Class effects of SGLT2 inhibitors in mouse cardiomyocytes and hearts: inhibition of Na+/H+ exchanger, lowering of cytosolic Na+ and vasodilation.

AIMS/HYPOTHESIS: Sodium-glucose cotransporter 2 (SGLT2) inhibitors (SGLT2i) constitute a novel class of glucose-lowering (type 2) kidney-targeted agents. We recently reported that the SGLT2i empagliflozin (EMPA) reduced cardiac cytosolic Na+ ([Na+]c) and cytosolic Ca2+ ([Ca2+]c) concentrations through inhibition of Na+/H+ exchanger (NHE). Here, we examine (1) whether the SGLT2i dapagliflozin (DAPA) and canagliflozin (CANA) also inhibit NHE and reduce [Na+]c; (2) a structural model for the interaction of SGLT2i to NHE; (3) to what extent SGLT2i affect the haemodynamic and metabolic performance of isolated hearts of healthy mice. METHODS: Cardiac NHE activity and [Na+]c in mouse cardiomyocytes were measured in the presence of clinically relevant concentrations of EMPA (1 µmol/l), DAPA (1 µmol/l), CANA (3 µmol/l) or vehicle. NHE docking simulation studies were applied to explore potential binding sites for SGTL2i. Constant-flow Langendorff-perfused mouse hearts were subjected to SGLT2i for 30 min, and cardiovascular function, O2 consumption and energetics (phosphocreatine (PCr)/ATP) were determined. RESULTS: EMPA, DAPA and CANA inhibited NHE activity (measured through low pH recovery after NH4+ pulse: EMPA 6.69 ± 0.09, DAPA 6.77 ± 0.12 and CANA 6.80 ± 0.18 vs vehicle 7.09 ± 0.09; p < 0.001 for all three comparisons) and reduced [Na+]c (in mmol/l: EMPA 10.0 ± 0.5, DAPA 10.7 ± 0.7 and CANA 11.0 ± 0.9 vs vehicle 12.7 ± 0.7; p < 0.001). Docking studies provided high binding affinity of all three SGLT2i with the extracellular Na+-binding site of NHE. EMPA and CANA, but not DAPA, induced coronary vasodilation of the intact heart. PCr/ATP remained unaffected. CONCLUSIONS/INTERPRETATION: EMPA, DAPA and CANA directly inhibit cardiac NHE flux and reduce [Na+]c, possibly by binding with the Na+-binding site of NHE-1. Furthermore, EMPA and CANA affect the healthy heart by inducing vasodilation. The [Na+]c-lowering class effect of SGLT2i is a potential approach to combat elevated [Na+]c that is known to occur in heart failure and diabetes.

Cyclophilin D ablation is associated with increased end-ischemic mitochondrial hexokinase activity.

Both the absence of cyclophilin D (CypD) and the presence of mitochondrial bound hexokinase II (mtHKII) protect the heart against ischemia/reperfusion (I/R) injury. It is unknown whether CypD determines the amount of mtHKII in the heart. We examined whether CypD affects mtHK in normoxic, ischemic and preconditioned isolated mouse hearts. Wild type (WT) and CypD-/- mouse hearts were perfused with glucose only and subjected to 25 min ischemia and reperfusion. At baseline, cytosolic and mtHK was similar between hearts. CypD ablation protected against I/R injury and increased ischemic preconditioning (IPC) effects, without affecting end-ischemic mtHK. When hearts were perfused with glucose, glutamine, pyruvate and lactate, the preparation was more stable and CypD ablation-resulted in more protection that was associated with increased mtHK activity, leaving little room for additional protection by IPC. In conclusion, in glucose only-perfused hearts, deletion of CypD is not associated with end-ischemic mitochondrial-HK binding. In contrast, in the physiologically more relevant multiple-substrate perfusion model, deletion of CypD is associated with an increased mtHK activity, possibly explaining the increased protection against I/R injury.

In vivo mouse myocardial (31)P MRS using three-dimensional image-selected in vivo spectroscopy (3D ISIS): technical considerations and biochemical validations.

