Sakuji Shigematsu

Resveratrol, a red wine constituent polyphenol, prevents superoxide-dependent inflammatory responses induced by ischemia/reperfusion, platelet-activating factor, or oxidants.

Moderate consumption of red wine has been shown to exert cardioprotection against ischemia/reperfusion. Because oxidant-dependent leukocyte infiltration plays a critical role in ischemia/reperfusion-induced tissue injury, we hypothesized that resveratrol, a red wine constituent polyphenol would attenuate postischemic leukocyte recruitment and subsequent endothelial dysfunction. Intravital microscopic approaches were used to quantify leukocyte/endothelial cell interactions and venular protein leakage in rat mesenteries exposed to either 20 min ischemia and 60 min reperfusion (I/R), oxidants generated by the reaction of hypoxanthine and xanthine oxidase (HX/XO), platelet-activating factor (PAF), or leukotriene B4 (LTB4). I/R or HX/HX produced marked increases in the number of adherent (LA) and emigrated (LE) leukocytes, which were associated with significant increases in venular albumin leakage (VAL). Intravenous administration of resveratrol or superoxide dismutase (SOD) attenuated these increases in LA, LE, and VAL. Superfusion of the mesentery with PAF or LTB4 also markedly increased LA, LE, and VAL. While resveratrol attenuated the proinflammatory effects of PAF, LTB4-induced changes were not affected by resveratrol. Resveratrol prevents leukocyte recruitment and endothelial barrier disruption induced by a number of superoxide-dependent proinflammatory stimuli, including I/R, HX/XO, or PAF. These salutary effects appear to be related to the antioxidant properties of resveratrol and contribute to the cardioprotective actions associated with consumption of red wine.

Pharmacological Evidence for the Persistent Activation of ATP-Sensitive K+ Channels in Early Phase of Reperfusion and Its Protective Role Against Myocardial Stunning

BACKGROUND The activation of cardiac ATP-sensitive potassium channels is reported to protect myocardium during ischemia. However, the behavior and role of this channel during reperfusion remain uncertain. METHODS AND RESULTS Guinea pig right ventricular walls were studied by use of microelectrodes and a force transducer. Each preparation was perfused via the coronary artery at a constant flow rate and was stimulated at 3 Hz. In the first protocol, the preparation was subjected to 10 minutes of no-flow ischemia, which was followed by 60 minutes of reperfusion. Introduction of ischemia shortened the action potential duration (APD) to 58.7 +/- 3.1% of the preischemic values, in association with a decrease in the resting membrane potential (by 12 +/- 0.8 mV) and action potential amplitude (by 34.6 +/- 1.8 mV). On reperfusion, although the APD was restored, it remained shortened for up to approximately 30 minutes of reperfusion. In the presence of glibenclamide (10 mumol/L), the shortening of the APD during ischemia was significantly attenuated and the restoration of APD after reperfusion was significantly facilitated. When glibenclamide was applied from the onset of reperfusion, the persistent APD shortening was significantly suppressed. The developed tension decreased during ischemia and recovered after 60 minutes of reperfusion (up to 92.0 +/- 6.4% of preischemic values) in the untreated preparations. The application of glibenclamide that was started before ischemia or from the onset of reperfusion significantly suppressed the recovery of contractility (P < .05 versus untreated preparations). In the second series of experiments, 20 minutes of no-flow ischemia and 60 minutes of reperfusion were applied. This protocol produced a sustained contractile dysfunction after reperfusion (to 34.0 +/- 3.2% of preischemic values). In the presence of cromakalim (2 mumol/L), the APD shortening was enhanced during both ischemia and the early reperfusion period. Cromakalim significantly improved the contractile recovery (to 79.3 +/- 4.1% of preischemic values, P < .05 versus untreated preparations). The application of cromakalim that was started from the onset of reperfusion also improved the contractile recovery during this phase and this effect was associated with enhanced APD shortening. However, the cromakalim-treated preparations demonstrated a higher incidence of ventricular fibrillation during reperfusion. CONCLUSIONS Cardiac ATP-sensitive potassium channels are activated by ischemia, and a fraction of these channels remains activated during the early reperfusion phase. The resulting shortening of the APD prevents the heart from developing myocardial stunning.

