Ductus venosus blood flow assessment at 11 to 14 weeks of gestation and fetal outcome.

OBJECTIVE: To evaluate the association between abnormal ductus venosus (DV) at 11-14 weeks' gestation and chromosomal abnormalities, structural defects and fetal outcome. METHODS: DV flow-velocity waveform (DV-FVW) and nuchal translucency thickness (NT) were prospectively evaluated in 1217 singleton pregnancies. RESULTS: The DV-FVW was abnormal in 84 fetuses, NT was above the 95th centile in 160 fetuses and both markers were observed in 41 fetuses. Chromosomal defects were diagnosed in 22 fetuses. The sensitivity, specificity and positive and negative predictive values for an abnormal karyotype were 86.4%, 86.9%, 11.9% and 99.7%, respectively, for an increased NT. These values were 68.2%, 96.9%, 31.3% and 99.3%, respectively, for DV-FVW abnormalities and 68.2%, 97.6%, 36.6% and 99.3%, respectively, when both markers were found simultaneously. Regarding structural defects, these values were 43.8%, 92.9%, 8.3% and 99.1% for an abnormal NT, 25.0%, 92.6%, 4.8% and 98.8% for DV-FVW abnormalities and 25.0%, 97.9%, 15.4% and 98.9% for both together. Considering those cases of unexplained fetal demise, the values were 44.4%, 85.9%, 5.0% and 98.9% for NT abnormalities, 22.2%, 92.6%, 4.8% and 98.6% for an abnormal DV-FVW and 22.2%, 98%, 15.4% and 98.7% for both. In cases with increased NT, the percentage of live births with normal karyotype and no major fetal structural defects decreased from 93.8% in normal DV-FVW fetuses to 77.3% in abnormal ones. CONCLUSION: DV assessment at 11-14 weeks' gestation is useful in screening for fetal chromosomal abnormalities and may help to reduce the false-positive rate when combined with NT measurement. Abnormal DV-FVW is also associated with an increase in adverse perinatal outcome in fetuses with enlarged NT. However, the value of DV-FVW assessment in cases with normal NT is unclear.

Angiographic classification of coronary dissections after plain old balloon angioplasty for prediction of regression at follow-up.

Coronary dissection after plain old balloon angioplasty often shows regression during follow-up. This study sought to determine whether we can predict such phenomenon angiographically. We analyzed 64 patients with 71 type B-D coronary dissections determined by the National, Heart, Lung, and Blood Institute (NHLBI) criteria. Regression was considered present when minimal lumen diameter increased by more than 0.3 mm during follow-up. Dissections were divided into subgroups using the NHLBI criteria and our classification in which type a and b dissections were characterized by the width of a dissection lumen exceeding one quarter of the reference diameter with the outer edge of the dissection lumen within the boundary of reference in type a and beyond it in type b. In type c and type d dissections, the width of the dissection lumen was within one quarter of the reference with its outer edge within the boundary of reference in type c and beyond it in type d. Type e dissection had a protruding flap or spiral appearance. Regression was recognized in 23.9%. The distribution of dissection types was similar in the groups with and without regression by the NHLBI criteria, but type c dissection had regression more frequently than the other types of coronary dissections (p<0.001) using our classification.

Risk factors for sudden unexpected death among workers: a nested case-control study in central Japan.

UNLABELLED: BACKGROUND; Few studies have focused on sudden death among apparently healthy workers, and the risk factors have not been fully discussed. METHODS: A nested case-control study was conducted among 164,017 male employees receiving annual medical checkups in Japan. Most recent medical checkup data of 242 sudden death victims (mean age, 48.0 years) were compared with corresponding data of 505 age-, workplace-, and job-type-matched male controls. Odds ratios (ORs) and their 95% confidence intervals (CIs) for each variable were calculated by logistic regression. RESULTS: OR (95% CI) significantly increased with advancing blood pressure, reaching 6.6 (3.4-13.1) for systolic blood pressure > or =160 mm Hg relative to that <120 mm Hg. Hypo-HDL-cholesterolemia, hyperuricemia, increased aminotransferases, and abnormal urinary findings were associated with the risk in a dose-dependent manner. The presence of arrhythmias and ST-T abnormalities as well as abnormal Q waves on electrocardiograms yielded a 3.5 to 4.8 times greater risk of sudden death. As for lifestyles, heavy smoking was a positive, and light drinking was a negative risk factor. Multivariate analysis revealed that hypertension, proteinuria, glucosuria, arrhythmias, ST-T abnormalities, and light drinking were independent predictors for sudden death. CONCLUSION: These findings suggest that periodic medical checkups can help to predict and prevent employee sudden death.