(31)P MRS provides a unique non-invasive window into myocardial energy homeostasis. Mouse models of cardiac disease are widely used in preclinical studies, but the application of (31)P MRS in the in vivo mouse heart has been limited. The small-sized, fast-beating mouse heart imposes challenges regarding localized signal acquisition devoid of contamination with signal originating from surrounding tissues. Here, we report the implementation and validation of three-dimensional image-selected in vivo spectroscopy (3D ISIS) for localized (31)P MRS of the in vivo mouse heart at 9.4 T. Cardiac (31)P MR spectra were acquired in vivo in healthy mice (n = 9) and in transverse aortic constricted (TAC) mice (n = 8) using respiratory-gated, cardiac-triggered 3D ISIS. Localization and potential signal contamination were assessed with (31)P MRS experiments in the anterior myocardial wall, liver, skeletal muscle and blood. For healthy hearts, results were validated against ex vivo biochemical assays. Effects of isoflurane anesthesia were assessed by measuring in vivo hemodynamics and blood gases. The myocardial energy status, assessed via the phosphocreatine (PCr) to adenosine 5'-triphosphate (ATP) ratio, was approximately 25% lower in TAC mice compared with controls (0.76 ± 0.13 versus 1.00 ± 0.15; P < 0.01). Localization with one-dimensional (1D) ISIS resulted in two-fold higher PCr/ATP ratios than measured with 3D ISIS, because of the high PCr levels of chest skeletal muscle that contaminate the 1D ISIS measurements. Ex vivo determinations of the myocardial PCr/ATP ratio (0.94 ± 0.24; n = 8) confirmed the in vivo observations in control mice. Heart rate (497 ± 76 beats/min), mean arterial pressure (90 ± 3.3 mmHg) and blood oxygen saturation (96.2 ± 0.6%) during the experimental conditions of in vivo (31)P MRS were within the normal physiological range. Our results show that respiratory-gated, cardiac-triggered 3D ISIS allows for non-invasive assessments of in vivo mouse myocardial energy homeostasis with (31)P MRS under physiological conditions.

Cardioprotective efficacy depends critically on pharmacological dose, duration of ischaemia, health status of animals and choice of anaesthetic regimen: a case study with folic acid.

BACKGROUND: Acute, high-dose folic acid (FA) administration has recently been shown to possess unprecedented effective cardioprotection against ischaemia/reperfusion (I/R) injury. Here we explore the translation potential of FA as treatment modality for cardiac I/R. METHODS: Dependency of FA protection on dose, ischaemia duration, and eNOS was examined in an isolated mouse heart I/R model, whereas dependency on animal health status and anaesthesia was examined in an in vivo rat model of regional cardiac I/R. RESULTS: 50 µM FA provided maximal reduction (by 95%) of I/R-induced cell death following 25 min ischaemia in isolated wild-type hearts, with protection associated with increased coupled eNOS protein. No protection was observed with 35 min I or in eNOS(-/-) hearts. Acute intravenous administration of FA during a 25 min ischaemic period reduced infarct size by 45% in in vivo pentobarbital-anaesthetised young, healthy rats. FA did not reduce infarct size in aged or pre-diabetic rats, although it did preserve hemodynamics in the pre-diabetic rats. Finally, using a clinically-relevant anaesthetic regimen of fentanyl-propofol anaesthesia, FA treatment was ineffective in young, aged and pre-diabetic animals. CONCLUSIONS: The protective potential of an initially promising cardioprotective treatment of high dose FA against cardiac I/R infarction, is critically dependent on experimental conditions with relevance to the clinical condition. Our data indicates the necessity of expanded pre-clinical testing of cardioprotective interventions before embarking on clinical testing, in order to prevent too many "lost-in-translation" drugs and unnecessary clinical studies.

Optimizing anesthetic regimen for surgery in mice through minimization of hemodynamic, metabolic, and inflammatory perturbations.

