The renoprotective effect of esaxerenone independent of blood pressure lowering: a post hoc mediation analysis of the ESAX-DN trial

Angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) are recommended as first-line drugs for hypertension with diabetic nephropathy owing to their renoprotective effect; however, their effect beyond lowering blood pressure (BP) has not been confirmed. Recent studies have shown that aldosterone plays a key role in causing renal injury; therefore, it is likely that mineralocorticoid receptor (MR) blockers inhibit aldosterone-induced renal damage in different ways from ACE inhibitors and ARBs. Therefore, we investigated the mechanism of the effect of an MR blocker on reducing the urinary albumin-to-creatinine ratio (UACR) using data from a randomized, double-blind, placebo-controlled phase 3 study (ESAX-DN) of a new nonsteroidal MR blocker, esaxerenone. This post hoc analysis used a novel statistical method to quantitatively estimate the effect of esaxerenone on UACR reduction mediated, or not mediated, by changes in systolic BP (SBP) and/or estimated glomerular filtration rate (eGFR). The proportion of the mediated effect by SBP changes to the total effect on UACR reduction was 9.8-10.7%; the UACR was reduced to 0.903-0.911 times the baseline at the end of treatment through the SBP-related pathway and to 0.422-0.426 times the baseline through the non-SBP-related pathway. Even considering both SBP and eGFR simultaneously, the proportion of the mediated effect was 21.9-28.1%. These results confirm that esaxerenone has a direct UACR-lowering effect independent of BP lowering and that its magnitude is much larger than that of the BP-dependent effect. Thus, esaxerenone could be a UACR-reducing treatment option for patients with diabetic nephropathy.

Reduction in the magnitude of serum potassium elevation in combination therapy with esaxerenone (CS-3150) and sodium-glucose co-transporter-2 inhibitor in patients with diabetic kidney disease: Subanalysis of two phase 3 studies

AIMS/INTRODUCTION

We evaluated the effect of co-administration of esaxerenone and a sodium-glucose cotransporter 2 (SGLT2) inhibitor on the magnitude of serum potassium elevation in Japanese patients with diabetic kidney disease.

MATERIALS AND METHODS

We conducted a prespecified subanalysis of data from two phase 3 studies: a multicenter, randomized, double-blind, placebo-controlled trial in patients with type 2 diabetes and microalbuminuria (J308); and a multicenter, single-arm, open-label trial in patients with type 2 diabetes and macroalbuminuria (J309). Changes in serum potassium levels during the studies and other measures were evaluated according to SGLT2 inhibitor use.

RESULTS

In both studies, time course changes in serum potassium levels, and incidence rates of serum potassium elevation were lower in patients with co-administration of SGLT2 inhibitor in both the placebo and esaxerenone groups than those without the inhibitor. In contrast, time course changes and mean percent changes from baseline in urinary albumin-to-creatinine ratio (UACR), the proportion of patients with albuminuria remission, and time course changes in blood pressure did not change with or without SGLT2 inhibitor, while UACR and blood pressure were reduced with esaxerenone. The blood glucose-lowering effect of SGLT2 inhibitor was not affected by esaxerenone.

CONCLUSIONS

In Japanese patients with type 2 diabetes and albuminuria treated with esaxerenone, concomitant use of SGLT2 inhibitor reduced the magnitude of serum potassium elevation without any change of its antihypertensive and albuminuria-suppressing effects. Co-administration of esaxerenone and SGLT2 inhibitor may be a beneficial treatment option for patients with diabetic kidney disease.

Esaxerenone (CS-3150) in Patients with Type 2 Diabetes and Microalbuminuria (ESAX-DN): Phase 3 Randomized Controlled Clinical Trial

BACKGROUND AND OBJECTIVES

Diabetic kidney disease is an important complication of type 2 diabetes. In a phase 2b study, adding esaxerenone to renin-angiotensin system inhibitors dose dependently reduced the urinary albumin-to-creatinine ratio in patients with type 2 diabetes and microalbuminuria. This 52-week phase 3 study further investigated the effects of esaxerenone on the urinary albumin-to-creatinine ratio in this patient group.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this multicenter, randomized, double-blind study, patients with type 2 diabetes and a urinary albumin-to-creatinine ratio of 45 to <300 mg/g creatinine treated with renin-angiotensin system inhibitors were randomized to esaxerenone or placebo for 52 weeks (n=455). Esaxerenone was initiated at 1.25 mg/d and titrated to 2.5 mg/d on the basis of serum potassium monitoring. The primary endpoint was the proportion of patients achieving urinary albumin-to-creatinine ratio remission (<30 mg/g creatinine and ≥30% reduction from baseline on two consecutive occasions).

RESULTS

Overall, 49 (22%) and nine (4%) patients in the esaxerenone and placebo groups, respectively, achieved urinary albumin-to-creatinine ratio remission (absolute difference 18%; 95% confidence interval, 12% to 25%; P<0.001). The percent change in urinary albumin-to-creatinine ratio from baseline to end of treatment was significantly higher with esaxerenone versus placebo (-58% versus 8%; geometric least-squares mean ratio to placebo 0.38, 95% confidence interval, 0.33 to 0.44). There was a significant improvement with esaxerenone versus placebo in time to first remission (hazard ratio, 5.13; 95% confidence interval, 3.27 to 8.04) and time to first transition to urinary albumin-to-creatinine ratio ≥300 mg/g creatinine (hazard ratio, 0.23; 95% confidence interval, 0.11 to 0.48). More patients had a serum potassium level ≥6.0 or ≥5.5 mEq/L on two consecutive measurements in the esaxerenone group (20 [9%]) versus placebo (5 [2%]); these events were asymptomatic and resolved after dosage reduction or treatment discontinuation.

CONCLUSIONS

Adding esaxerenone to existing renin-angiotensin system inhibitor therapy in patients with type 2 diabetes and microalbuminuria increased the likelihood of albuminuria returning to normal levels, and reduced progression of albuminuria to higher levels.

Efficacy and Safety of Esaxerenone (CS-3150) for the Treatment of Type 2 Diabetes with Microalbuminuria: A Randomized, Double-Blind, Placebo-Controlled, Phase II Trial

BACKGROUND AND OBJECTIVES

The progression of kidney disease in some patients with type 2 diabetes mellitus may not be adequately suppressed by renin-angiotensin system inhibitors. Esaxerenone (CS-3150) is a nonsteroidal mineralocorticoid receptor blocker that has shown kidney protective effects in preclinical studies, and it is a potential add-on therapy to treat diabetic kidney disease. This phase 2 study evaluated the efficacy and safety of esaxerenone in Japanese patients with type 2 diabetes mellitus and microalbuminuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This multicenter, randomized, double-blind, placebo-controlled trial enrolled 365 hypertensive or normotensive patients with type 2 diabetes mellitus and microalbuminuria (urinary albumin-to-creatinine ratio ≥45 to <300 mg/g creatinine) treated with renin-angiotensin system inhibitor who had eGFR≥30 ml/min per 1.73 m². Participants were randomized to receive 0.625, 1.25, 2.5, or 5 mg/d esaxerenone or placebo for 12 weeks. The primary end point was the change in urinary albumin-to-creatinine ratio from baseline to week 12 (with last observation carried forward).

RESULTS

Esaxerenone treatment at 1.25, 2.5, and 5 mg/d significantly reduced urinary albumin-to-creatinine ratio by the end of treatment (38%, 50%, and 56%, respectively) compared with placebo (7%; all P<0.001). The urinary albumin-to-creatinine ratio remission rate (defined as urinary albumin-to-creatinine ratio <30 mg/g creatinine at the end of treatment and ≥30% decrease from baseline) was 21% in the 2.5- and 5-mg/d groups versus 3% for placebo (both P<0.05). Adverse events occurred slightly more frequently with esaxerenone versus placebo, but the frequencies of drug-related adverse events and discontinuation rates were similar in the placebo and the 0.625-, 1.25-, and 2.5-mg/d groups. Drug-related adverse events and treatment discontinuations were marginally higher in the 5-mg/d group. The most common drug-related adverse event was hyperkalemia, which was dose proportional.

CONCLUSIONS

Adding esaxerenone at 1.25, 2.5, and 5 mg/d for 12 weeks to an ongoing renin-angiotensin system inhibitor significantly reduces urinary albumin-to-creatinine ratio in patients with type 2 diabetes mellitus and microalbuminuria.