Three-year follow-up of patients with right bundle branch block and ST segment elevation in the right precordial leads: Japanese Registry of Brugada Syndrome. Idiopathic Ventricular Fibrillation Investigators.

OBJECTIVES: We sought to determine the prevalence of right bundle branch block (RBBB) and ST segment elevation in the working Japanese population, as well as the event rate during a three-year prospective follow-up period. BACKGROUND: A poor prognosis of RBBB and ST segment elevation has been reported in Europe and South America, even in asymptomatic patients; however, a large population of asymptomatic patients with sporadic RBBB and ST segment elevation has not been studied. METHODS: Ten thousand 12-lead electrocardiograms (ECGs) were obtained during annual check-ups of working adults in the Tokyo area. This three-year prospective follow-up study consisted of 105 patients, including 20 with ventricular fibrillation, 18 with syncope and 67 who were asymptomatic. They were registered from 46 institutions in Japan. RESULTS: The prevalence of ECG abnormalities in working adults was 0.16%. A coved-type ST segment elevation was related to a history of cardiac events, and 18% of registered patients had PR prolongation and 9.5% had left-axis deviation. The cumulative cardiac event-free rate was 67.6% in the symptomatic group and 93.4% in the asymptomatic group (p = 0.0004) after three years. CONCLUSIONS: The recurrence rate of cardiac events in symptomatic patients was similar to that reported previously, but it was very low in sporadic asymptomatic patients. The ECG findings may help us to select patients for further examination and more accurate evaluation of their prognoses.

[13C-urea breath test].

A 13C-urea breath test(13C-UBT) is known to be a good diagnostic method for detecting H. pylori infection since it is non-invasive, simple and accurate. Its diagnostic capability in determining H. pylori eradication has been studied using 153 patients (who underwent the H. pylori eradication therapy) as subjects at two times: 6-8 weeks after the end of administration (at the time of determination of eradication) and 6 months afterwards. When determination was made, the sensitivity and specificity of 13C-UBT compared to culture and histology were 100% and 95.1%, respectively. Seven inconsistent cases were positive according to 13C-UBT and negative according to two other methods. After 6 months, both sensitivity and specificity were 100% and 4 of the 7 inconsistent cases became positive according to all three methods. These results indicate that the 13C-UBT is superior in terms of sensitivity and specificity to culture and histology and recognize the failure eradication earlier than ether two methods. Re-examination of inconsistent cases should be performed after 6 months. After covered by insurance, the H. pylori eradication therapy will become a general form of treatment of peptic ulcers. 13C-UBT in particular has proven most useful for diagnosis of eradication.

Different expressivity of a ventricular essential myosin light chain gene Ala57Gly mutation in familial hypertrophic cardiomyopathy.

BACKGROUND: Familial hypertrophic cardiomyopathy (HCM) is a clinically and genetically heterogeneous disease of the sarcomere. Molecular genetic studies have shown that familial HCM involves mutations in 8 different genes that encode proteins of the myofibrillar apparatus. METHODS: We thoroughly searched these genes to find the mutations in 38 probands of unrelated families with familial HCM. RESULTS: We found a novel missense mutation that resulted in Ala57Gly amino acid substitution of the ventricular essential myosin light chain (vMLC1) gene in two unrelated Korean families with familial HCM and one Japanese patient. The mutated site is located in the putative helix-loop-helix region (named EF-hand domain) of the calcium-binding site that is highly conserved in vMLC1 isoforms across the various species. The phenotype of this mutation in the affected families is a classic asymmetric septal hypertrophy, and the disease penetrance in genotyped members older than 18 years is 78%. In one Korean family a 42-year-old woman and two brothers (34 and 38 years old) with the mutation had fully expressed the disease, but two sisters (39 and 29 years old) with the mutation had no phenotypic expression of HCM. CONCLUSIONS: Ala57Gly mutation in the vMLC1 gene may exhibit the classic form of familial HCM and widely different penetration of the disease phenotype in the family members with mutation, especially in women.

Takayasu arteritis with multiple cardiovascular complications.

