS) in vivo is unknown. We tested the hypothesis that alterations in spatial WSS after stent implantation predict sites of NH in rabbit iliac arteries. Antegrade iliac artery stent implantation was performed under angiography, and blood flow was measured before casting 14 or 21 days after implantation. Iliac artery blood flow domains were obtained from three-dimensional microfocal X-ray computed tomography imaging and reconstruction of the arterial casts. Indexes of WSS were determined using three-dimensional computational fluid dynamics. Vascular histology was unchanged proximal and distal to the stent. Time-dependent NH was localized within the stented region and was greatest in regions exposed to low WSS and acute elevations in spatial WSS gradients. The lowest values of WSS spatially localized to the stented area of a theoretical artery progressively increased after 14 and 21 days as NH occurred within these regions. This NH abolished spatial disparity in distributions of WSS. The results suggest that stents may introduce spatial alterations in WSS that modulate NH in vivo.

Animals↗
PubMed2005

Microfocal X-ray computed tomography post-processing operations for optimizing reconstruction volumes of stented arteries during 3D computational fluid dynamics modeling.

Restenosis caused by neointimal hyperplasia (NH) remains an important clinical problem after stent implantation. Restenosis varies with stent geometry, and idealized computational fluid dynamics (CFD) models have indicated that geometric properties of the implanted stent may differentially influence NH. However, 3D studies capturing the in vivo flow domain within stented vessels have not been conducted at a resolution sufficient to detect subtle alterations in vascular geometry caused by the stent and the subsequent temporal development of NH. We present the details and limitations of a series of post-processing operations used in conjunction with microfocal X-ray CT imaging and reconstruction to generate geometrically accurate flow domains within the localized region of a stent several weeks after implantation. Microfocal X-ray CT reconstruction volumes were subjected to an automated program to perform arterial thresholding, spatial orientation, and surface smoothing of stented and unstented rabbit iliac arteries several weeks after antegrade implantation. A transfer function was obtained for the current post-processing methodology containing reconstructed 16 mm stents implanted into rabbit iliac arteries for up to 21 days after implantation and resolved at circumferential and axial resolutions of 32 and 50 microm, respectively. The results indicate that the techniques presented are sufficient to resolve distributions of WSS with 80% accuracy in segments containing 16 surface perturbations over a 16 mm stented region. These methods will be used to test the hypothesis that reductions in normalized wall shear stress (WSS) and increases in the spatial disparity of WSS immediately after stent implantation may spatially correlate with the temporal development of NH within the stented region.

Angiography↗
PubMed2005

Isoflurane protects against myocardial infarction during early reperfusion by activation of phosphatidylinositol-3-kinase signal transduction: evidence for anesthetic-induced postconditioning in rabbits.

BACKGROUND: Brief episodes of ischemia during early reperfusion after coronary occlusion reduce the extent of myocardial infarction. Phosphatidylinositol-3-kinase (PI3K) signaling has been implicated in this "postconditioning" phenomenon. The authors tested the hypothesis that isoflurane produces cardioprotection during early reperfusion after myocardial ischemia by a PI3K-dependent mechanism. METHODS: Pentobarbital-anesthetized rabbits (n = 80) subjected to a 30-min coronary occlusion followed by 3 h reperfusion were assigned to receive saline (control), three cycles of postconditioning ischemia (10 or 20 s each), isoflurane (0.5 or 1.0 minimum alveolar concentration), or the PI3K inhibitor wortmannin (0.6 mg/kg, intravenously) or its vehicle dimethyl sulfoxide. Additional groups of rabbits were exposed to combined postconditioning ischemia (10 s) and 0.5 minimum alveolar concentration isoflurane in the presence and absence of wortmannin. Phosphorylation of Akt, a downstream target of PI3K, was assessed by Western blotting. RESULTS: Postconditioning ischemia for 20 s, but not 10 s, reduced infarct size (P < 0.05) (triphenyltetrazolium staining; 20 +/- 3% and 34 +/- 3% of the left ventricular area at risk, respectively) as compared with control (41 +/- 2%). Exposure to 1.0, but not 0.5, minimum alveolar concentration isoflurane decreased infarct size (21 +/- 2% and 43 +/- 3%, respectively). Wortmannin abolished the protective effects of postconditioning (20 s) and 1.0 minimum alveolar concentration isoflurane. Combined postconditioning (10 s) and 0.5 minimum alveolar concentration isoflurane markedly reduced infarct size (17 +/- 5%). This action was also abolished by wortmannin (44 +/- 2%). Isoflurane (1.0 minimum alveolar concentration) increased Akt phosphorylation after ischemia (32 +/- 6%), and this action was blocked by wortmannin. CONCLUSIONS: Isoflurane acts during early reperfusion after prolonged ischemia to salvage myocardium from infarction and reduces the threshold of ischemic postconditioning by activating PI3K.

Anesthetics, Inhalation↗