Experimental assessment of a myocyte-based multiscale model of cardiac contractile dysfunction.

Cardiac contractile dysfunction (CD) is a multifactorial syndrome caused by different acute or progressive diseases which hamper assessing the role of the underlying mechanisms characterizing a defined pathological condition. Mathematical modeling can help to understand the processes involved in CD and analyze their relative impact in the overall response. The aim of this study was thus to use a myocyte-based multiscale model of the circulatory system to simulate the effects of halothane, a volatile anesthetic which at high doses elicits significant acute CD both in isolated myocytes and intact animals. Ventricular chambers built using a human myocyte model were incorporated into a whole circulatory system represented by resistances and capacitances. Halothane-induced decreased sarco(endo)plasmic reticulum Ca2+ (SERCA2a) reuptake pump, transient outward K+ (Ito), Na+-Ca2+ exchanger (INCX) and L-type Ca2+ channel (ICaL) currents, together with ryanodine receptor (RyR2) increased open probability (Po) and reduced myofilament Ca2+ sensitivity, reproduced equivalent decreased action potential duration at 90% repolarization and intracellular Ca2+ concentration at the myocyte level reported in the literature. In the whole circulatory system, model reduction in mean arterial pressure, cardiac output and regional wall thickening fraction was similar to experimental results in open-chest sheep subjected to acute halothane overdose. Effective model performance indicates that the model structure could be used to study other changes in myocyte targets eliciting CD.

ß-adrenergic effects on cardiac myofilaments and contraction in an integrated rabbit ventricular myocyte model.

A five-state model of myofilament contraction was integrated into a well-established rabbit ventricular myocyte model of ion channels, Ca(2+) transporters and kinase signaling to analyze the relative contribution of different phosphorylation targets to the overall mechanical response driven by ß-adrenergic stimulation (ß-AS). ß-AS effect on sarcoplasmic reticulum Ca(2+) handling, Ca(2+), K(+) and Cl(-) currents, and Na(+)/K(+)-ATPase properties was included based on experimental data. The inotropic effect on the myofilaments was represented as reduced myofilament Ca(2+) sensitivity (XBCa) and titin stiffness, and increased cross-bridge (XB) cycling rate (XBcy). Assuming independent roles of XBCa and XBcy, the model reproduced experimental ß-AS responses on action potentials and Ca(2+) transient amplitude and kinetics. It also replicated the behavior of force-Ca(2+), release-restretch, length-step, stiffness-frequency and force-velocity relationships, and increased force and shortening in isometric and isotonic twitch contractions. The ß-AS effect was then switched off from individual targets to analyze their relative impact on contractility. Preventing ß-AS effects on L-type Ca(2+) channels or phospholamban limited Ca(2+) transients and contractile responses in parallel, while blocking phospholemman and K(+) channel (IKs) effects enhanced Ca(2+) and inotropy. Removal of ß-AS effects from XBCa enhanced contractile force while decreasing peak Ca(2+) (due to greater Ca(2+) buffering), but had less effect on shortening. Conversely, preventing ß-AS effects on XBcy preserved Ca(2+) transient effects, but blunted inotropy (both isometric force and especially shortening). Removal of titin effects had little impact on contraction. Finally, exclusion of ß-AS from XBCa and XBcy while preserving effects on other targets resulted in preserved peak isometric force response (with slower kinetics) but nearly abolished enhanced shortening. ß-AS effects on XBCa and XBcy have greater impact on isometric and isotonic contraction, respectively.

Role of CaMKII in post acidosis arrhythmias: a simulation study using a human myocyte model.