The role of anesthetics in animal research models is crucial, yet often ignored, and is almost never the primary focus of examination. Here, we investigated the impact of anesthetic regimens on different parameters of hemodynamics (blood pressure (BP) and heart rate (HR)), metabolism (glucose, insulin, and free fatty acids (FFA)), and inflammation (IL-6 and TNF-α) in two frequently used mouse strains (C57BL/6 and FVB). All animals were at a similar surgical plane of anesthesia, mechanically ventilated, and monitored for 60 min. The following anesthetic regimens were studied: (1) fentanyl-ketamine-midazolam (FKM), (2) fentanyl-midazolam-haldol (FMH), (3) pentobarbital (P), (4) fentanyl-fluanisone-midazolam (FFM), (5) fentanyl-midazolam-acepromazine (FMA), (6) ketamine-medetomidine-atropine (KMA), (7) isoflurane (ISO), and (8) propofol-fentanyl-midazolam (PFM). Metabolic and inflammatory parameters were compared with those obtained from non-anesthetized animals. Hemodynamics: BP >80 mm Hg were only obtained with KMA, whereas hypotension (BP <60 mm Hg) was observed with FKM and P. HR >500 beats/min was observed with ISO and PFM, whereas HR <400 beats/min was induced with KMA, FMH (BL/6), P (BL/6), and FKM (FVB). Metabolism: Glucose and insulin were most disturbed by KMA and ISO and mildly disturbed by FMA, whereas FFM, PFM, and P did not have any effect. FFA increased largely by FMA, with ISO and FKM having no effects. Inflammation: Cytokines were increased least with ISO/FFM/FMA, whereas FKM and KMA induced the largest increases in cytokines. When aiming at achieving surgical anesthesia without large disturbances in hemodynamic, metabolic, and inflammatory profiles, FFM, ISO, or PFM may be the most neutral anesthetic regimens in mice.

Pathophysiological consequences of TAT-HKII peptide administration are independent of impaired vascular function and ensuing ischemia.

RATIONALE: We have shown that partial dissociation of hexokinase II (HKII) from mitochondria in the intact heart using low-dose transactivating transcriptional factor (TAT)-HKII (200 nmol/L) prevents the cardioprotective effects of ischemic preconditioning, whereas high-dose TAT-HKII (10 µmol/L) administration results in rapid myocardial dysfunction, mitochondrial depolarization, and disintegration. In this issue of Circulation Research, Pasdois et al argue that the deleterious effects of TAT-HKII administration on cardiac function are likely because of vasoconstriction and ensuing ischemia. OBJECTIVE: To investigate whether altered vascular function and ensuing ischemia recapitulate the deleterious effects of TAT-HKII in intact myocardium. METHODS AND RESULTS: Using a variety of complementary techniques, including mitochondrial membrane potential (ΔΨm) imaging, high-resolution optical action potential mapping, analysis of lactate production, nicotinamide adenine dinucleotide epifluorescence, lactate dehydrogenase release, and electron microscopy, we provide direct evidence that refutes the notion that acute myocardial dysfunction by high-dose TAT-HKII peptide administration is a consequence of impaired vascular function. Moreover, we demonstrate that low-dose TAT-HKII treatment, which abrogates the protective effects of ischemic preconditioning, is not associated with ischemia or ischemic injury. CONCLUSIONS: Our findings challenge the notion that the effects of TAT-HKII are attributable to impaired vascular function and ensuing ischemia, thereby lending further credence to the role of mitochondria-bound HKII as a critical regulator of cardiac function, ischemia-reperfusion injury, and cardioprotection by ischemic preconditioning.

Deletion of the innate immune NLRP3 receptor abolishes cardiac ischemic preconditioning and is associated with decreased Il-6/STAT3 signaling.