Successfully Treated Unstable Angina Pectoris in a Young Japanese Female

A 25-year-old Japanese female complaining chest oppression and palpitation was admitted to hospital under the presumptive diagnosis of ischemic heart disease (IHD), although no obvious underlying disease associated with IHD was detected. Coronary angiography showed stenosis at the proximal site of left anterior descending artery (LAD), with dilatation and tortuosity at the bifurcation of the first and the second septal branches. Intravascular ultrasound imaging of the LAD showed intimal thickness without calcification at the site of stenosis. The stenosis was successfully and smoothly dilated by percutaneous transluminal angioplasty. Even with precise evaluation, the cause of the coronary artery disease in this young female patient was not clarified. Further careful follow-up is needed.

Improvement of exercise tolerance by single lead VDD pacemaker: evaluation using cardiopulmonary exercise test

We used a cardiopulmonary test to assess the physiological benefit of single lead VDD pacing in ten patients (six men, four women; aged 32-84 years, mean 69 years) with atrioventricular block. Maximal symptom-limited treadmill exercise test using a ramp protocol was performed under VDD and VVIR or VVI pacing (VVI) in random sequence. The pacemaker was then programmed to the VDD mode, and Holter ECG was recorded in nine patients. Compared with findings during the VVI, the VDD mode had a greater chronotropic response (mean maximal heart rate, VDD 106 +/- 17 beats/min vs VVI 79 +/- 19 beats/min, P = 0.03), and was associated with prolongation of exercise duration (VDD 11.2 +/- 2.9 minute vs VVI 10.5 +/- 3.1 minute; P = 0.01), and the onset of anaerobic threshold at a higher oxygen uptake (VDD 12.4 +/- 3.4 mL/min per kilogram vs VVI 10.0 +/- 2.1 mL/min per kilogram; P < 0.01). Atrial sensing was recognized in almost all normal sinus P waves for all cases examined using Holter ECG. Thus, chronotropic response during exercise by VDD pacemaker improved exercise tolerance, indicating that a VDD pacemaker might be useful for patients requiring physical activity.

Hypertrophic cardiomyopathy complicated with cardiac amyloidosis

The echocardiographic findings of hypertrophic cardiomyopathy (HCM) are very similar to those of cardiac amyloidosis. A 76-year-old Japanese man was admitted for treatment of early stage gastric cancer in July 1996. His electrocardiogram indicated left ventricular hypertrophy and echocardiography showed left ventricular hypertrophy with asymmetric septal hypertrophy. He was re-admitted complaining of dyspnea on effort and pretibial edema in October 1998. The amplitude of QRS complex on electrocardiogram was decreased. Echocardiogram showed left ventricular wall thickening with granular sparkling. He was diagnosed as HCM with cardiac amyloidosis.

Analysis of T wave changes by activation recovery interval in patients with atrial septal defect

We examined the distributions of the activation recovery interval (ARI), which is correlated with the local action potential duration (APD), to clarify the origin of the repolarization changes in ASD. The ECGs, QRST isointegral maps and ARI isochronal maps of 21 children with ASD from 3 to 5 years old in age were studied in comparison with 21 age-matched normal children. A conventional and 87 unipolar body surface ECG were simultaneously recorded. The ARIs were determined from the first derivatives of the ECG waveforms. Abnormal ST-T patterns were observed in 11 of 21 ASD, but only in two normal children. The QRST maps of a split positive area pattern were seen in 15 of ASD but none of the normal. In the ARI maps, all the normal children exhibited a short-ARI area on the left and a long-ARI area on the right side of the chest. In 19 of ASD, the ARI distribution revealed a leftward extension of the long-ARI area on the anterior chest, a relative shortening on the right anterior chest, and a localized prolonged ARI on the left anterior chest. The results suggest that right ventricular (RV) volume overload in ASD produces a localized prolongation of the APD on the RV epicardium.

Cardiac arrhythmias and left ventricular hypertrophy in dipper and nondipper patients with essential hypertension

To evaluate the behavior of cardiac arrhythmias in dipper and nondipper hypertensive patients, 48-h ambulatory blood pressure monitoring, 24-h Holter electrocardiogram recording and echocardiographic studies were performed in 56 untreated outpatients with essential hypertension. These patients were divided into 2 groups according to the presence (dipper, n=33) or absence (nondipper, n=23) of reduction of both systolic and diastolic blood pressure during nighttime by an average of more than 10% of daytime blood pressure. Mean 48-h systolic and diastolic blood pressures did not differ between the 2 groups. Nondipper patients had a significantly larger left atrial dimension (31.9+/-3.8 vs 35.6+/-3.7 mm; p<0.01), left ventricular mass index (114+/-26 vs 136+/-36 g/m2; p<0.05), as well as a larger number of total supraventricular (16+/-19 vs 89+/-197 beats; p<0.05) and ventricular ectopic beats (7+/-14 vs 47+/-96 beats; p<0.05) during daytime as compared with dippers. In conclusion, nondipper hypertensive patients are likely to experience supraventricular and ventricular arrhythmias more frequently than dippers. A blunted nocturnal blood pressure fall may be involved in the appearance of cardiac arrhythmias in patients with essential hypertension.

Pathological findings of the isthmus between the inferior vena cava and tricuspid annulus ablated by radiofrequency application

Anatomically guided radiofrequency ablation for the treatment of atrial flutter was performed in a 41-year-old man with interstitial pneumonia. He died of respiratory failure 2 months after ablation, and an autopsy was performed. The whole layer of the ablation site showed a transluminal fibrosis.

The inhibitory effects of carvedilol against arrhythmias induced by coronary reperfusion in anesthetized rats

BACKGROUND

Previous study has shown the antiarrhythmic effects of carvedilol on isolated rat hearts, but little is known about the mechanism of this protective action. This article examines the inhibitory effect of carvedilol against arrhythmias induced by reperfusion in anesthetized rats. In addition, the results are compared with those with propranolol, superoxide dismutase (SOD) plus catalase, and a combination of both in order to elucidate the mechanism of the protective actions.

METHODS AND MATERIALS

Ninety percent of the rats in the control group showed lethal ventricular fibrillation (VF). Carvedilol at the doses of 0.03, 0.1, and 0.3 mg/kg significantly reduced the incidence of lethal VF to 0%, 0%, and 10%, respectively (P <.05). In contrast, propranolol at the doses of 0.3, 1.0, and 3.0 mg/kg and SOD (35,000 units/kg) plus catalase (400,000 units/kg) did not reduce the incidence of lethal VF (80%, 60%, 70%, and 70%, respectively). However, administration of a combination of propranolol (1.0 mg/kg) and SOD plus catalase completely inhibited the occurrence of lethal VF to 0% (P<.05).

CONCLUSION

These results indicate that carvedilol has the inhibitory effect against reperfusion arrhythmias in rats and suggest that the mechanism of action of this compound is related to the combined effects of beta-blocking and antioxidant.

Successfully treated complete atrioventricular block with corticosteroid in a patient with cardiac sarcoidosis: usefulness of gallium-67 and thallium-201 scintigraphy

A 71-year-old male with sarcoidosis was followed for 6 years without steroid therapy. He was admitted because of complete atrioventricular block. Chest X-ray showed hilar lymphadenopathy. Echocardiogram showed mild left ventricular hypertrophy without local wall thinning. Cardiac sarcoidosis was diagnosed by a defect of Thallium-201 (Tl-201) imaging and abnormal uptake of Gallium-67 (Ga-67). After the start of corticosteroid therapy, complete atrioventricular block was recovered. Abnormal uptake of Ga-67 was improved. Tl-201 and Ga-67 are useful to diagnose cardiac sarcoidosis, to evaluate the lesion of cardiac involvement and to estimate the efficacy of corticosteroid therapy.

Effect of imidapril in dipper and nondipper hypertensive patients: comparison between morning and evening administration

The purpose of the study was to identify differences in the patterns of efficacy and duration of effects of imidapril administered at different times of the day (morning versus evening) in dipper and nondipper hypertensive patients. Twenty patients with untreated hypertension were classified into two groups: dippers (n = 9) and nondippers (n = 11). Imidapril (10 mg) was given at 07:00 or 18:00 for 4 weeks in a crossover fashion. Blood pressure (BP) and heart rate (HR) were monitored before and after morning and evening treatment every 30 min for 48h by ambulatory BP monitoring (ABPM). In dipper hypertension, the mean 48h BP was reduced with both doses. The decrease in the diurnal BP was stronger when the drug was administered in the evening than morning, but without significant difference. In nondipper hypertension, the systolic BP decreased at night with both doses, but the extent of the nocturnal reduction in systolic BP was greater after morning therapy. There were no significant differences in the decrease in BP during the day or night between the morning and evening administrations. When imidapril was administered in the morning, its serum concentration reached a maximum at 16:00, and when the drug was administered in the evening, it reached a maximum at 6:00. In dipper hypertension, the time taken for the blood concentration of imidapril to reach a maximum changed depending on its time of administration, and the time when the maximum antihypertensive effect of the drug appeared was different. In nondipper hypertension, decreases in the BP were confirmed at night regardless of the time of administration; this might be caused by angiotensin converting enzyme (ACE) inhibitors effectively blocking the BP from increasing by activating the parasympathetic nervous system. Therefore, when assessing the effectiveness of antihypertensive agents, factors such as the various patterns of BP before therapy and administration time must be considered.