Postacidotic arrhythmias have been associated to increased sarcoplasmic reticulum (SR) Ca(2+) load and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activation. However, the molecular mechanisms underlying these arrhythmias are still unclear. To better understand this process, acidosis produced by CO2 increase from 5% to 30%, resulting in intracellular pH (pHi) change from 7.15 to 6.7, was incorporated into a myocyte model of excitation-contraction coupling and contractility, including acidotic inhibition of L-type Ca(2+) channel (I(CaL)), Na(+)-Ca(2+) exchanger, Ca(2+) release through the SR ryanodine receptor (RyR2) (I(rel)), Ca(2+) reuptake by the SR Ca(2+) ATPase2a (I(up)), Na(+)-K(+) pump, K(+) efflux through the inward rectifier K(+) channel and the transient outward K(+) flow (I(to)) together with increased activity of the Na(+)-H(+) exchanger (I(NHE)). Simulated CaMKII regulation affecting I(rel), I(up), I(CaL), I(NHE) and I(to) was introduced in the model to partially compensate the acidosis outcome. Late Na(+) current increase by CaMKII was also incorporated. Using this scheme and assuming that diastolic Ca(2+) leak through the RyR2 was modulated by the resting state of this channel and the difference between SR and dyadic cleft [Ca(2+)], postacidotic delayed after depolarizations (DADs) were triggered upon returning to normal pHi after 6 min acidosis. The model showed that DADs depend on SR Ca(2+) load and on increased Ca(2+) leak through RyR2. This postacidotic arrhythmogenic pattern relies mainly on CaMKII effect on I(CaL) and I(up), since its individual elimination produced the highest DAD reduction. The model further revealed that during the return to normal pHi, DADs are fully determined by SR Ca(2+) load at the end of acidosis. Thereafter, DADs are maintained by SR Ca(2+) reloading by Ca(2+) influx through the reverse NCX mode during the time period in which [Na(+)]i is elevated.

Determinants of Ca2+ release restitution: Insights from genetically altered animals and mathematical modeling.

Each heartbeat is followed by a refractory period. Recovery from refractoriness is known as Ca2+ release restitution (CRR), and its alterations are potential triggers of Ca2+ arrhythmias. Although the control of CRR has been associated with SR Ca2+ load and RYR2 Ca2+ sensitivity, the relative role of some of the determinants of CRR remains largely undefined. An intriguing point, difficult to dissect and previously neglected, is the possible independent effect of SR Ca2+ content versus the velocity of SR Ca2+ refilling on CRR. To assess these interrogations, we used isolated myocytes with phospholamban (PLN) ablation (PLNKO), knock-in mice with pseudoconstitutive CaMKII phosphorylation of RYR2 S2814 (S2814D), S2814D crossed with PLNKO mice (SDKO), and a previously validated human cardiac myocyte model. Restitution of cytosolic Ca2+ (Fura-2 AM) and L-type calcium current (ICaL; patch-clamp) was evaluated with a two-pulse (S1/S2) protocol. CRR and ICaL restitution increased as a function of the (S2-S1) coupling interval, following an exponential curve. When SR Ca2+ load was increased by increasing extracellular [Ca2+] from 2.0 to 4.0 mM, CRR and ICaL restitution were enhanced, suggesting that ICaL restitution may contribute to the faster CRR observed at 4.0 mM [Ca2+]. In contrast, ICaL restitution did not differ among the different mouse models. For a given SR Ca2+ load, CRR was accelerated in S2814D myocytes versus WT, but not in PLNKO and SDKO myocytes versus WT and S2814D, respectively. The model mimics all experimental data. Moreover, when the PLN ablation-induced decrease in RYR2 expression was corrected, the model revealed that CRR was accelerated in PLNKO and SDKO versus WT and S2814D myocytes, consistent with the enhanced velocity of refilling, SR [Ca2+] recovery, and CRR. We speculate that refilling rate might enhance CRR independently of SR Ca2+ load.

Simulation of steady state and transient cardiac muscle response experiments with a Huxley-based contraction model.

A cardiac muscle model is presented with the purpose of representing a wide range of mechanical experiments at constant and transient Ca(2+) concentration. Modifications of a previous model were: weak and power attached crossbridge states, a troponin system involving three consecutive regulatory troponin-tropomyosin units acting together in Ca(2+) kinetics and detachment constants depending on crossbridge length. This model improved cooperativity (Hill coefficient close to 4) and the force-velocity relationship, and incorporated the representation of the four phases of muscle response to length and force steps, isotonic shortening and isosarcometric contractions, preserving previous satisfactory results. Moreover, experimentally reported effects, such as length dependence on Ca(2+) affinity, the decreased cooperativity at higher Ca(2+) concentrations, temperature effects on the stiffness-frequency relationship and the isometric internal shortening due to series elasticity, were obtained. In conclusion, the model is more comprehensive than a previous version because it is able to represent a wider variety of steady state experiments, the mechanical variables in twitches can be adequately related to intracellular Ca(2+), and all the simulations were performed with the same set of parameters.