Effect of essential hypertension on cardiac autonomic function in type 2 diabetic patients.

OBJECTIVES The aim of this study was to examine the effects of essential hypertension on cardiac autonomic function in type 2 diabetic patients. BACKGROUND Hypertension is common in type 2 diabetic patients and is associated with a high mortality. However, the combined effects of type 2 diabetes and essential hypertension on cardiac autonomic function have not been fully elucidated. METHODS Thirty-three patients with type 2 diabetes were assigned to a hypertensive diabetic group (n = 15; age: 56 +/- 8 years, mean +/- SD) or an age-matched normotensive diabetic group (n = 18, 56 +/- 6 years). Cardiac autonomic function was assessed by baroreflex sensitivity (BRS), heart rate variability (HRV), plasma norepinephrine concentration and cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphic findings. RESULTS Baroreflex sensitivity was lower in the hypertensive diabetic group than it was in the normotensive diabetic group (p < 0.05). The early and delayed myocardial uptake of 123I-MIBG was lower (p < 0.01 and p < 0.05, respectively), and the percent washout rate of 123I-MIBG was higher (p < 0.05) in the hypertensive diabetic group. However, the high frequency (HF) power and the ratio of low frequency (LF) power to HF power (LF/HF) of HRV and plasma norepinephrine concentration were not significantly different. The homeostasis model assessment index was higher in the hypertensive diabetic group than it was in the normotensive diabetic group (p < 0.01). CONCLUSIONS Our results indicate that essential hypertension acts synergistically with type 2 diabetes to depress cardiac reflex vagal and sympathetic function, and the results also suggest that insulin resistance may play a pathogenic role in these processes.

Phosphatidylinositol 3-kinase-dependent activation of akt, an essential signal for hyperthermia-induced heat-shock protein 72, is attenuated in streptozotocin-induced diabetic heart

We tested the hypothesis that phosphatidylinositol 3-kinase (PI 3-kinase)-dependent activation of Akt is essential for the expression of cardiac heat-shock protein 72 (HSP72) and that this pathway is impaired in the streptozotocin (STZ)-induced diabetic heart. STZ-induced male diabetic rats were treated with insulin (STZ-insulin group, n = 26) or vehicle (STZ-vehicle group, n = 61) for 3 weeks. Whole-body hyperthermia (43°C for 20 min) was applied, and the heart was isolated 24 h later. Compared with control heart, hyperthermia-induced HSP72 expression and phosphorylation of Akt were attenuated in the STZ-vehicle heart. Pretreatment with wortmannin attenuated hyperthermia-induced HSP72 expression and phosphorylation of Akt. In isolated perfused heart experiments, the hyperthermia-treated STZ-vehicle heart showed poor left ventricular functional recovery during reperfusion after no-flow global ischemia compared with hyperthermia-treated control heart. Insulin treatment restored HSP72 expression and reperfusion-induced functional recovery. In cultured neonatal rat cardiomyocytes, hyperthermia-induced HSP72 expression was enhanced by insulin, together with tolerance against hypoxia-reoxygenation injury. Wortmannin and LY294002 inhibited hyperthermia-induced HSP72 expression and phosphorylation of Akt. Our results indicate that activation of Akt, in a PI 3-kinase–dependent manner, is essential for hyperthermia-induced HSP72 expression in association with cardioprotection, suggesting impairment of this signaling pathway in the STZ-induced diabetic heart, probably due to insulin deficiency.