Relation between QT interval dispersion and heart rate

Because the relation between QT dispersion (QTd) and heart rate (HR) are different from that between QT interval and HR, QTd could be overadjusted at a high HR and be underadjusted at a slow HR if we use Bazett's formula to adjust QTd. HR adjustment of QTd is not needed to evaluate repolarization dispersion.

Antiarrhythmic effect of magnesium sulfate against occlusion-induced arrhythmias and reperfusion-induced arrhythmias in anesthetized rats

The antiarrhythmic effect of magnesium sulfate (Mg) as well as the hemodynamics were studied using the coronary ligation and reperfusion models in rats. In the study on coronary ligation arrhythmia, i.v. administration of Mg (0.6, 2, 6, 20 and 60 micromol) was conducted at 5 min after coronary ligation. Mg had an action to decrease the total number of premature ventricular contraction (PVC), the duration of ventricular tachycardia (VT), the frequency of VT and ventricular fibrillation (Vf) and the mortality ratio for 30 min after coronary ligation. In the 6-60 micromol groups, significant antiarrhythmic action (p < 0.01 vs. control) was attained. In the study on reperfusion arrhythmia, i.v. administration of Mg (20, 60 and 200 micromol) was conducted at 4 min after coronary ligation, and at 1 min after ligation, the coronary artery was reperfused. Mg had an action to decrease the frequency of Vf, the mortality ratio and the duration of VT and Vf and to extend the interval between the initiation of reperfusion and the occurrence of VT and Vf for 10 min after reperfusion. In the 200 micromol group, significant antiarrhythmic action (p < 0.05 vs. control) was attained. Administration of Mg decreased the heart rate and blood pressure. We concluded that Mg can control myocardial ischemia-induced and reperfusion-induced arrhythmia and that sudden cardiac death which occurs as a result of arrhythmia can be prevented.

Exercise-induced uncommon atrioventricular nodal reentrant tachycardia with sick sinus syndrome: a case report

Exercise seldom provokes tachycardia in patients with paroxysmal supraventricular tachycardia (PSVT). This report presents a case of exercise-induced uncommon atrioventricular nodal reentrant tachycardia (AVNRT) with sick sinus syndrome. Treadmill exercise testing provoked AVNRT of long RP' with good reproducibility. Uncommon AVNRT was confirmed by the lack of atrial pre-excitation during PSVT and para-Hisian pacing. The patient has been successfully treated with verapamil and DDD pacing for 5 years.

Alterations of autonomic nervous activity in recurrence of variant angina

OBJECTIVE

To investigate whether autonomic nervous activity is involved in the recurrence of spontaneous coronary spasm in variant angina.

DESIGN

Retrospective analysis.

SETTING

Cardiology department of a university hospital.

PATIENTS

18 patients with variant angina were divided into single attack group (SA; nine patients) and multiple attack group (MA; nine patients) according to the frequency of ischaemic episodes with ST segment elevation during 24 hour Holter monitoring.

METHODS

Heart rate variability indices were calculated using MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non-linear least squares method for fitting analysis, at 30 second intervals for 30 second periods, from 40 minutes before the attack to 30 minutes after the attack. High frequency (HF; 0.04-0.15 Hz) was defined as a marker of parasympathetic activity, and the ratio of low frequency (LF; 0.15-0.40 Hz) to high frequency (LF/HF) as an indicator of sympathetic activity. The averaged value during the 40 to 30 minute period before an attack was defined as the baseline.

RESULTS

Compared with baseline, the HF component decreased in both groups at two minutes before the attack (p < 0.01), and the LF/HF ratio decreased at three minutes before the attack (p < 0.01). The baseline LF/HF was lower in the MA group than in the SA group (p < 0. 01).

CONCLUSIONS

A reduction of sympathetic activity may play a key role in determining the recurrence of transient ischaemic events caused by spontaneous coronary spasm in patients with variant angina.

Non-dipolarity of heart potentials estimated by magnetocardiography in normal subjects

We studied non-dipolarity characteristics during ventricular excitation in normal adults and children by magnetocardiography (MCG) by recording magnetic field on the thorax. The source and currents of the electrical dipole from the onset up to 60 ms of ventricular excitation were analyzed in 16 adults and 5 children. A single equivalent current dipole (ECD) was estimated by Sarvas' formula for the sphere model at 1 ms intervals. The non-dipole value (NDV) was calculated from the magnetic field strength at each recording point and theoretically estimated by ECD, representing an index for the non-dipolarity. At 32-34 ms from the beginning of QRS, the mean NDV was a minimum in all subjects suggesting at least a non-dipole component during this period. High NDV (over 5%) were present in most subjects in both the early and late phase compared to this period. Thirteen of 16 adults had a high NDV in the early phase (9.3 +/- 3.0%, mean +/- SD) and all 16 subjects had a high NDV in the late phase (21.5 +/- 10.5%). All 5 children had high NDV in both the early (10.5 +/- 5.4%) and late phases (16.8 +/- 7.9%). A single ECD estimation by MCG showed a relatively low non dipolar component and MCG could be applied to the clinical evaluation of cardiac excitation in both normal and pathological conditions.

[Differences in exercise blood pressure response between dipper and non-dipper elderly patients with essential hypertension]

We evaluated the circadian variation and exercise stress response patterns of blood pressure (BP) in elderly patients with essential hypertension. Ambulatory BP monitoring for 48 hours every 30 minutes, and treadmill exercise test using a Bruce protocol at PM 3 to 5 were performed in 49 untreated patients with hypertension. Mean daytime (awake), and night-time (sleeping) systolic BP (SBP) and diastolic BP (DBP) values were analyzed by reviewing the patients' diaries, and the nocturnal reduction rate (NRR) of SBP and DBP were calculated according to the following formula. NRR (%) = [(daytime mean-nighttime mean)/daytime mean] x 100. The patients were divided into two groups according to the presence (dipper, n = 25) or absence (non-dipper, n = 24) of a reduction in both SBP and DBP during the night by an average of more than 10% of the daytime BP. Mean values of SBP and DBP measured over 48 hours in the dipper and non-dipper groups were similar. Responses of SBP to dynamic exercise at 2 to 5 minutes in the non-dipper group were significantly smaller than those in the dipper group (p < 0.05). Non-dipper patients with hypertension responded to dynamic exercise stress with smaller increases in SBP than did those in the dipper group. The differences in BP responses to exercise may affect the circadian blood pressure profile in dipper and non-dipper elderly patients with essential hypertension.

Exercise-induced monomorphic ventricular tachycardia from the left ventricle outflow tract

A case of exercise-induced idiopathic ventricular tachycardia (VT) arose from the left ventricular outflow tract. The QRS morphology of the VT was Rs pattern in V1 and R pattern in the lateral leads with inferior axis. The pacing at the superior interventricular septum near the mitral anulus produced the best pace mapping. Radiofrequency application to this site suppressed the VT.

Dipyridamole thallium-201 single-photon emission computed tomography for prediction of perioperative cardiac events in patients with arteriosclerosis obliterans undergoing vascular surgery

The aim of the study was to determine whether or not dipyridamole thallium-201 single-photon emission computed tomography (201Tl-SPECT) has significant additive value for predicting perioperative cardiac events in patients with arteriosclerosis obliterans (ASO) undergoing vascular surgery. Routine preoperative 201Tl-SPECT was performed in 106 consecutive patients with ASO (age 68+/-8.9 years; 91 men and 15 women). The frequency of reversible defects in a clinical high-risk group (n=44) was significantly higher than in a low-risk group (n=62; 55% vs 24%, p<0.01). Perioperative cardiac events occurred in 9 patients, including 4 cardiac deaths, 1 non-fatal myocardial infarction, and 4 cases of unstable angina. Although clinical risk stratification was useful in predicting cardiac events (19% in the high-risk group vs 2% in the low-risk group, p<0.01), the positive predictive value was low. When considering a combination of 2 or more than 2 risk factors and a large reversible defect as a predictor, the positive predictive value and specificity increased from 19% to 47% and from 64% to 91%, respectively, whereas the sensitivity remained unchanged (89%). These results suggest that the addition of 201Tl-SPECT data to clinical risk-stratified patients with ASO allows better prediction of perioperative cardiac events.