Expression of the MDR-1 gene-encoded P-glycoprotein in cardiomyocytes of conscious sheep undergoing acute myocardial ischemia followed by reperfusion.

We have recently reported that in chronic myocardial ischemia, adult mammalian cardiomyocytes express P-glycoprotein (P-gp). We now investigate if P-gp is also expressed in acute regional ischemia followed by reperfusion. Adult conscious sheep underwent 12-min occlusion of the mid-left anterior descending artery (inflatable cuff). Successful ischemia-reperfusion was confirmed by monitoring percent systolic left ventricular anterior wall thickening (sonomicrometry) during the whole ischemic period and every 10 min over 2 hr following cuff deflation. At 3, 24, and 48 hr after reperfusion, P-gp expression was investigated by immunohistochemistry and Western blot and MDR-1 mRNA by RT-PCR. Cardiomyocytes in the occluded artery territory (but not those in remote areas) consistently expressed P-gp at their sarcolemma. Whereas at 3 and 24 hr P-gp was mainly observed in the T tubules, at 48 hr it predominated in intercalated discs and gap junctions. RT-PCR and Western blot revealed higher expression in ischemic than in control myocardium. We conclude that in adult sheep with acute myocardial ischemia, the MDR-1 gene-encoded P-gp is expressed at the sarcolemma of the cardiomyocytes from 3 hr up to at least 48 hr after reperfusion.

Ischemic preconditioning protection against stunning in conscious diabetic sheep: role of glucose, insulin, sarcolemmal and mitochondrial KATP channels.

INTRODUCTION: Sarcolemmal and mitochondrial ATP-sensitive potassium (KATP) channels have been postulated to participate in preconditioning protection against infarction and stunning. However, these structures appear to be altered in diabetes and thus, it would be possible that preconditioning does not develop in diabetic hearts. OBJECTIVE: The purpose of this study was to know whether early (EP) and late (LP) ischemic preconditioning against stunning develop in conscious diabetic (D) sheep and whether diabetes affects KATP channel function. METHODS: Male castrated sheep received alloxan monohydrate (1 g) and were ascribed to three experimental groups: control [DC, 12 min of ischemia (i) followed by 2 h of reperfusion (r)], early preconditioning (DEP, six 5 min i-5 min r periods were performed 45 min before the 12 min i) and late preconditioning (DLP, same as DEP except that the preconditioning stimulus was performed 24 h before the 12 min i). Regional mechanics during reperfusion was evaluated by wall thickening fraction (%WTH) and expressed as percentage of basal values (100%), and KATP channel behavior was indirectly assessed by monophasic action potential duration (MAPD) in relation to its sensitivity to glibenclamide blockade (0.1 and 0.4 mg/kg). The results were compared to those obtained in normal (N) sheep. The effects of sarcolemmal and mitochondrial KATP channel blockade on recovery from stunning were assessed by administration of glibenclamide (0.1 and 0.4 mg/kg) and 5-hydroxydecanoate (5-HD, 5 mg/kg i.v.) and/or diazoxide (10 microg/kg/min over 90 min). Whether acute hyperglycemia (H) in normal animals and insulin (I) treatment in diabetic sheep affected preconditioning protection and KATP channel behavior were also evaluated. RESULTS: Results expressed as mean % recovery of %WTH showed that preconditioning protected against stunning in normal sheep (NC=65+/-3.5, NLP=82+/-6**, NEP=76+/-4*, *P<0.05 and **P<0.01 against NC) while this did not occur in diabetic ones, where DLP (58+/-7.6) afforded a similar recovery to DC (54+/-5) and DEP worsened instead of improving mechanical function (37+/-9, P<0.01 against DC). Acute hyperglycemia did not affect preconditioning development (NEPH=72+/-3 and NLPH=80+/-4) and insulin treatment reverted the lack of early and late preconditioning protection in diabetic hearts (DEPI=72+/-4* and DLPI=76+/-3*, P<0.05 against DC). Sarcolemmal KATP channel behavior appeared altered in diabetic hearts as shown by MAPD in normal sheep (276+10 ms) compared to diabetic ones (365+9 ms, P<0.05) and by the sensitivity to glibenclamide [0.1 mg/kg completely blocked KATP channels in diabetic (P<0.05) but not in normal hearts]. Insulin also restored MAPD in diabetic heart. Mitochondrial KATP channels appeared not to account for the reported results in diabetes, since glibenclamide (%WTH=40+/-4, P<0.01 vs. NC), but not 5HD nor diazoxide affected myocardial functional recovery during reperfusion. CONCLUSIONS: Sarcolemmal KATP channel dysfunction due to the lack of insulin affords a primary approach to explain the absence of preconditioning protection against stunning in diabetic sheep hearts.