A 60-year-old Japanese woman first presented in 1990 with effort angina. She underwent coronary angiography and was diagnosed with bilateral coronary ostial stenosis and Takayasu arteritis. Coronary artery bypass graft surgery (CABG) for multiple vessels was attempted, but the blood flow in the bilateral internal thoracic and gastroepiploic arteries was to poor for a donor artery, and the calcification of the ascending aortic wall was too severe for anastomosis of saphenous vein grafts. Therefore, the proper hepatic artery was connected to the left anterior descending artery using a vein graft. In April 2000, the patient's angina worsened. Occlusions of both subclavian arteries, bilateral coronary ostial stenosis and vein graft occlusion, aortic valve regurgitation, and two severe stenoses of the descending aorta were observed. Aortic valve replacement, and coronary and aorta revascularization were desirable, but the severe aortic wall calcification and thickening rendered these interventions impossible. Treatment with medication was chosen. The patient was discharged without severe angina. A combination of these serious cardiovascular complications which do not allow any surgical intervention is very rare.

[A patient with dermatomyositis and systemic sclerosis with preferential facioscapulohumeral muscle involvement and fatal cardiomyopathy].

We report a 23-year-old man suffering from an overlap syndrome of systemic scleroderma and dermatomyositis who died from severe dilated cardiomyopathy. Because his weakness involved predominantly muscles in the facio-scapulo-humeral regions, he was initially thought to have facioscapulohumeral muscular dystrophy (FSHD) at other hospitals. However, he had also Raynaud phenomenon and low voltages on electrocardiogram. His apparent facial weakness was mainly due to atrophic skin changes. Unlike FSHD, the deltoid and levator scapulae muscles were also atrophic. Deltoid muscle biopsy performed one year earlier at another hospital showed mild myopathic changes without inflammation, but there were scattered thick-walled endomysial capillaries, suggesting inflammatory myopathy. Biceps brachii muscle biopsy in our hospital showed marked inflammation with perifascicular atrophy. In this patient, the cardiac muscle involvement progressed together with the skeletal muscle inflammation before scleroderma became apparent.

Cell-to-cell interaction prevents cell death in cultured neonatal rat ventricular myocytes.

OBJECTIVES: Loss of cardiac cells and the anatomical or functional remodeling of intercellular coupling occur under several pathological conditions. We have assessed the significance of intercellular coupling for cell death. METHODS AND RESULTS: Ventricular cells obtained from 1 day old Wistar rats were cultured. Apoptosis was detected by nick-end labeling. Cells were plated at low and high cell density (3x10(4)/ml and 12x10(4)/ml, respectively). Cultured myocytes died spontaneously by apoptosis in a time dependent manner. The increase of the apoptotic cell population in a culture with high cell density on day 4 (1+/-1.2%, n=4) was significantly lower than that in a culture with low cell density (20+/-5.5%, n=4). The progression of apoptosis in the culture of low cell density was prevented in part after application of the medium extract from the culture of high cell density; the apoptotic cell population on day 6 decreased from 57+/-8.0% (n=4) to 36+/-3.8% (n=4). Treatment of the cultured myocytes at high cell density with antisense oligonucleotide for connexin43 (Cx43) for 24 h on day 2 resulted in a significant decrease in Cx43 expression as judged by Western blot, dye transfer and immunocytochemistry using mouse monoclonal antibody for Cx43. In association with the down-regulation of Cx43, the progress of apoptosis was accelerated; the apoptotic cell population on day 5 in the antisense-treated cultures (27+/-5.7%, n=4) was significantly higher than the sense-treated cultures (5+/-1.1%, n=4). The effect of Cx43 antisense treatment to promote apoptosis was not reversed by application of high cell-density culture medium. CONCLUSIONS: These findings suggest that cell-cell communication through gap junction formation and some humoral factors play important roles in the survival of cultured myocytes.

[Beneficial effect of eyelid make-up (natural rubber latex) to induce a new fold in the treatment of blepharoptosis in myotonic dystrophy].

Blepharoptosis is one of the troublesome ocular complications of myotonic dystrophy. To correct drooping eyelids for two men with myotonic dystrophy, we used Eye Putti, a cosmetic made of natural rubber latex, which induces a new fold in the upper eyelid. The cosmetic rubber latex dramatically improved the sight of a 59-year-old patient who previously had a great difficulty in looking forward and had to bend his head backward to see an object because of severe blepharoptosis. The other patient aged 54 with moderate ptosis also had satisfactory improvement. Appropriate use did not prevent eye blinking and induce corneal erosion or skin rash. The cosmetic rubber latex was effective to patients who had no residual function of the levator palpebrae and frontal muscles. This daily treatment is simple and safe, therefore may have an advantage over surgical correction of blepharoptosis for patients not only with myotonic dystrophy, but with other neuromuscular disorders including oculopharyngeal muscular dystrophy.