OBJECTIVE: Recent studies indicate that the innate immune system is not only triggered by exogenous pathogens and pollutants, but also by endogenous danger signals released during ischemia and necrosis. As triggers for the innate immune NLRP3 inflammasome protein complex appear to overlap with those for cardiac ischemia-reperfusion (I/R) and ischemic preconditioning (IPC), we explored the possibility that the NLRP3 inflammasome is involved in IPC and acute I/R injury of the heart. PRINCIPAL FINDINGS: Baseline cardiac performance and acute I/R injury were investigated in isolated, Langendorff-perfused hearts from wild-type (WT), ASC(-/-) and NLRP3(-/-) mice. Deletion of NLRP3 inflammasome components ASC(-/-) or NLRP3(-/-) did not affect baseline performance. The deletions exacerbated I/R-induced mechanical dysfunction, but were without effect on I/R-induced cell death. When subjected to IPC, WT and ASC(-/-) hearts were protected against I/R injury (improved function and less cell death). However, IPC did not protect NLRP3(-/-) hearts against I/R injury. NLRP3(-/-) hearts had significantly decreased cardiac IL-6 levels with a trend towards lower IL-1ß levels at end reperfusion, suggesting abrogation of IPC through diminished IL-6 and/or IL-1ß signaling. Subsequent experiments showed that neutralising IL-6 using an antibody against IL-6 abrogated IPC in WT hearts. However, inhibition of the IL-1r receptor with the IL-1 receptor inhibitor Anakinra (100 mg/L) did not abrogate IPC in WT hearts. Analysis of survival kinases after IPC demonstrated decreased STAT3 expression in NLRP3(-/-) hearts when compared to WT hearts. CONCLUSIONS: The data suggest that the innate immune NLRP3 protein, in an NLRP3-inflammasome-independent fashion, is an integral component of IPC in the isolated heart, possibly through an IL-6/STAT3 dependent mechanism.

Reduced hexokinase II impairs muscle function 2 wk after ischemia-reperfusion through increased cell necrosis and fibrosis.

We previously demonstrated that hexokinase (HK) II plays a key role in the pathophysiology of ischemia-reperfusion (I/R) injury of the heart (Smeele et al. Circ Res 108: 1165-1169, 2011; Wu et al. Circ Res 108: 60-69, 2011). However, it is unknown whether HKII also plays a key role in I/R injury and healing thereafter in skeletal muscle, and if so, through which mechanisms. We used male wild-type (WT) and heterozygous HKII knockout mice (HKII(+/-)) and performed in vivo unilateral skeletal muscle I/R, executed by 90 min hindlimb occlusion using orthodontic rubber bands followed by 1 h, 1 day, or 14 days reperfusion. The contralateral (CON) limb was used as internal control. No difference was observed in muscle glycogen turnover between genotypes at 1 h reperfusion. At 1 day reperfusion, the model resulted in 36% initial cell necrosis in WT gastrocnemius medialis (GM) muscle that was doubled (76% cell necrosis) in the HKII(+/-) mice. I/R-induced apoptosis (29%) was similar between genotypes. HKII reduction eliminated I/R-induced mitochondrial Bax translocation and oxidative stress at 1 day reperfusion. At 14 days recovery, the tetanic force deficit of the reperfused GM (relative to control GM) was 35% for WT, which was doubled (70%) in HKII(+/-) mice, mirroring the initial damage observed for these muscles. I/R increased muscle fatigue resistance equally in GM of both genotypes. The number of regenerating fibers in WT muscle (17%) was also approximately doubled in HKII(+/-) I/R muscle (44%), thus again mirroring the increased cell death in HKII(+/-) mice at day 1 and suggesting that HKII does not significantly affect muscle regeneration capacity. Reduced HKII was also associated with doubling of I/R-induced fibrosis. In conclusion, reduced muscle HKII protein content results in impaired muscle functionality during recovery from I/R. The impaired recovery seems to be mainly a result of a greater susceptibility of HKII(+/-) mice to the initial I/R-induced necrosis (not apoptosis), and not a HKII-related deficiency in muscle regeneration.

Blood pressure influences end-stage renal disease of Cd151 knockout mice.