[Effect of different doses of aspirin on preconditioning against stunning in conscious sheep]. / Efecto de diferentes dosis de aspirina sobre el precondicionamiento contra el atontamiento en ovejas.

UNLABELLED: Non-steroid antiinflammatory drugs, inhibitors of cyclooxigenase (COX), have been postulated to have deletereous effects on the heart. Recently, COX-2 inhibitors have also been found to block late preconditioning (LP) protection. Aspirin is the most widely clinically used non-steroid antiinflammatory drug; yet its effect on LP in big mammals has not been determined. It inhibits the two cyclooxigenase isoenzymes (COX-1 and COX-2), at high doses being used as an antiinflammatory drug and at low doses as an antithrombotic agent. The goal of this study was thus, to analyse the effect of different aspirin doses on LP protection against stunning and arrhythmias in a conscious sheep model. The animals were divided in 5 groups: control (C): 12 min ischemia (I)-2 hr reperfusion (R); LP: 6 periods of 5 min I-5 min R, 24 hr before 12 min I, and three groups same as LP, but with 1.5 (LPA1.5), 8 (LPA8) and 20 (LPA20) mg/kg aspirin respectively, administered 10 min before the first preconditioning I. Results showed that the antiinflammatory dose of aspirin (20 mg/kg) was able to inhibit LP against stunning (C vs LPA20, NS), whereas low (1.5 mg/kg) and intermediate (8 mg/kg) doses did not interfere with the protection (C vs LP, LPA1.5 and LPA8, p < 0.01). Moreover, no dose altered the protection against arrhythmias. CONCLUSION: Antithrombotic aspirin doses would not inhibit LP protection against stunning, whereas high antiinflammatory doses would be potentially deletereous. Since high doses of aspirin blocked LP when administered before the triggering episodes, our results show that the COX pathway might be involved as a trigger of LP against stunning.

Cardiac output assessment using oxygen consumption estimated from the left ventricular pressure-volume area.

Use of a majority of structural variables (age, sex, height) to estimate oxygen consumption in the calculation of cardiac output (CO) by the Fick principle does not account for changes in physiological conditions. To improve this limitation, oxygen consumption was estimated based on the left ventricular pressure-volume area. A pilot study with 10 patients undergoing right cardiac catheterization showed that this approach was successful to estimate CO (r=0,73, vs. thermodilution measured CO). Further essays changing end-diastolic-volume in the pressure-volume area formula by body weight or body surface area showed that this last yielded the best correlation with the thermodilution measured CO (slope=1, ordinate =0.01 and r=0.93). These preliminary results indicate that use of a formula originated from the pressure-volume-area concept is a good alternative to estimate oxygen consumption for CO calculation.

La adventicia arterial: actor olvidado del sistema cardiovascular

Actualmente se acepta que la adventicia tiene: un importante rol fisiológico al determinar el nivel de nutrición, oxigenación, reparación arterial, regulación de la vasomotricidad, control de la poscarga ventricular, control de la función arterial, etcétera, a la vez que tiene una importante participación en procesos patológicos (por ejemplo, aterosclerosis, hipertensión arterial, génesis de aneurismas de aorta abdominal). Sin embargo, dado lo reciente de la mayoría de los estudios que han redefinido el rol de la adventicia, aún persiste mucho desconocimiento en la comunidad biomédica acerca de la fisiología de la capa adventicia arterial. El presente trabajo tiene como objetivo revisar el rol que actualmente se reconoce para la capa adventicia de la pared arterial.

Failure of IL-8 to assess early reperfusion injury following lung transplantation of cardiac death donor pigs.