Prevalence of ventricular preexcitation in Japanese schoolchildren

BACKGROUND

Wolff-Parkinson-White syndrome is thought to be a congenital disease, however, its exact prevalence is not known. This may be because of the intermittent activity of accessory pathways in some cases and fluctuations in autonomic tone.

AIMS

To investigate the prevalence of ventricular preexcitation by electrocardiography and reported symptoms in each school age child in Yamanashi prefecture.

METHODS

From 1994 to 1996, answers to a questionnaire, results of physical examination, and electrocardiography were obtained from all schoolchildren in Yamanashi prefecture (n = 92,161; total population 880,000) on admission to elementary school (age 6 to 7 years, n = 28,395), junior high school (age 12 to 13 years, n = 31,206), and high school (age 14 to 15 years, n = 32,837).

RESULTS

Elementary and junior high school students had a significantly lower prevalence of preexcitation than high school students (0.073% and 0.070% v 0.174%, p < 0.001). The prevalence of left free wall pathway was highest in high school students (n = 27) compared with elementary (n = 6) and junior high school students (n = 5) (p < 0.005). The only symptom noted in the answers to the questionnaire was palpitations. The symptomatic cases were more frequent in high school (n = 13) than in elementary (n = 1) and junior high school (n = 2) children, but not significantly. No student with preexcitation had associated heart disease or family history of Wolff-Parkinson-White syndrome or sudden death.

CONCLUSIONS

The prevalence of preexcitation in younger schoolchildren was less frequent than previously reported. The prevalence of preexcitation and left free wall pathways increased with age. The symptoms were few and there was no significant morbidity.

Multiple modulations of action potential duration by different calcium channel blocking agents in guinea pig ventricular myocytes

Effects of extracellular applications of different types of Ca2+ channel blocking agents (Mn2+, verapamil, and nisoldipine) on action-potential duration and membrane currents were studied by the whole-cell patch-clamp technique in guinea pig ventricular myocytes. Low concentrations of Mn2+ (1 mM) and verapamil (1 microM) prolonged action-potential duration at 90% repolarization (APD90) with a suppressed plateau phase. Increases in Mn2+ (5 mM) and verapamil (5 microM) shortened APD90 with a further depression of the plateau. Nisoldipine (0.2-1 microM) shortened APD90 without lengthening it. Applications of Mn2+ and verapamil suppressed amplitudes of the L-type Ca2+ current (ICa), the delayed outward K+ current (IK), and the inward rectifier K+ current (IK1). Furthermore, the ratios of ICa:IK inhibition were similar by low and high concentrations of Mn2+ and verapamil. Nisoldipine selectively suppressed ICa without effect on IK and IK1. A low concentration (1 mM) of Mn2+ not only decreased the peak amplitude of ICa but also delayed its decay time course, which caused an increase in late ICa amplitude at the end of a 200-ms depolarizing pulse. Both verapamil and nisoldipine suppressed peak ICa without affecting its decay. Whereas Mn2+ suppressed IBa without changing its decay time course, verapamil and nisoldipine speeded up the IBa decay with suppressed amplitude of IBa. We conclude that different types of Ca2+ channel blocking agents (Mn2+, verapamil, and nisoldipine) diversely modulate APD because of their multiple modes of actions on ICa and IK.

Precordial leads QRST time integrals for evaluation of right ventricular overload in children with congenital heart diseases

It was previously shown that body surface QRST isointegral maps of the anterior chest were abnormal in patients with right ventricular overload and that the abnormalities varied with hemodynamic status. The QRST isointegral maps were first characterized by using a departure index map for normal controls. The study group consisted of 14 patients with pulmonary stenosis (PS), 20 with tetralogy of Fallot, (TOF) and 43 with atrial septal defect (ASD). The QRST isointegral maps of these three groups were compared with the data on 23 to 65 age-matched normal children. In mean departure index maps, the patients with right ventricular pressure overload (PS or TOF) showed an increase in departure index on the anterior midchest, while those of right ventricular volume overload (ASD) showed two maxima on the anterior and left lateral chest, with a trough-like negative area between them. Since the abnormal findings were seen on the anterior chest, we evaluated the diagnostic usefulness of QRST time integral values for precordial leads of the routine electrocardiogram (ECG) in a second part of this study. The precordial QRST time integral values from 9 patients with PS and 11 with TOF (0-2 years of age, mean 1.1 years) and 22 ASD patients (6-15 years, mean 10.1 years) were compared with those of the age-matched control children. The QRST time integral values of the precordial leads in right ventricular pressure overload were significantly increased in the right precordial leads (V1, V2). In right ventricular volume overload, the QRST time integral values of the V1, V2, V4, and V6 leads demonstrated a significant deviation from those of the control group. Therefore, a discrimination formula was constructed by using the values of these leads, and the criteria derived from this formula revealed good (98%) diagnostic accuracy. In detection of right ventricular overload, the QRST time integral values of the precordial lead ECG, if confirmed in a larger data set, may be useful as a simple screening method.

Effects of antiarrhythmic agents and Mg2+ on aconitine-induced arrhythmias

The effects of antiarrhythmic agents, including Classes I and IV and 3-10 mM Mg2+ on aconitine-induced arrhythmias were examined using a conventional microelectrode and patch clamp method in Langendorff-perfused rabbit hearts and isolated guinea-pig ventricular myocytes. Intracoronary application of 0.1 microM aconitine induced polymorphic ventricular tachycardia (PVT) which continued for more than 60 minutes. Application of aconitine to ventricular myocytes caused a prolonged action potential duration (APD) and the appearance of early afterdepolarization (EAD) together with the occurrence of an inward hump of the I-V curve around -60 to -40 mV and increased outward current at positive voltages. Application of 10 microM TTX and 5 mM or higher Mg2+ restored aconitine-induced PVT to sinus rhythm in Langendorff-perfused preparations and also shortened the prolonged APD, demonstrating the abolishment of EAD by aconitine in ventricular myocytes. However, antiarrhythmic agents did not exert such effects. In conclusion, the antiarrhythmic actions of Mg2+ and TTX in aconitine-induced arrhythmia are to abolish EAD and shorten the prolonged APD by suppression of the inward Na+ current around -60 to -40 mV.

Functions of cardiac ion channels under normal and pathological conditions

Using the patch clamp technique, normal and abnormal functions of cardiac ion channels were studied. The transient outward K+ current contributes to the early repolarization phase of the action potential as well as to the plateau height and total duration. The latter role is observed in at premature excitations due to slow recovery from inactivation of this current compared to that of the Ca2+ current. Early and delayed afterdepolarizations are produced by multiple components of ionic currents, especially in the former case. Transient inward current is mainly involved in the formation of delayed afterdepolarizations, but the activities can be produced by a different ionic mechanism in rare occasions. Barium-induced automaticity can be brought about by blocking and unblocking of the inward rectifier K+ channels. The ATP-sensitive K+ channels are assumed to play important roles in myocardial ischemia and related conditions. The channels are a target of the K+ channel openers and their functions are modulated by various intracellular factors. While the channel activity is strongly inhibited by intracellular ATP, ATP is necessary for the channel in an operative state. The former effect by ATP is produced by its ligand action, but the latter may be brought about by hydrolysis of MgATP, which may be regulated by the assembly and disassembly of the actin cytoskeleton.

Electrophysiological effects of clentiazem, a new Ca2+ antagonist, on rabbit hearts

Electrophysiological effects of clentiazem, a new 1,5-benzothiazepine type Ca(2+) antagonist, were examined in comparison with those of diltiazem in excised rabbit heart preparations. In Langendorff-perfused hearts electrically driven at basic cycle lengths of 400-500 ms, clentiazem (10(-8)-10(-6)M) and diltiazem (10(-8)-10(-6)M) caused a concentration-dependent prolongation of the atrio-His bundle conduction time (A-H interval) without affecting the His bundle-ventricular conduction time (H-V interval). The effects of clentiazem were equivalent to those of diltiazem. In isolated rabbit atrioventricular (A-V) node preparations electrically driven at 400- to 500-ms intervals, clentiazem and diltiazem at >10(-6)M concentrations produced concentration-dependent decreases in action potential amplitude (APA), maximum rate of depolarization (V max), and shortened action potential duration at 20 and 50% repolarization (APD(20) and APD(50)), whereas APD(90) was little affected. Application of 10(-6)M clentiazem prolonged effective refractory period (ERP) of the A-V node by approximately 7% of the control, an effect similar to that of diltiazem. In spontaneously beating sinoatrial (S-A) node preparations, clentiazem l0(-6)M or the higher concentration significantly decreased APA, V(max), and slope of slow diastolic depolarization, while reducing the maximum diastolic potential. The inhibitory effects of clentiazem showed strong suppression of APA and V(max) by 31.1 and 47.2% of the control, respectively, whereas both clentiazem (10(-7)-10(-5)M) and diltiazem (10(-7)-10(-5)M) had no effects on parameters of ventricular APs. These results suggest that dentiazem, like diltiazem, has a preferential inhibitory action on cardiac slow Ca(2+) channels.