Podocytes of the kidney adhere tightly to the underlying glomerular basement membrane (GBM) in order to maintain a functional filtration barrier. The clinical importance of podocyte binding to the GBM via an integrin-laminin-actin axis has been illustrated in models with altered function of α3ß1 integrin, integrin-linked kinase, laminin-521, and α-actinin 4. Here we expanded on the podocyte-GBM binding model by showing that the main podocyte adhesion receptor, integrin α3ß1, interacts with the tetraspanin CD151 in situ in humans. Deletion of Cd151 in mouse glomerular epithelial cells led to reduced adhesive strength to laminin by redistributing α3ß1 at the cell-matrix interface. Moreover, in vivo podocyte-specific deletion of Cd151 led to glomerular nephropathy. Although global Cd151-null B6 mice were not susceptible to renal disease, as has been shown previously, increasing blood and transcapillary filtration pressure induced nephropathy in these mice. Importantly, blocking the angiotensin-converting enzyme in renal disease-susceptible global Cd151-null FVB mice prolonged their median life span. Together, these results establish CD151 as a crucial modifier of integrin-mediated adhesion of podocytes to the GBM and show that blood pressure is an important factor in the initiation and progression of Cd151 knockout-induced nephropathy.

The effect of standard chow and reduced hexokinase II on growth, cardiac and skeletal muscle hexokinase and low-flow cardiac ischaemia-reperfusion injury.

In the present study, we examined whether standard chow (SDS versus Purina 5001; both low fat, high carbohydrate) and reductions in hexokinase (HK) II (wild-type versus HKII(+/-) mice) affect (1) growth parameters, (2) HK levels in cardiac and skeletal muscle and (3) low-flow cardiac ischaemia-reperfusion (IR) injury. Total HK activity and HKI and HKII expressions were determined, and low-flow IR injury was examined in isolated hearts subjected to 40 min 5% low-flow ischaemia and 120 min reperfusion. Standard chow, but not HKII reductions, significantly affected body weight, heart weight and cardiac hypertrophy. Both standard chow and reduced HKII diminished total cardiac and skeletal muscle HK activity. For the heart, the Purina chow-induced decrease in total HK activity was through decreases in HKI expression, whereas for skeletal muscle post-translational mechanisms are suggested. Both standard chow and reduced HKII demonstrated a non-significant trend for affecting cardiac IR damage. However, the low-flow ischaemia model was associated with mild sublethal injury only (∼1% cell death). In conclusion, standard chow affects body weight, heart weight and HK activity and HKI expression in the heart, without altering HKII expression. This implicates standard chow as an important factor in genomic, physiological research models and demonstrates that large differences in fat or carbohydrates in the diet are not necessary to affect growth. In a cardiac low-flow IR model, resulting in only mild injury, standard chow or reduced HKII does not significantly affect IR damage.

Disruption of hexokinase II-mitochondrial binding blocks ischemic preconditioning and causes rapid cardiac necrosis.

RATIONALE: Isoforms I and II of the glycolytic enzyme hexokinase (HKI and HKII) are known to associate with mitochondria. It is unknown whether mitochondria-bound hexokinase is mandatory for ischemic preconditioning and normal functioning of the intact, beating heart. OBJECTIVE: We hypothesized that reducing mitochondrial hexokinase would abrogate ischemic preconditioning and disrupt myocardial function. METHODS AND RESULTS: Ex vivo perfused HKII(+/-) hearts exhibited increased cell death after ischemia and reperfusion injury compared with wild-type hearts; however, ischemic preconditioning was unaffected. To investigate acute reductions in mitochondrial HKII levels, wild-type hearts were treated with a TAT control peptide or a TAT-HK peptide that contained the binding motif of HKII to mitochondria, thereby disrupting the mitochondrial HKII association. Mitochondrial hexokinase was determined by HKI and HKII immunogold labeling and electron microscopy analysis. Low-dose (200 nmol/L) TAT-HK treatment significantly decreased mitochondrial HKII levels without affecting baseline cardiac function but dramatically increased ischemia-reperfusion injury and prevented the protective effects of ischemic preconditioning. Treatment for 15 minutes with high-dose (10 µmol/L) TAT-HK resulted in acute mitochondrial depolarization, mitochondrial swelling, profound contractile impairment, and severe cardiac disintegration. The detrimental effects of TAT-HK treatment were mimicked by mitochondrial membrane depolarization after mild mitochondrial uncoupling that did not cause direct mitochondrial permeability transition opening. CONCLUSIONS: Acute low-dose dissociation of HKII from mitochondria in heart prevented ischemic preconditioning, whereas high-dose HKII dissociation caused cessation of cardiac contraction and tissue disruption, likely through an acute mitochondrial membrane depolarization mechanism. The results suggest that the association of HKII with mitochondria is essential for the protective effects of ischemic preconditioning and normal cardiac function through maintenance of mitochondrial potential.