Although interleukins (IL) 8 and 10 predict lung viability in lung transplantation from heart beating donors (HBD) and IL-1beta is a marker of ex vivo performance from after cardiac death donors (ACDD), IL expression in the recipient remains unknown. This study assessed IL-1beta, IL-8 and IL-10 as indicators of functional performance in single-lung transplantation from ACDD pigs. Animals were divided into: (i) HBD: immediate lung excision; (ii) ACDD: fibrillation, 30 min warm ischemia and 3 h topical cooling. Left lungs of both groups were then flushed with Perfadex and stored at 3-4 degrees C for 3 h. IL in bronchoalveolar lavage fluid (BAL) and hemodynamic and graft function were measured in the donor and during the 2 h reperfusion period in the recipient. Myeloperoxidase, nuclear factor kappa beta, wet/dry weight ratio and a histologic injury score were assessed from biopsies in basal conditions in the donor and at the end of reperfusion. Despite similar pulmonary function and histologic markers of injury in both groups and higher IL-1beta in the donor of ACDD, IL-8 during reperfusion was significantly lower in ACDD (119 +/- 33% of basal) than in HBD (306 +/- 238%, P < 0.05) recipients. The paradoxical behavior of IL-8 makes it an unreliable predictor of ACDD early outcome in this transplantation model.

Nitroglycerin induces late preconditioning against arrhythmias but not stunning in conscious sheep.

OBJECTIVES: Nitroglycerin, a nitric oxide donor, induces late preconditioning against stunning by short ischemia-reperfusion periods. The study purpose was to assess similar nitroglycerin protection against stunning and arrhythmias produced by prolonged reversible ischemia. DESIGN: Four groups of conscious sheep were studied, control: 12 minutes ischemia and 2 hour reperfusion; late preconditioning: six periods of 5 min ischemia-5 min reperfusion 24 h before 12 min ischemia and late preconditioning with 120 microg/kg and 600 microg/kg nitroglycerin administered instead of the ischemia-reperfusion periods. RESULTS: Although late preconditioning protected against stunning (mean postischemic recovery of wall thickening fraction, control (n=10): 54.8+/-3.2, late preconditioning (n=9): 74.4+/-3.0, p<0.01), nitroglycerin 120 microg/kg (n=6) did not reproduce mechanical protection (50.1+/-3.8), even with a higher concentration of 600 microg/kg (59.1+/-3.7, n=4). However, nitroglycerin decreased arrhythmia severity index (control: 2.3+/-0.6, late preconditioning: 0.5+/-0.4, nitroglycerin 120 microg/kg: 1+/-0.4 and 600 microg/kg: 0.1+/-0.1 (p<0.05 vs. control). CONCLUSIONS: Nitroglycerin only has a limited late preconditioning protective effect in conscious animals submitted to a reversible prolonged ischemia since it protects against arrhythmias but not against stunning.

Role of the cyclooxygenase pathway in the protection against postischemic stunning in conscious sheep.

OBJECTIVE: There are controversial reports in conscious animals regarding the role of cyclooxygenase-2 in late preconditioning (LP). This study analyzed the effect of COX-2 involvement in non-preconditioned hearts (NP) and in mediation of LP protection against stunning in conscious sheep submitted to a prolonged reversible ischemia. METHODS: Six groups were considered: NP: 12 min ischemia and 120 min reperfusion; LP consisting of six periods of 5 min-ischemia-5 min reperfusion 24 h before the 12 min ischemia; NP and LP with either the non-selective COX-1 and COX-2 inhibitor, aspirin (20 mg/kg), or the specific COX-2 inhibitor, celecoxib (3 mg/kg) before the 12 min ischemic period. RESULTS: Mean postischemic wall thickening fraction (as % of preischemic values) improved from 49.6 +/- 4.0% in NP to 72.5 +/- 3.5% in LP (p < 0.01) and a similar protection was obtained with aspirin and celecoxib in NP hearts (p < 0.01). Neither aspirin nor celecoxib administration prior to the prolonged ischemia on day 2 abrogated LP improvement of postischemic dysfunction. Moreover, LP with aspirin improved the protective response (80.7 +/- 2.6%) over that obtained with aspirin in NP hearts (66.6 +/- 4.7%, p < 0.05). This effect was not obtained with celecoxib. CONCLUSIONS: Aspirin and celecoxib showed that COX-2 has a detrimental effect on mechanical cardioprotection in NP hearts of conscious sheep submitted to a prolonged reversible ischemia, and does not seem to participate as mediator of LP. Aspirin revealed a similar COX-1 deleterious action, since only when both COX-1 and COX-2 were inhibited, LP was put in evidence adding functional improvement over that obtained in NP hearts treated with aspirin.