Beneficial application of quantitative coronary angiography (edge detection algorithm) in analysis of dissected coronary arteries to predict long-term patency.

The present study evaluated the application of quantitative coronary angiography (edge detection algorithm) for the analysis of coronary dissection lesions after balloon angioplasty. Acute and late results were obtained by the edge detection algorithm in 60 patients with 66 dissected lesions (NHLBI types B-C). The edge detection algorithm delineated the border of the true lumen in 32 lesions (group with automated analysis alone, 48.5%) and included the dissection cap in the analysis in 34 lesions in which manual editing was adjuncted (group with manual editing, 51.5%). In both groups, the minimal lumen diameter after balloon angioplasty obtained by initial automated analysis was correlated to that obtained at the 5.3-month follow-up similarly (r=0.554, p=0.0010 for the group with automated analysis alone and r=0.613, p=0.0001 after automated analysis for the group with manual editing). However, additional manual editing reduced the correlation coefficient (r=0.240, p=0.1707) in the latter group. Thus, in terms of predicting long-term patency, it is reasonable to let the edge detection algorithm decide the measurements in types B and C dissected lesions.

High fever, renal failure, disseminated intravascular coagulation and myelodysplasia accompanied with enhanced angiogenesis possibly due to overexpression of vascular endothelial growth factor.

A 44-year-old woman suffered from recurrent fever, edema and fatigue. Laboratory data revealed renal dysfunction, low proteinemia, disseminated intravascular coagulation (DIC) and myelodysplasia. A renal and lymph node biopsy showed a marked angiogenesis. Serum levels of vascular endothelial growth factor (VEGF), and interleukin (IL)-6 were markedly increased, suggesting a pathogenesis related to VEGF-induced angiogenesis. The symptoms were remitted after treatment with cyclosporin A. No evidence of solid tumors, malignant lymphoma, Castleman's disease or POEMS (polyneuropathy, organomegaly, endocrine disorder, M-proteinemia and skin change) syndrome, reported to induce a high serum VEGF level, was obtained. This case may have involved an unknown mechanism which induced an overexpression of VEGF and IL-6.

Voltage-gated K(+)Channel, Kv4.2, localizes predominantly to the transverse-axial tubular system of the rat myocyte.

Kv4.2 subunit, a member of K(+)channel gene family, is considered to play a major role in the formation of depolarization-activated transient outward K(+)current channels in the mammalian heart. We investigated the subcellular localization of Kv4.2 subunit in the rat heart by immunofluorescence and immunoelectron microscopy. In atrial cells, Kv4.2 immunofluorescent staining was intensely observed in the peripheral sarcolemma and the intercalated disks, but seldom found in transverse tubules, which are rare or absent in atrial cells. In ventricular cells, the labeling of Kv4.2 immunofluorescent staining was found throughout the entire cell membrane, and the staining was stronger in the transverse-axial tubular system than in the peripheral sarcolemma. Correlative immunoconfocal and immunoelectron microscopy using FluoroNanogold confirmed that Kv4.2 distributed in the transverse-axial tubular system including the longitudinally oriented axial tubules. Immunogold electron microscopy of ultrathin cryosections revealed that Kv4.2 was distributed on the plasma membranes of the T-tubules. The extensive distribution of Kv4.2 on the entire cell membrane of myocytes would provide rat myocardial cells with a large capability for the transport of K(+)ions through the channels in the repolarization phase.

Oozing type cardiac rupture repaired with percutaneous injection of fibrin-glue into the pericardial space: case report.

Two patients, a 56-year-old man and an 81-year-old woman who were admitted to hospital because of anteroseptal acute myocardial infarction, were initially treated successfully with direct percutaneous transluminal coronary angioplasty. However, both patients later developed sudden cardiogenic shock due to cardiac tamponade caused by left ventricular free wall rupture (LVFWR). Prompt, life-saving pericardiocentesis was performed, then fibrin-glue was percutaneously injected into the pericardial space. After the procedure, there was no detectable pericardial effusion on echocardiography and the hemodynamic state became stable. The surgical treatment was the standard procedure for LVFWR, but percutaneous fibrin-glue therapy can also be considered for oozing type LVFWR.