Partial hexokinase II knockout results in acute ischemia-reperfusion damage in skeletal muscle of male, but not female, mice.

Cellular studies have demonstrated a protective role of mitochondrial hexokinase against oxidative insults. It is unknown whether HK protective effects translate to the in vivo condition. In the present study, we hypothesize that HK affects acute ischemia-reperfusion injury in skeletal muscle of the intact animal. Male and female heterozygote knockout HKII (HK(+/-)), heterozygote overexpressed HKII (HK(tg)), and their wild-type (WT) C57Bl/6 littermates mice were examined. In anesthetized animals, the left gastrocnemius medialis (GM) muscle was connected to a force transducer and continuously stimulated (1-Hz twitches) during 60 min ischemia and 90 min reperfusion. Cell survival (%LDH) was defined by the amount of cytosolic lactate dehydrogenase (LDH) activity still present in the reperfused GM relative to the contralateral (non-ischemic) GM. Mitochondrial HK activity was 72.6 +/- 7.5, 15.7 +/- 1.7, and 8.8 +/- 0.9 mU/mg protein in male mice, and 72.7 +/- 3.7, 11.2 +/- 1.4, and 5.9 +/- 1.1 mU/mg in female mice for HK(tg), WT, and HK(+/-), respectively. Tetanic force recovery amounted to 33 +/- 7% for male and 17 +/- 4% for female mice and was similar for HK(tg), WT, and HK(+/-). However, cell survival was decreased (p = 0.014) in male HK(+/-) (82 +/- 4%LDH) as compared with WT (98 +/- 5%LDH) and HK(tg) (97 +/- 4%LDH). No effects of HKII on cell survival was observed in female mice (92 +/- 2% LDH). In conclusion, in this mild model of acute in vivo ischemia-reperfusion injury, a partial knockout of HKII was associated with increased cell death in male mice. The data suggest for the first time that HKII mediates skeletal muscle ischemia-reperfusion injury in the intact male animal.

Ischemic preconditioning affects hexokinase activity and HKII in different subcellular compartments throughout cardiac ischemia-reperfusion.

The glycolytic enzyme hexokinase (HK) is suggested to play a role in ischemic preconditioning (IPC). In the present study we determined how ischemic preconditioning affects HK activity and HKI and HKII protein content at five different time points and three different subcellular fractions throughout cardiac ischemia-reperfusion. Isolated Langendorff-perfused rat hearts (10 groups of 7 hearts each) were subjected to 35 min ischemia and 30 min reperfusion (control groups); the IPC groups were pretreated with 3 times 5-min ischemia. IPC was without effect on microsomal HK activity, and only decreased cytosolic HK activity at 35 min ischemia, which was mimicked by decreased cytosolic HKII, but not HKI, protein content. In contrast, mitochondrial HK activity at baseline and during reperfusion was elevated by IPC, without changes during ischemia. No effect of IPC on mitochondrial HK I protein content was observed. However, mitochondrial HK II protein content during reperfusion was augmented by IPC, albeit not following the IPC stimulus. It is concluded that IPC results in decreased cytosolic HK activity during ischemia that could be explained by decreased HKII protein content. IPC increased mitochondrial HK activity before ischemia and during reperfusion that was only mimicked by increased HK II protein content during reperfusion. IPC was without effect on the phosphorylation status of HK before ischemia. We conclude that IPC is associated with 1) a biphasic response of increased mitochondrial HK activity before and after ischemia, 2) decreased cytosolic HK activity during ischemia, and 3) cellular redistribution of HKII but not HKI.

Anesthesia's effects on plasma glucose and insulin and cardiac hexokinase at similar hemodynamics and without major surgical stress in fed rats.