Anoxia-induced activation of ATP-sensitive K+ channels in guinea pig ventricular cells and its modulation by glycolysis

OBJECTIVE Exposure to anoxia has been reported to activate ATP-sensitive potassium (K+(ATP)) channels in isolated ventricular myocytes. We aimed to investigate the mechanisms underlying the anoxia-induced activation of K+(ATP) channels. METHODS Guinea pig ventricular myocytes were isolated using collagenase digestion. Action potentials and membrane currents were recorded in the whole-cell mode of patch clamp. Exposure to anoxia was performed in a semi-closed airtight chamber, which prevented the diffusion of atmospheric oxygen into anoxic perfusate. RESULTS Exposure to glucose-free anoxia shortened the action potential duration (APD) to less than 20% of control in 13 +/- 3 min. Subsequent reoxygenation rapidly and completely restored the APD. The time-independent large outward current which developed during anoxia was completely suppressed by reoxygenation or by the application of glibenclamide, a K+(ATP) channel blocker. The presence of extracellular glucose did not prevent APD shortening during anoxia, although it significantly decreased the rate of shortening. Reoxygenation-induced restoration of the APD was inhibited after a long-lasting anoxia. In addition, repeated exposures to anoxia/reoxygenation progressively impaired the recovery of APD during reoxygenation. CONCLUSIONS Activation of K+(ATP) channels occurs during anoxia. The primary source of ATP that regulates the channel activity seems to be oxidative phosphorylation. ATP derived from anaerobic glycolysis (attained by the increase of extracellular glucose) was observed to partially suppress the channel activity only when oxidative phosphorylation was severely impaired during anoxia.

JTV-519, a novel cardioprotective agent, improves the contractile recovery after ischaemia-reperfusion in coronary perfused guinea-pig ventricular muscles

A newly synthesized benzothiazepine derivative, JTV‐519 (JT) has been reported to be cardioprotective. However, the precise mechanism underlying the cardioprotective effect of this drug is unknown. Coronary‐perfused guinea‐pig ventricular muscles were subjected to 20‐min no‐flow ischaemia followed by 60‐min reperfusion (I/R). I/R significantly decreased the contraction in untreated preparations (control group, 34±4% of baseline value, n=6). Brief administration of JT (1.0 μM) prior to ischaemia significantly improved the postischaemic contractile recovery (63±5% of baseline value, n=4), as compared to the control group. JT (1.0 μM) slightly prolonged action potential duration before ischaemia and induced conduction disturbance (2 : 1 block) after the initiation of ischaemia. The cardioprotective effect of JT was antagonized by chelerythrine (CH, 5.0 μM), an inhibitor of protein kinase C (PKC) or by 5‐hydroxydecanoic acid (5‐HD, 400 μM), an inhibitor of mitochondrial ATP‐sensitive K+ (KATP) channels. These results suggest that the protective effect of JT is due to the opening of mitochondrial KATP channels, which, in turn, is linked to PKC activation.

Mexiletine-induced shortening of the action potential duration of ventricular muscles by activation of ATP-sensitive K+ channels

A class Ib antiarrhythmic drug, mexiletine (100 μM) significantly shortened the action potential duration (APD) of guinea‐pig ventricular muscles and this effect was completely abolished in the presence of glibenclamide (50 μM), a blocker of the ATP‐sensitive K+ channel (KATP)‐ Mexiletine significantly increased the open probability of uridine diphosphate‐primed KATP channels, recorded in inside‐out patches of the ventricular cells. The results suggest that mexiletine shortens the APD of ventricular muscles, at least in part, via activation of KATP.

Rate-Dependent prolongation of action potential duration in single ventricular myocytes obtained from hearts of rats with streptozotocin-induced chronic diabetes sustained for 30–32 weeks

SummaryWe examined the characteristics of the action potentials of single ventricular myocytes obtained from the hearts of rats with chronicallyinduced diabetes. Male Wistar rats were made diabetic by injecting streptozotocin (65mg/kg) and 30–32 weeks later the hearts were excised and used for an electrophysiological study. Action potentials were recorded from isolated right ventricular myocytes by an electrode fabricated for patch clamp in the wholecell recording configuration. The action potential durations (APDs) of steady state chronic diabetic rat myocytes were longer than those of age-matched normal rat myocytes at all levels of repolarization (APD25, APD50, APD75, and APD90). As the stimulation frequency was increased (0.2–2Hz), the APDs were lengthened in both diabetic and normal rats, and the difference of APDs between the groups was greater when the stimulation frequency was higher. When we examined alterations of APDs under conditions of train stimulation (2Hz, 20 stimuli), (1) the APDs in both groups were prolonged, and (2) the degree of prolongation of APD was significantly greater and the rate of APD prolongation was significantly faster in myocytes from the diabetic rats. The prolongation of APD in these heart cells is probably secondary to alteration of the transient outward current Ito, and sheds light on repolarization abnormality in cases of diabetic cardiomyopathy.