[A case report of multiple pseudoaneurysms of the left ventricle following acute myocardial infarction]

Multiple pseudoaneurysms of the left ventricle following acute myocardial infarction were successfully repaired in a 50-year-old man. Three days after onset of acute myocardial infarction, we electively performed PTCA on the right coronary artery which was completely occluded at the proximal segment. One month after PTCA, the left ventriculogram revealed multiple pseudoaneurysms of the left ventricle. Primary closure of orifices of the pseudoaneurysms was performed using pledgeted mattress sutures under cardiopulmonary bypass. Histology of aneurysm confirmed the diagnosis of pseudoaneurysm.

Diagnosis of right ventricular overload by body surface QRST isointegral maps in children with postoperative right bundle branch block

The utility of body surface QRST isointegral maps (QRST-Imaps) for the detection of right ventricular (RV) overload was examined in children with postoperative development of right bundle branch block. In healthy children with no evidence of bundle branch block (n = 31), the QRST-Imap demonstrated a maximum at the left anterior chest and a minimum near the right shoulder with a single dipole distribution. The positive areas extended from the left anterior chest to the left back, and negative areas extended from the right anterior chest to the right back. Children with complete right bundle branch block but without heart disease demonstrated a QRST-Imap that was similar to that seen in normal children. In patients with RV overload (n = 15; 8 with ventricular septal defect and complicated anomaly and 7 with tetralogy of Fallot), the QRST-Imaps were abnormal and demonstrated double maxima, a rightward shift of the maximum, and extension of positive areas to the right chest. In the 10 patients who developed postoperative complete right bundle branch block, 4 had no evidence of RV overload by hemodynamic or echocardiographic assessment and demonstrated a normal QRST-Imap. In the six children who had residual RV overload during hemodynamic assessment, the QRST-Imap was abnormal. These results suggest that the QRST-Imap is a useful method for the detection of RV overload in pediatric patients complicated with conduction disturbances.

QRST isointegral map reflects the sudden reduction of right ventricular pressure after balloon pulmonary valvuloplasty

To elucidate the mechanism of electrocardiographic changes due to right ventricular pressure overload, serial changes on body surface maps recorded in two children with valvular pulmonary stenosis before and after successful reduction of right ventricular pressure by balloon valvuloplasty (BVP) were studied. Body surface maps and 12-lead electrocardiograms were simultaneously recorded before and 1-1.5 hours, 8 hours, and 5 days after BVP. Before BVP, QRST isointegral maps showed either two maxima or an expanded single maximum on the right anterior chest. These abnormal characteristics become normal or near normal 1-1.5 hours after BVP. Electrocardiographic waveforms and QRS and ST-T isointegral maps showed minimal changes. Changes in QRST isointegral maps were observed near the center of the midanterior chest. These results suggest that increased right ventricular pressure caused a primary repolarization abnormality in the mid-anterior chest that was easily detected by body surface QRST isointegral maps.

Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes

Effects of extracellular magnesium (Mg2+) on action potential duration (APD) and underlying membrane currents in guinea pig ventricular myocytes were studied by using the whole cell patch-clamp method. Increasing external Mg2+ concentration [Mg2+]o) from 0.5 to 3 mM produced a prolongation of APD at 90% repolarization (APD90), whereas 5 and 10 mM Mg2+ shortened it. [Mg2+]o, at 3 mM or higher, suppressed the delayed outward K+ current and the inward rectifier K+ current. Increases in [Mg2+]o depressed the peak amplitude and delayed the decay time course of the Ca2+ current (ICa), the latter effect is probably due to the decrease in Ca(2+)-induced inactivation. Thus 3 mM Mg2+ suppressed the peak ICa but increased the late ICa amplitude at the end of a 200-ms depolarization pulse, whereas 10 mM Mg2+ suppressed both components. Application of 10 mM Mg2+ shifted the voltage-dependent activation and inactivation by approximately 10 mV to more positive voltage due to screening the membrane surface charges. Application of manganese (1-5 mM) also caused dual effects on APD90, similar to those of Mg2+, and suppressed the peak ICa with slowed decay. These results suggest that the dual effects of Mg2+ on APD in guinea pig ventricular myocytes can be, at least in part, explained by its action on ICa with slowed decay time course in addition to suppressive effects on K+ currents.

Role for ATP-sensitive K+ channel in the development of A-V block during hypoxia

The role of the ATP-sensitive K+ channel (IK,ATP) in the development of A-V block during hypoxic interventions was studied using Langendorff perfused rabbit hearts, multicellular rabbit A-V nodal preparations and single guinea-pig ventricular myocytes. With the Langendorff perfused hearts, hypoxic perfusion (PO2 not equal to 40 mmHg) for 30 min caused slowing of the sinus rate and prolongation of the A-H interval without the appearance of blocked beats. Substrate-free hypoxic perfusion induced second or third degree A-V block in 8/10 hearts and substrate-free hypoxic perfusion plus 2-deoxyglucose (5 mM) produced third degree A-V block in 6/6 preparations. Addition of 50 mM glucose in the perfusate restored A-V conduction during hypoxic intervention. Application of glibenclamide, a specific blocker of IK,ATP, prevented the development of second or third degree A-V block during substrate-free hypoxia (n = 6), whereas pinacidil, an opener of IK,ATP, caused development of third degree A-V block during hypoxia (n = 9). Application of theophylline (100 microM) or 8-phenyl-theophylline (10 microM) did not prevent the development of advanced degrees of A-V block during hypoxic interventions. In multicellular A-V nodal preparations, 10 microM glibenclamide prevented the shortening of action potential duration and block development without marked effects on the maximum upstroke velocity of action potentials during hypoxic intervention. In isolated ventricular myocytes studied by the patchclamp method, the substrate-free hypoxia plus 2-deoxyglucose induced the openings of IK,ATP in 9/25 preparations with cell-attached patches, while 2/20 patches exhibited sporadic channel openings in the normoxic condition during comparable observation period. These results suggest that openings of the ATP-sensitive K+ channels play a role in the development and aggravation of advanced A-V block during hypoxic interventions.

Properties of single potassium channels in guinea pig hepatocytes

The patch-clamp technique of cell-attached and inside-out configurations was used to study the single potassium channels in isolated guinea pig hepatocytes. The single potassium channels in isolated guinea pig hepatocytes were recorded at different K+ concentrations. A linear single-channel current-voltage relationship was obtained at the voltage range of -80 to -20 mV with slope conductance of 70 +/- 6 pS (n = 10). Under symmetrical high K+ concentration of 148 mM in the cell-attached patch membrane, the I-V curve exhibited a mild inward rectification at potentials positive to + 20 mV. The values of reversal potential was +5 +/- 2 mV (n = 10). When the external potassium concentration ([K+]o) was decreased to 74 mM and 20 mM, the slope conductance was decreased to 48 +/- 2 pS (n = 4) and 24 +/- 3 pS (n = 3), respectively. The reversal potential was changed by 58 mV for a tenfold change in [K+]o, indicating that this channel was highly selective for K+. Open probabilities (Po) of the channel were 73-93% without apparent voltage dependence. The distributions of open time of the channels were fitted to two exponentials, while those of closed time were fitted to three exponentials, exhibiting no voltage dependence. The success rate of K+ channel activity to be recorded was 28% at room temperature, and there were no increases in the success rate nor in the channel opening probabilities at a temperature of 34-36 degrees C. Po in inside-out patches was not changed by application of 1 microM Ca2+ nor 1 mM Mg2+ to the internal side of patch membranes. It is concluded that a novel type of the K+ channels in guinea pig hepatocytes had different properties of slope conductance, channel kinetics, and sensitivity to [Ca2+]i, from those in other species.