ATP-sensitive potassium channels do not have a main role in mediating late preconditioning protection against arrhythmias and stunning in conscious sheep.

OBJECTIVE: Although late preconditioning protects against stunning following several short periods of ischemia-reperfusion, it is not clear if it confers protection against stunning and malignant arrhythmias after a sustained reversible ischemia, and whether KATP channels are involved as triggers and/or end effectors of the protective mechanism. The purpose of this work was thus to test these issues in conscious sheep. METHODS: Five groups were considered: CONT (control): the animals were submitted to 12 min ischemia followed by 2 h reperfusion; SWOP (late preconditioning): on the first day, the animals were preconditioned with 6 periods of 5 min ischemia 5 min reperfusion and 24 h later they were submitted to 12 min ischemia followed by 2 h reperfusion; GLIB: same as CONT with the KATP channel inhibitor glibenclamide (0.4 mg/kg) infused 30 min prior to the 12 min ischemia; SWOPG2: same as SWOP with glibenclamide before the 12 min ischemia; SWOPG1: same as SWOP with glibenclamide prior to the preconditioning stimulus. RESULTS: Percent reperfusion recovery of wall thickening fraction (% WTh) showed late preconditioning protection against stunning throughout reperfusion (SWOP vs CONT, p < 0.01). Arrhythmia severity index (ASI) also demonstrated that late preconditioning protects against malignant arrhythmias at the onset of reperfusion (CONT: 4.87 +/- 1.62 vs SWOP: 1.39 +/- 0.93, p < 0.01). Glibenclamide was unable to prevent preconditioning, both against stunning and arrhythmia incidence, when administered either before the preconditioning stimulus (SWOPG1 vs CONT, p < 0.01) or before the sustained ischemia (SWOPG2 vs GLI, p < 0.01). CONCLUSIONS: Results indicate that late preconditioning protects against stunning and arrhythmias following a reversible, sustained ischemia in conscious sheep and that KATP channel participation is negligible as triggers and end effectors of both types of protection.

Absence of ischemic preconditioning protection in diabetic sheep hearts: role of sarcolemmal KATP channel dysfunction.

Sarcolemmal ATP-sensitive potassium (KATP) channels have been mentioned to participate in preconditioning protection. Since these channels are altered in diabetes, it would be possible that preconditioning does not develop in diabetic (D) hearts. The purpose of this study was to assess whether early (EP) and late (LP) ischemic preconditioning protect diabetic hearts against stunning in a conscious diabetic sheep model and whether diabetes might have altered KATP channel functioning. Sheep received alloxan monohydrate (1 g) and were ascribed to three experimental groups: control (DC, 12 min of ischemia (I) followed by 2 h of reperfusion (R)), early preconditioning (DEP, six 5 min I-5 min R periods were performed before the 12 min I) and late preconditioning (DLP, same as DEP except that the preconditioning stimulus was performed 24 h before the 12 min I). Regional mechanics during reperfusion was evaluated as the percent recovery of wall thickening fraction (%WTH) expressed as percentage of basal values (100%) and KATP behaviour was indirectly assessed by monophasic action potential duration (MAPD) and sensitivity to glibenclamide blockade (0.1 and 0.4 mg/Kg). The results were compared to those obtained in normal (N) sheep. EP and LP protected against stunning in normal sheep (%WTH: NC = 63 +/- 3.7, NLP = 80 +/- 5**, NEP = 78 +/- 3*, *p < 0.05 and **p < 0.01 against NC) whereas contrary results occurred in diabetic ones, where DLP (%WTH = 60 +/- 4) afforded a similar recovery to DC (%WTH = 54 +/- 5) and DEP surprisingly worsened instead of improving mechanical function (%WTH = 38 +/- 6, p < 0.01 against DC). KATP channel behaviour appeared altered in diabetic hearts as shown by MAPD during ischemia in normal sheep (153 +/- 9 msec) compared to diabetic ones (128 +/- 11 msec, p < 0.05) and by the sensitivity to glibenclamide (while 0.4 mg/Kg blocked action potential shortening in normal and diabetic animals, 0.1 mg/Kg completely blocked KATP in diabetic but not in normal hearts, p < 0.05). A sarcolemmal KATP channel dysfunction might afford a primary approach to explain the absence of ischemic preconditioning protection against stunning in diabetic sheep.