Dynamics of T-U wave in patients with idiopathic ventricular tachycardia originating from the right ventricular outflow tract

Postextrasystolic U wave augmentation is observed in patients with long QT syndrome and those with organic heart disease. This phenomenon is considered a marker of increased risk of arrhythmia. However, the characteristics of the U wave have not been evaluated in patients with idiopathic VT originating from the right ventricular outflow tract (RVOT‐VT). The present study evaluated the dynamic change in the T‐U wave in patients with RVOT‐VT. Holter ECGs obtained from 14 patients with RVOT‐VT and 11 healthy control subjects were analyzed. The amplitude of T and U waves (Tamp and Uamp) and preceding RR intervals were measured during stable sinus rhythm (rate dependent change) and in the postextrasystolic sinus complex (pause dependent change). Uamp correlated negatively and significantly with the preceding RR interval in 13 (93%) RVOT‐VT patients but in only 2 (18%) control subjects. The average value of the slope of the Uamp/RR relationship was negative (−0.22 ± 0.10 mV/s) in the RVOT‐VT group, but was positive (0.04 ± 0.07 mV/s, P < 0.001) in the control group. Pause dependent U wave augmentation was observed in 12 (86%) of 14 patients. Increased frequency of consecutive preceding premature ventricular contractions (PVCs) was associated with a larger postextrasystolic Uamp. PVC or the first ventricular beat of VT arose from near the peak of augmented U waves. The dynamic changes in the T‐U wave were observed in patients with RVOT‐VT. Further investigations are required to elucidate the precise role of the U wave in arrhythmogenesis in those patients. (PACE 2004; 27:148–155)

Class I antiarrhythmic drugs alter the severity of myocardial stunning by modulating ATP-sensitive K+ channels in guinea pig ventricular muscles

The effects of various class I antiarrhythmic drugs and glibenclamide were examined on the recovery of contraction during reperfusion, in relation to the action potential duration (APD) seen during ischemia. Action potential and contractile tension were recorded from isolated guinea pig right ventricular muscles perfused with oxygenated Tyrode solution via the coronary artery. Ten minutes of no-flow ischemia shortened the APD at 90% of repolarization level (APD90) to 58% of control (pre-ischemic values). The APD90 was completely restored after 60 min of reperfusion. The developed tension was abolished during ischemia and recovered to 87% of control after 60 min of reperfusion. In the presence of Vaughan Williams class Ia drug cibenzoline (5 μM) or an ATP-sensitive potassium (KATP) channel blocker glibenclamide (10 μM), the shortening of the APD90 during ischemia was significantly attenuated. However, the recovery of developed tension was significantly inhibited. Class Ic drug pilsicainide (10 μM) did not affect the ischemia-induced shortening of the APD90 or the recovery of developed tension after reperfusion. In the presence of class Ib drug mexiletine (10 μM), the shortening of the APD90 during ischemia was significantly facilitated. The recovery of developed tension in the presence of mexiletine tended to be improved, although the difference was not statistically significant. The developed tension measured after the 60 min reperfusion period following 20 min of no-flow ischemia was markedly depressed, indicating the presence of myocardial stunning. Mexiletine and pilsicainide significantly improved the recovery of developed tension and diminished the stunning. We conclude that cibenzoline and glibenclamide, which block cardiac KATP channels inhibit contractile recovery after reperfusion by attenuating the shortening of APD during ischemia. In contrast, mexiletine, which activates KATP channels (in addition to blockade of Na+ channels) improves contractile recovery by facilitating the shortening of APD during ischemia.