Effects of magnesium on polymorphic ventricular tachycardias induced by aconitine

We examined the effects of Mg2+ on aconitine-induced polymorphic ventricular tachycardias (PVT) in excised rabbit hearts under Langendorff perfusion and in Purkinje-muscle preparations. Local electrograms using bipolar electrodes and transmembrane potentials with the microelectrode technique were recorded from Langendorff hearts and Purkinje-muscle preparations, respectively. In Langendorff preparations, intracoronary application of 0.1 microM aconitine induced PVT 28.8 +/- 3.4 min after development of regular monomorphic ventricular tachycardias (MVT) in all 18 preparations. Application of 5 and 10 mM Mg2+ restored aconitine-induced PVT to sinus rhythm after 26.8 +/- 3.4 min (n = 9), but < 3 mM Mg2+ was not effective in restoring of sinus rhythm. Increased Mg2+ concentrations < or = 5 mM in the coronary perfusate prevented development of PVT by aconitine. Intracoronary application of 10 microM tetrodotoxin (TTX) also restored aconitine-induced PVT to sinus rhythm after 3.2 +/- 0.8 min (n = 4). Although applications of 50 microM lidocaine, 10 microM flecainide, or 1 microM verapamil could change PVT to MVT, they were not effective in restoring sinus rhythm. In Purkinje-muscle preparations, spontaneous action potentials (AP) from slow diastolic depolarization appeared after aconitine at the maximum diastolic potential of -75.0 +/- 3.7 mV in Purkinje fibers and were conducted to ventricular muscles (n = 5). Spontaneous activity gradually increased in rate and then developed triggered activity arising from early after depolarization (EAD). EAD induced by aconitine always appeared first in Purkinje fibers and later in muscle fibers. Once triggered activities started from EAD, rate, rhythm and amplitudes of APs became fast and variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate-dependent effects of sematilide on action potential duration in isolated guinea pig ventricular myocytes

We examined the underlying mechanism for rate-dependent effects of sematilide on action potential duration (APD) in guinea pig ventricular myocytes. Sematilide at 10 microM or higher concentrations caused prolongation of the APD without changing other electrical parameters at a stimulation rate of 0.2 Hz. Although 30 microM sematilide significantly prolonged APD by 20 to 40% at 0.2 Hz, the drug-induced prolongation became non-significant at 2.5 Hz, exhibiting a reverse use-dependent effect. Sematilide depressed the delayed outward K+ current (IK) without affecting the inward rectifier K+ current and the L-type Ca++ current. Suppression of IK by sematilide was more prominent on the tail current elicited by short pulses than on those elicited by long pulses, suggesting that its main action was on the rapidly activating component of IK. Sematilide was shown to have an affinity to the rested state of the IK channel, because the inhibition was increased with prolongation of diastolic intervals at -80 mV. Rapid-rate depolarizations induced a transient outward current that was abolished by 5 mM caffeine. This caffeine-sensitive transient outward current could contribute to the shortening of the APD at rapid pulsation, but sematilide had no effects on this current. Therefore, we conclude that sematilide principally blocked the rapidly activating component of IK with affinity for the rested state of the IK channel and did not block the slowly activating component. Also the drug did not affect the caffeine-sensitive transient outward current during rapid-rate depolarizations. All of these factors may contribute to reverse use-dependent effects on action potential prolongation by sematilide.

Mechanism for reactivation of the ATP-sensitive K+ channel by MgATP complexes in guinea-pig ventricular myocytes

1. A mechanism underlying reactivation of the adenosine 5'-triphosphate-sensitive K+ (K+ATP) channels by MgATP complexes after run-down was examined in guinea-pig ventricular myocytes using the patch-clamp technique with inside-out patch configuration. 2. After run-down was induced by exposure of the intracellular side of the membrane patch to Ca2+ (1 mM), channel activity was reactivated by exposure and subsequent wash-out of MgATP (2 mM). Addition of inhibitors of various serine/threonine protein kinases to the MgATP solution did not suppress reactivation of the run-down channels. 3. Non- or poorly hydrolysable ATP analogues were unable to reactivate run-down channels. 4. The degree of channel recovery was dependent upon the duration of MgATP exposure. The apparent half-activation value (K1/2) of MgATP for reactivation was decreased with increasing exposure time. 5. Various products of ATP hydrolysis were unable to reactivate run-down channels except a relatively low concentration (100 microM) of ADP exposure. 6. Other nucleotide triphosphates, in the presence of Mg2+, were unable to reactivate rundown channels. 7. Fluorescein 5-isothiocyanate (50 microM), which interacts with lysine residues of the nucleotide-binding site on various ATPases, inhibited K+ATP channel activity. After wash-out, channel activity recovered only slightly. 8. These data suggest that the hydrolysis of ATP is important for reactivation of run-down K+ATP channels but that protein phosphorylation by serine/threonine protein kinases may not be involved. Since no products of ATP hydrolysis could reproduce MgATP-induced channel reactivation and since the degree of channel recovery was dependent upon the duration of MgATP application, the hydrolysis energy appears to be utilized for channel reactivation.

Effects of NS-2, a new class 1 antiarrhythmic agent, and AFD-19, its active metabolite, on ventricular arrhythmias induced by coronary artery occlusion and reperfusion in anesthetized rats: comparison with disopyramide and mexiletine

We studied the antiarrhythmic effects of NS-2 (4-diisobutylamino-1,1-diphenyl-1-butanol maleate) and AFD-19 (active metabolite of NS-2) on early stage ventricular arrhythmias induced by coronary artery occlusion and reperfusion in anesthetized male rats. These effects were compared with those of disopyramide and mexiletine. Drugs were intravenously administered either before or after coronary occlusion. When administered 5 min before occlusion, 3 mg/kg of NS-2 and AFD-19 exhibited equivalent anti-arrhythmic activity to that of 5 mg/kg of disopyramide and mexiletine, as assessed by reductions in the number of premature ventricular complexes and in the incidences of ventricular tachycardia and ventricular fibrillation. In a dose of 5 mg/kg, the antiarrhythmic effects of NS-2 and AFD-19 were more pronounced. When administered 5 min after coronary artery occlusion, only NS-2 and AFD-19 (in doses of 5 mg/kg) had significant antiarrhythmic effects. None of the drugs influenced the severe ventricular arrhythmias induced by reperfusion when administered 1 min before reperfusion. In conclusion, NS-2 might be effective in reducing the severity of the life-threatening ventricular arrhythmias that occur during acute myocardial infarction.

External pH modifies sodium channel block by mexiletine in guinea pig ventricular myocytes

OBJECTIVE

The aim was to examine the kinetics and the degree of Na+ channel block by mexiletine under different values of external pH to produce a fractional variation of charged and uncharged forms of mexiletine.

METHODS

The Na+ current (INa) was recorded using the patch clamp technique of whole cell configuration in guinea pig ventricular myocytes.

RESULTS

In the presence of 20 microM mexiletine, INa block developed with a single exponential when depolarising pulse trains of 5 ms were applied to -30 mV from a holding potential of -100 mV at a diastolic interval of 500 ms. At the 30th pulse, the degree of use dependent block of INa was 12.3(SEM 0.41)% (n = 4) of the 1st pulse. When the duration of pulses was prolonged to 200 ms, the degree of use dependent block was increased to 25.6(4.7)%, which had the block development of two exponentials with fast and slow rate constants. The slow component at the 200 ms pulses was comparable to the single exponential component at the 5 ms pulses. Drug binding to the inactivated channel was increased by external alkalinisation, which increased the uncharged form of mexiletine, whereas the block at the 5 ms pulses was not affected by the change of external pH.

CONCLUSIONS

Uncharged mexiletine caused use dependent block with a fast rate constant having affinity for the inactivated state of the Na+ channel, while the charged form produced a slow component of the block having affinity for the activated state. Therefore the fraction of the uncharged to the charged form of mexiletine could be one of the important determinants in the development and mechanism of INa block.

Subcellular mechanism for Ca(2+)-dependent enhancement of delayed rectifier K+ current in isolated membrane patches of guinea pig ventricular myocytes

Intracellular Ca2+ augments delayed rectifier K+ current (IK) in cardiac myocytes, which may play a major modulatory role in repolarization of action potentials. We investigated subcellular mechanisms for Ca(2+)-induced enhancement of IK in large-pipette inside-out membrane patches excised from isolated guinea pig ventricular myocytes. When [Ca2+]i was raised from 10(-8) to 10(-6) mol/L, the amplitude of IK measured at +80 mV was increased from 12.0 +/- 2.2 to 19.5 +/- 3.3 pA (P < .01). The enhancement of IK by Ca2+ was dose dependent, with an EC50 of 3.8 x 10(-8) mol/L. A calmodulin antagonist, W7 (50 mumol/L), calmidazolium (100 mumol/L), or HT-74 (20 mumol/L), added to the intracellular solution abolished enhancement of IK by Ca2+, whereas the inactive form of the W7 analogue, W5, had no effect on IK. In the presence of a protein kinase inhibitor with a relatively high specificity for protein kinase C (H7), for protein kinase A (H8 or peptide-type inhibitor PKI), or for calmodulin kinase II (KN-62) or a nonspecific inhibitor of serine/threonine protein kinases (staurosporine), increases in [Ca2+]i still enhanced IK. Ca(2+)-induced enhancement of IK was also observed when Mg2+ and ATP were omitted from the intracellular solution to delete exogenous phosphate donors and when adenylylimidodiphosphate was added to preclude trapped cytoplasmic substrates. Thus, cardiac IK was enhanced by increases in [Ca2+]i at a physiological range via a calmodulin-dependent pathway, which did not involve a phosphorylation process.