Ischemic shortening of action potential duration as a result of KATP channel opening attenuates myocardial stunning by reducing calcium influx.

Action potential duration (APD) shortening due to opening of sarcolemmal ATP-dependent potassium (KATP) channels has been postulated to protect the myocardium against postischemic damage by reducing Ca2+ influx. This hypothesis was assessed, assuming that increased postischemic stunning due to KATP channel inhibition with glibenclamide could be reverted by the addition of the Ca2+ channel blocker diltiazem. Percent wall thickening fraction (%WTh, conscious sheep) and APD (open-chest sheep) were obtained from the following groups: control: 12 min ischemia by anterior descending coronary artery occlusion followed by 2 h reperfusion; glibenclamide: same as control, with glibenclamide (0.4 mg/kg) infused 30 min before ischemia; diltiazem: same as control, with diltiazem (100 microg/kg) administered prior to ischemia; glibenclamide+diltiazem: both drugs infused as in glibenclamide and diltiazem groups. APD was reduced in control ischemia. Conversely, KATP-channel blockade by glibenclamide lengthened APD and increased postischemic stunning (p < 0.01 vs. control); glibenclamide+diltiazem did not shorten APD but enhanced functional recovery (p < 0.01 vs. glibenclamide). Ca2+ channel blockade improvement of increased stunning provoked by KATP channel inhibition supports the hypothesis that APD shortening due to opening of KATP channels protects against postischemic stunning by limiting Ca2+ influx.

Efecto de diferentes dosis de asoirina sobre el precondocionamiento contra el atontamiento en ovejas / Effect of different doses of aspirin on preconditioning against stunning in conscious sheep

Se ha postulado que los antiinflamatorios no esteroides que actuan inhibiendo la ciclooxigenasa (COX) podrían tener efectos nocivos sobre el corazón. Recientemente se ha demostrado que los inhibidores de la COX-2 bloquean la protección por precondicionamiento tardío (PT). Se desconoce sin embargo, el efecto que pudiera tener la aspirina, el antiinflamatorio no esteroide más ampliamente utilizado en la clínica, sobre el PT en mamíferos grandes. La aspirina actúa inhibiendo las dos isoenzimas de la ciclooxigenasa (COX-1 y COX-2), siendo empleada en dosis altas como droga antiinflamatoria y en dosis bajas como agente antitrombótico.El propósito de este estudio fue analizar qué efecto tienen distintas dosis de aspirina sobre la protección delPT contra el atontamiento y las arritmias en ovejas conscientes. Se consideraron 5 grupos; control (C): 12 minde isquemia (I) y 2 hr de reperfusión (R); PT: 6 períodos de 5 min I-5 min R, 24 hr antes de la I de 12 min, ytres grupos igual que PT, pero con 1.5 (PTA1.5), 8 (PTA8) y 20 (PTA20) mg/kg de aspirina respectivamente, administrados 10 min antes de la primera I de precondicionamiento. Los resultados demostraron que la dosis antiinflamatoria de aspirina (20 mg/kg) fue capaz de inhibir el PT contra el atontamiento (C vs PTA20, NS),mientras que las dosis bajas (1.5 mg/kg) e intermedia (8 mg/kg) no afectaron la protección (C vs PT, PT1.5 yPT8, p<0.01). Asimismo, ninguna de las tres dosis alteró la protección contra las arritmias. Conclusión: Lasdosis antiagregantes plaquetarias de aspirina no producirían riesgo de inhibir la protección contra el atontamiento por PT, mientras que dosis antiinflamatorias elevadas serían perjudiciales. Como la aspirina se administró antes de los períodos precondicionantes, la inhibición de la cardioprotección sugiere que la COX actúacomo mecanismo gatillador del PT contra el atontamiento.