BACKGROUND: Recent evidence suggests that hexokinase mitochondria association attenuates cell death, and that plasma glucose and insulin concentrations can influence clinical outcome. In the present study, we examined how different anesthetics per se affect these variables of glucose metabolism, i.e., under similar hemodynamic conditions and in the absence of major surgical stress. METHODS: In fed rats, the effects of pentobarbital (PENTO), isoflurane (ISO), sevoflurane (SEVO), ketamine-medetomidine-atropine (KMA), and sufentanil-propofol-morphine (SPM) on the cardiac cellular localization of hexokinase (HK) and levels of plasma glucose and insulin were determined and compared with values obtained in nonanesthetized animals (control). The role of mitochondrial and sarcolemmal K(ATP)-channels and alpha2-adrenergic receptor in ISO-induced hyperglycemia was also evaluated. RESULTS: Mean arterial blood pressure was similar among the different anesthetic strategies. PENTO (5.3 +/- 0.2 mM) and SPM (5.1 +/- 0.2 mM) had no significant effect on plasma glucose when compared with control (5.6 +/- 0.1 mM). All other anesthetics induced hyperglycemia: 7.4 +/- 0.2 mM (SEVO), 9.9 +/- 0.3 mM (ISO), and 14.8 +/- 1.0 mM (KMA). Insulin concentrations were increased with PENTO (2.13 +/- 0.13 ng/mL) when compared with control (0.59 +/- 0.22 ng/mL), but were unaffected by the other anesthetics. Inhibition of the mitochondrial K(ATP) channel (5-hydroxydecanoate acid) or the alpha(2)-adrenergic receptor (yohimbine) did not prevent ISO-induced hyperglycemia. Only the nonspecific K(ATP) channel inhibitor glibenclamide was able to prevent hyperglycemia by ISO. Cytoslic HK relative to total HK increased in the following sequence: control (35.5% +/- 2.1%), SEVO (35.5% +/- 2.7%), ISO (36.6% +/- 1.7%), PENTO (41.2% +/- 2.0%; P = 0.082 versus control), SPM (43.0% +/- 1.8%; P = 0.039 versus control), and KMA (46.6 +/- 2.3%; P = 0.002 versus control). CONCLUSIONS: Volatile anesthetics and KMA induce hyperglycemia, which can be explained, at least partly, by impaired glucose-induced insulin release. The data indicate that the inhibition of insulin release by ISO is mediated by sarcolemmal K(ATP) channel activation. The use of PENTO and SPM is not associated with hyperglycemia. SPM and KMA reduce the antiapoptotic association of HK with mitochondria.

Short-term hyperglycemia increases endothelial glycocalyx permeability and acutely decreases lineal density of capillaries with flowing red blood cells.

Hyperglycemia is becoming recognized as an important risk factor for microvascular dysfunction. We hypothesized that short-term hyperglycemia, either on the scale of hours or weeks, alters the barrier function and the volume of the endothelial glycocalyx and decreases functional capillary density and deformability of the red blood cells (RBCs). All experiments were performed in anesthetized, mechanically ventilated, C57BL/6 mice that were either normoglycemic, acutely hyperglycemic (25 mM) for 60 min due to infusion of glucose, or hyperglycemic (25 mM) for 2-4 wk (db/db mice). The glycocalyx was probed using 40-kDa Texas red dextran, which is known to permeate the glycocalyx, and 70-kDa FITC dextran, which has impaired access to the glycocalyx in healthy animals. Clearance of the dye from the blood was measured. An orthogonal polarization spectral imaging technique was used to visualize the number of capillaries with flowing RBCs of the dorsal flexor muscle. The data indicate that short-term hyperglycemia causes a rapid decrease of the ability of the glycocalyx to exclude 70-kDa dextran. No change in the vascular permeation of 40-kDa dextran was observed. Glycocalyx volume was not affected by short-term hyperglycemia. In addition, 1 h of hyperglycemia resulted in a 38% decrease of the lineal density of capillaries with flowing RBCs. This decreased lineal density was not observed in the 2- to 4-wk hyperglycemia model. Short-term hyperglycemia was without any effect on the deformablity of the RBCs. The data indicate that the described increased vascular permeability with hyperglycemia can be ascribed to an increased permeability of the glycocalyx, identifying the glycocalyx as a potential early target of hyperglycemia.