Stilbene disulfonates block ATP-sensitive K+ channels in guinea pig ventricular myocytes

Effects of stilbene disulfonates on single KATP channel currents were investigated in inside-out and outside-out membrane patches from guinea pig ventricular myocytes. All drugs tested, 4,4'-diisothiocyanatostilbene,2,2'-disulfonic acid (DIDS), 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS), and 4,4'-diaminostilbene-2,2'-disulfonic acid (DADS), inhibited the KATP channel when they were applied to the intracellular, but not extracellular side of the membrane patch. Inhibitory actions of DIDS and SITS were irreversible, whereas those induced by DNDS and DADS were reversible. KATP channel inhibition was concentration dependent with an order of potency of DIDS > SITS approximately DNDS > DADS; the Hill coefficient was close to unity for each drug. No change in channel conductance was observed during exposure to DIDS or DNDS; however, channel kinetics was altered. Distribution of the open time within bursts and that between bursts could be described by a single exponential relation in the absence and presence of DIDS or DNDS. The time constant of the open time within bursts was not altered, but that between bursts was decreased by DIDS (from 40.0 +/- 8.1 to 29.8 +/- 6.7 msec, P < 0.05) and by DNDS (from 43.1 +/- 9.3 to 31.9 +/- 7.1 msec, P < 0.05). Distributions of closed time within bursts were also fitted to a single exponential function both in the absence and presence of drugs, while those of the closed time between bursts were fitted to a single exponential function in the absence of drugs, but a double exponential function was required in the presence of drugs. The rates of onset and development of channel inhibition by DIDS and DNDS appeared to be concentration dependent; a longer time was required to reach a new steady-state of channel activity as drug concentration was decreased. Inhibition by DIDS or DNDS was regulated by intracellular pH; inhibition was greater during acidic conditions. For DIDS (0.1 mM), the open probability (Po) expressed as a fraction of the value before drug application was 42.9 +/- 8.3% at pH 7.4 and 8.2 +/- 6.6% at pH 6.5 (P < 0.01); corresponding values for DNDS (1 mM) were 39.6 +/- 17.6 and 8.9 +/- 5.8%, respectively (P < 0.01). From these data, we conclude that stilbene disulfonates block the KATP channel by binding to their target site with one-to-one stoichiometry. Similar to glibenclamide, the binding of stilbene disulfonates may reflect interpolation in an "intermediate lipid compartment" between the cytosolic drug and the site of drug action.

Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes

We studied the effect of cytoplasmic acidosis on the ionic conducting states of ATP-sensitive potassium channels in heart ventricular cells of guinea pigs and rabbits by using a patch-clamp technique with inside-out patch configuration. Under normal conditions (pH 7.4), the channel alternated between a closed state and a main open state in the absence of nucleotides on the cytoplasmic side. As internal pH was reduced below 6.5, the single channel current manifested distinct subconductance levels. The probability of the appearance of these subconductance levels was pH dependent with a greater probability of subconductance states at lower pH. A variance-mean amplitude analysis technique revealed two subconductance levels approximately equally spaced between the main open level and the closed level (63 and 33%). A current-voltage plot of the two subconductance levels and the main level showed that they had similar reversal potentials and rectification properties. An intrinsic flickering gating property characteristic of these ATP-sensitive channels was found unchanged in the 63% subconductance state, suggesting that this subconductance state and the main conductance state share similar ion pore properties (including ion selection and block) and similar gating mechanisms. The appearance of the subconductance states decreased as ionic strength was increased, and the subconductance states were also slightly voltage dependent, suggesting an electrostatic interaction between the protons and the negative surface charge in the vicinity of the binding sites, which may be close to the inner entrance of the ion pore. Proteolytic modification of the channel on the cytoplasmic side with trypsin did not abolish the subconductance levels. External acidosis did not induce subconductance levels. These results suggest that protons bound to the negatively charged group at the inner entrance of the channel ion pore may induce conformational changes, leading to partially reduced conductance states.

Use-dependent block of Na+ currents by mexiletine at the single channel level in guinea-pig ventricular myocytes

1. The mechanism of use-dependent block of Na+ current by mexiletine was studied at the single channel level in guinea-pig ventricular myocytes by the patch-clamp techniques. All experiments were performed using stimulation protocols to enable us to analyze the strict dependence of changes in channel properties on channel use. 2. In cell-attached patches, bath or pipette application of mexiletine (40 microM) produced a use-dependent reduction of the peak average current without changes in single channel conductance. Null sweeps were increased and the number of openings per sweep decreased with successive pulses, whereas no significant change in the mean open time was detected during the train. 3. Block by mexiletine became greater when pulse duration was extended beyond the period in which channels were open, suggesting that block progressed without channel opening. 4. At near threshold potentials, mexiletine decreased the later occurrence of first openings. Additionally, late openings were reduced in a use-dependent way. 5. We conclude that mexiletine binds to the inactivated closed states of the Na+ channel and then causes a failure of late openings as well as early, which results in null sweeps on subsequent depolarization.

Activation and reactivation of the ATP-sensitive K+ channel of the heart can be modified by drugs

Activation and reactivation of the ATP-sensitive K+ channel (IK.ATP) were studied with the patch-clamp technique in guinea-pig ventricular myocytes. The K+ channel openers, nicorandil and pinacidil, activated IK.ATP in an internal ATP-dependent manner. Both drugs increased the open probability of IK.ATP without changing the channel conductance. They prolonged lifetimes of bursts and shortened interburst intervals without influencing the fast gating within bursts. These effects were the opposite of those of internal ATP. However, the interaction between ATP and either nicorandil or pinacidil appeared not to be simple competition. We found that three carbonyl compounds--3,4-dihydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde, and 2,4-dihydroxyacetophenone--could activate IK.ATP through an intracellular mechanism that was dependent upon the presence of ADP and Mg2+. It has been suggested that these three carbonyl compounds bind covalently to proteins to form a Schiff base, which may be responsible for their effects upon IK.ATP. Internal application of the proteolytic enzyme trypsin prevented both the spontaneous and Ca(2+)-induced rundown of the KK.ATP channel. Tryptic digestion did not change either the channel's sensitivity to inhibition by ATP nor the fast gating kinetics of IK.ATP. Internal application of an exopeptidase, carboxypeptidase A, but not leu-aminopeptidase, prevented the spontaneous and Ca(2+)-induced rundown of the IK/ATP channel, effects similar to those of trypsin treatment. These results suggest that the target site of trypsin digestion may be located on the carboxy (C)-terminal of the channel proteins or associated regulatory units.

Modification of the adenosine 5'-triphosphate-sensitive K+ channel by trypsin in guinea-pig ventricular myocytes

1. The adenosine 5'-triphosphate (ATP)-sensitive K+ channel current was recorded in guinea-pig ventricular myocytes using the patch clamp technique with inside-out patch configuration. Modification of the channel activity by intracellular application of an endoprotease trypsin was studied, and was related to a possible model of regulation of this channel. 2. Maximal ATP-sensitive K+ channel activity was observed immediately upon formation of inside-out patches in the ATP-free internal solution, thereafter activity declined both spontaneously and gradually with time; a phenomenon known as rundown. When trypsin (1 mg/ml) was applied to the intracellular side of the membrane upon formation of inside-out patches, spontaneous run-down did not occur, and this trypsin action was irreversible. Neither trypsin (1 mg/ml) applied with trypsin inhibitor (0.25 mg/ml) nor heat-denatured trypsin (1 mg/ml) could mimic this effect. When trypsin was applied to the patches after run-down, channels were reactivated at approximately 13 min. 3. Treatment with trypsin did not affect unitary current amplitude, channel gating kinetics, or sensitivity to intracellular ATP. 4. Intracellularly applied Ca2+ induced run-down of channel activity in a dose-dependent manner. In membrane patches that were treated with trypsin (1 mg/ml) for 20 min, intracellularly applied Ca2+ up to 1 mM did not induce run-down of channel activity. 5. Intracellular application of an exopeptidase, carboxypeptidase A (1 mg/ml), but not Leu-aminopeptidase (0.5 mg/ml), prevented spontaneous or Ca(2+)-induced run-down of channel activity. 6. As postulated for several other channels, such as Na+ and Ca2+ channels, there may be a possible 'chemical gate' that is responsible for run-down of this channel activity. Application of trypsin might somehow modify this 'chemical gate', resulting in prevention of spontaneous or Ca(2+)-induced run-down. This target site for trypsin may be situated on the carboxy-terminus of the channel proteins, or of associated regulatory units. Because ATP sensitivity remained intact after trypsin treatment, the trypsin-selective site for channel inhibition is not related physically to the ATP binding site.