Antiarrhythmic efficacy of dipyridamole in treatment of reperfusion arrhythmias : evidence for cAMP-mediated triggered activity as a mechanism responsible for reperfusion arrhythmias.

BACKGROUND: Intracellular calcium overload is believed to play an important role in development of reperfusion arrhythmias. Dipyridamole, an inhibitor of cellular uptake of adenosine, may prevent or terminate reperfusion arrhythmias by reducing intracellular calcium overload. METHODS AND RESULTS: First, we tested for a preventive effect of dipyridamole. Sixty-one patients who underwent primary PTCA for treatment of acute anterior wall myocardial infarction were enrolled in this prospective study. Patients were divided into dipyridamole (DP) and nondipyridamole (non-DP) groups. The 2 groups had similar baseline characteristics. In the DP group, dipyridamole 0.5 mg/kg was infused intravenously for 3 minutes immediately before reperfusion during primary PTCA. Arrhythmias after reperfusion were analyzed from continuous ECG recordings. None of the patients in the DP group (n=23) had accelerated idioventricular rhythms (AIVR) or ventricular tachycardia (VT). In contrast, 7 (18.4%) had AIVR and 3 (7.9%) had VT in the non-DP group (n=38; P<0.01). Second, we tested for a termination effect of dipyridamole. Dipyridamole 0.5 mg/kg was infused intravenously while continuous ECG recordings were obtained in 9 patients who had either sustained AIVR (n=7) or sustained VT (n=2) after reperfusion of occluded coronary artery. Arrhythmias were terminated in all patients. CONCLUSIONS: These results indicate that administration of dipyridamole can prevent and terminate reperfusion arrhythmias such as AIVR and VT. cAMP-mediated triggered activity may, at least in part, be responsible for reperfusion-induced AIVR and VT.

Adriamycin causes dual inotropic effects through complex modulation of myocardial Ca2+ handling.

Effects of adriamycin (ADR) on the twitch contraction of isolated guinea pig cardiac muscles were examined to elucidate its actions on intracellular Ca2+ mobilization. In right ventricular papillary muscles, ADR (100-300 micromol/L) caused positive inotropy when the muscles were constantly stimulated at low frequencies (0.1-0.5 Hz), whereas it caused negative inotropy when the muscles were stimulated at higher frequencies (2.0-3.0 Hz). Action potential duration was prolonged significantly by ADR, especially at the lower frequencies. The potentiation of twitch contraction of the first beat (B 1) following a short rest period (2-10 s) in ventricular muscles was inhibited by ADR. In untreated papillary muscles, B1 contraction showed time-dependent decay in response to a prolongation of the preceding rest period up to 120 s. ADR (300 micromol/L) caused ryanodin-like acceleration for the early B1 decay with rest period less than 20 s, but a substantial deceleration for the later B1 decay (> or =30 s). In left atrial muscles stimulated constantly, ADR had significant negative inotropy throughout the entire range of stimulation frequencies tested (0.1-4.0 Hz). The post-rest potentiation of B 1 contraction of atrial muscle in the presence of nifedipine was also inhibited by ADR. These findings suggest that ADR has dual inotropic effects through a complex modulation of myocardial Ca2+ handling, which may involve (1) an increase of Ca2+ influx through a prolongation of action potential duration, (2) ryanodine-like inhibition of Ca2+ release from the sarcoplasmic reticulum, and (3) inhibition of sarcolemmal Ca2+ extrusion probably through the Na+/Ca2+ exchange.

Downregulation of voltage-gated K(+) channels in rat heart with right ventricular hypertrophy.