Use-dependent block of Ca2+ current by moricizine in guinea-pig ventricular myocytes: a possible ionic mechanism of action potential shortening

1. Whole cell patch clamp techniques were used to study the effects of moricizine on membrane currents in guinea-pig ventricular myocytes. 2. Application of moricizine caused reversible depression of the time-dependent outward K+ current. 3. The Na+/Ca2+ exchange current was not directly affected by moricizine. 4. Although moricizine hardly affected the L-type Ca2+ current when cells were stimulated at a frequency of 0.1 Hz, it suppressed the current at depolarized holding potentials in a use-dependent manner at 1 Hz. 5. Developments of use-dependent block of the Ca2+ current in the presence of moricizine were best expressed by two exponentials. Binding to both activated and inactivated states of the Ca2+ channel were supported from the binding kinetics study. 6. We concluded that moricizine suppressed the L-type Ca2+ current in a use-dependent manner and this might explain, at least in part, action potential shortening by the drug.

[Risk factors for contrast nephropathy in diabetic patients undergoing cardioangiography]

Risk factors for contrast nephropathy were prospectively studied in 17 patients with non-insulin dependent diabetes mellitus undergoing cardioangiography. Contrast nephropathy, defined as a serum creatinine increase of greater than 25% at 3 day after angiography, occurred in 29.4% of diabetic patients. Patients who developed contrast nephropathy had significantly higher serum creatinine (Cr), fractional excretion of sodium (FENa), urinary albumin excretion rate (AER), and lower 24hr Ccr than patients who did not (Cr: 1.5 +/- 0.3 mg/dl vs. 0.8 +/- 0.1 mg/dl, FENa: 1.9 +/- 0.5% vs. 0.6 +/- 0.1%, AER: 522 +/- 335 micrograms/min vs. 27 +/- 13 micrograms/min, 24hr Ccr: 39.1 +/- 11.6 ml/min vs. 86.2 +/- 9.3 ml/min, P < 0.05). Contrast nephropathy developed in all of two patients with overt proteinuria (AER more than 200 micrograms/min), but none of eight patients with normoalbuminuria (AER below 15 micrograms/min). Three of seven patients with microalbuminuria developed contrast nephropathy, and two of them had advanced nephropathy. FENa obtained next day was significantly elevated over baseline in patients with contrast nephropathy (1.9 +/- 0.5% vs. 9.7 +/- 4.5%, P < 0.05), but unchanged in patients without contrast nephropathy. The rise in C beta 2-microglobulin/Ccr and enzymuria was noted in both group. Percentage decrease of Ccr on the next day was positively correlated with FENa before angiography (r = 0.645, p < 0.01). Of 24hr Ccr, AER, and FENa before angiography, FENa was revealed as a statistically significant discriminant factor for contrast nephropathy by stepwise discriminant analysis (p = 0.0008). These results suggest that contrast nephropathy develops predominantly in the stage not of incipient but of overt diabetic nephropathy indicated by a decline of glomerular filtration, overt proteinuria, and tubular dysfunction. Of them, tubular dysfunction may be the most important risk factor for contrast nephropathy.

The body surface QRST isointegral maps in infants with right ventricular overload

Electrocardiographic criteria for right ventricular (RV) hypertrophy in infants generally exhibit low sensitivity in terms of diagnostic accuracy. We studied the QRST isointegral map (QRST-Imap) of body surface potential distribution for the diagnosis of RV overload in patients less than 2 years old. Patients with atrial septal defect (ASD), pulmonary stenosis (PS) and tetralogy of Fallot (TOF) were examined (RV overload group) and the findings of their QRST-Imaps were compared to those of age-matched healthy infants (NOR). QRST-Imaps in RV overload showed abnormal findings, with two maxima or a rightward shift of the maximum with increased amplitude, in contrast to one maximum at the left anterior chest with a single dipole pattern in the NOR group. ASD patients had two maxima with a decreased integral value between them. In PS, two maxima were also observed, with increased integral values of the right maximum as the RV systolic pressure was elevated. TOF patients showed a single maximum shifted to the anterior median line with increased amplitude. These results indicate that the findings of QRST-Imaps are of value in detecting the presence and pattern of RV overload in infants.

Endothelin-1 enhances calcium entry through T-type calcium channels in cultured neonatal rat ventricular myocytes

Endothelin-1 (ET-1), a 21-amino acid vasoconstrictive peptide, increases intracellular Ca2+ level and has hypertrophic action on ventricular myocytes. To elucidate a possible role of Ca2+ entry through sarcolemmal Ca2+ channels on this ET-1 action, we examined effects of ET-1 on L-type (ICa,L) and T-type (ICa,T) Ca2+ currents in cultured neonatal rat ventricular myocytes using the patch-clamp technique. ET-1 at a concentration of 10 nM increased the maximum current density of ICa,T from -3.0 +/- 1.4 microA/cm2 in the control condition to -4.4 +/- 1.6 microA/cm2 (p < 0.01). Although the peak amplitude of ICa,L was decreased during ET-1 application (from -9.7 +/- 1.9 microA/cm2 in the control condition to -5.0 +/- 1.4 microA/cm2 [p < 0.01]), this magnitude of decrease in ICa,T (52 +/- 19%) was comparable to that of spontaneous "run-down" of ICa,L (47 +/- 26%). The enhancement of ICa,T by ET-1 was dose dependent; it was initiated as low as 0.32 nM, and the maximal response was attained at approximately 10 nM, with a half-maximal dose of 1.26 nM. The enhancement of ICa,T by ET-1 was antagonized by protein kinase C inhibitors staurosporine (0.2 microM) and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7, 20 microM) applied to the pipette solution. Extracellular application of tumor-promoting phorbol esters, phorbol 12,13-dibutyrate (PDBu) and 4 beta-phorbol 12-myristate 13-acetate, augmented ICa,T. PDBu (0.2 microM) increased the maximal current density of ICa,T from -4.2 +/- 0.5 microA/cm2 in the control condition to -5.5 +/- 1.0 microA/cm2 (p < 0.01). In the presence of H-7 (20 microM) in the pipette solution, PDBu failed to enhance ICa,T, and an inactive isomer of PDBu (4 alpha-phorbol 12,13-dibutyrate, 0.2 microM) did not augment ICa,T. Thus, ET-1 enhances Ca2+ entry through the sarcolemmal T-type Ca2+ channel, possibly through a pathway involving activation of protein kinase C. This ET-1 action may be involved in the rise of the intracellular Ca2+ level and may contribute to the induction of cardiac hypertrophy by ET-1.

Arrhythmogenic effects of isoproterenol-activated Cl- current in guinea-pig ventricular myocytes

Possible arrhythmogenic effects of the isoproterenol-activated Cl- current were examined in isolated guinea-pig ventricular myocytes under various intra- and extracellular Cl- concentrations. Experiments were carried out with external K+ concentration ([K+]o) decreased to 2 or 3 mM. Under symmetrical concentrations of Cl- in intra- and extra-cellular solutions (ECl = 0 mV), 1 microM isoproterenol (ISP) depolarized resting membrane potential (RMP) by 6.2 +/- 1.1 mV and slowed repolarization with induction of early afterdepolarizations (EADs) in 9 out of 9 cells. EADs appeared at voltages positive to -40 mV, where L-type Ca2+ current is assumed to be activated. When Cl- concentrations were settled near physiological conditions (ECl = -40 - -50 mV), ISP depolarized RMP by 2.8 +/- 0.4 mV and elicited abnormal repolarization with occasional EADs in 6 out of 19 cells. When ECl was set to -80 mV, however, ISP depolarized RMP by only 0.5 +/- 0.5 mV without induction of abnormal activities. Thus, depolarizing effects of ISP and incidence of repolarization abnormalities including EADs were increased as ECl shifted to more positive potential levels. At [K+]o = 4 mM, no abnormal activities were observed when ECl was around -50 mV (0/8), and 6 out of 6 cells showed abnormal activities when ECl was set to 0 mV. ISP-elicited abnormal activities were abolished by 1 mM DNDS (4,4'-dinitrostilbene-2,2'-disulphonic acid), a blocker for Cl- channels.(ABSTRACT TRUNCATED AT 250 WORDS)