The effects of myocardial hypertrophy on mRNA expression levels of voltage-gated K(+) channels were investigated using monocrotaline (MCT)-induced pulmonary hypertensive rats. The ratio of right ventricle weight to left ventricle plus septum weight on day 28 was increased significantly compared with control rats [control vs. MCT: 0.27 +/- 0.01 vs. 0.58 +/- 0.03 ms (n = 8-13); P < 0.05]. Electrocardiograms showed that QRS duration [control vs. MCT: 26.4 +/- 2.6 ms vs. 31.5 +/- 5.8 ms (n = 6); P < 0.05], Q-T interval [control vs. MCT: 100.8 +/- 8.9 ms vs. 110.0 +/- 4.2 ms (n = 6); P < 0.05] and corrected Q-T interval [Q-T(c); control vs. MCT: 8.4 +/- 0. 7 ms vs. 10.2 +/- 0.4 ms (n = 6); P < 0.05] were prolonged significantly on day 28. mRNA levels of Kv1.2, 1.5, 2.1, 4.2, and 4. 3 for day 28 assessed by ribonuclease protection assays were decreased significantly from control by 60 +/- 10, 76 +/- 3, 58 +/- 5, 81 +/- 5, and 45 +/- 12%, respectively (n = 3; P < 0.005), and Kv1.4 mRNA level for day 28 was unaffected [Kv1.4, control vs. MCT: 1.0 +/- 0.28 vs. 0.88 +/- 0.44 (arbitrary units) (n = 3); not significant (NS)]. On the other hand, there was no significant difference between control and MCT rats in mRNA levels of these Kv channels for day 14 [Kv1.2 (control vs. MCT): 1.0 +/- 0.25 vs. 0.87 +/- 0.18 (n = 3), NS; Kv1.4: 1.0 +/- 0.22 vs. 1.27 +/- 0.37 (n = 3), NS; Kv1.5: 1.0 +/- 0.16 vs. 0.91 +/- 0.28 (n = 3), NS; Kv2.1: 1.0 +/- 0.26 vs. 0.99 +/- 0.25 (n = 3), NS; Kv4.2: 1.0 +/- 0.15 vs. 1.22 +/- 0.28 (n = 3), NS; Kv4.3: 1.0 +/- 0.20 vs. 1.21 +/- 0.28 (n = 3), NS]. These findings suggest that altered ventricular repolarization at the advanced stage of hypertrophy may be the result of an inhibition of gene expression of multiple types of voltage-gated K(+) channels.

Amiodarone: ionic and cellular mechanisms of action of the most promising class III agent.

Amiodarone is the most promising drug in the treatment of life-threatening ventricular tachyarrhythmias in patients with significant structural heart disease. The pharmacologic profile of amiodarone is complex and much remains to be clarified about its short- and long-term actions on multiple molecular targets. This article reviews electrophysiologic effects of amiodarone based on previous reports and our own experiments in single cells and multicellular tissue preparations of mammalian hearts. As acute effects, amiodarone inhibits both inward and outward currents. The inhibition of inward sodium and calcium currents (I(Na), I(Ca)) is enhanced in a use- and voltage-dependent manner, resulting in suppression of excitability and conductivity of cardiac tissues especially when stimulated at higher frequencies and in those with less-negative membrane potential. Both voltage- and ligand-gated potassium channel currents (I(K), I(K,Na), I(K,ACh)) are also inhibited at therapeutic levels of drug concentrations. Acutely-administered amiodarone has no consistent effect on the action potential duration (APD). The major and consistent long-term effect of the drug is a moderate APD prolongation with minimal frequency dependence. This prolongation is most likely due to a decrease in the current density of I(K) and I(to). Chronic amiodarone was shown to cause a down-regulation of Kv1.5 messenger ribonucleic acid (mRNA) in rat hearts, suggesting a drug-induced modulation of potassium-channel gene expression. Tissue accumulation of amiodarone and its active metabolite (desethylamiodarone) may modulate the chronic effects, causing variable suppression of excitability and conductivity of the heart through the direct effects of the compounds retained at the sites of action. Amiodarone and desethylamiodarone could antagonize triiodothyronine (T3) action on the heart at cellular or subcellular levels, leading to phenotypic resemblance of long-term amiodarone treatment and hypothyroidism.

Heterogeneous distribution of the two components of delayed rectifier K+ current: a potential mechanism of the proarrhythmic effects of methanesulfonanilideclass III agents.

OBJECTIVE: To elucidate the regional difference of the K+ current blocking effects of methanesulfonanilide class III agents. METHODS: Regional differences in action potential duration (APD) and E-4031-sensitive component (IKr) as well as -insensitive component (IKs) of the delayed rectifier K+ current (IK) were investigated in enzymatically isolated myocytes from apical and basal regions of the rabbit left ventricle using the whole-cell clamp technique. RESULTS: At 1 Hz stimulation, APD was significantly longer in the apex than in the base (223.1 +/- 10.6 vs. 182.7 +/- 14.5 ms, p < 0.05); application of 1 microM E-4031 caused more significant APD prolongation in the apex than in the base (32.5 +/- 6.4% vs. 21.0 +/- 8.8%, p < 0.05), resulting in an augmentation of regional dispersion of APD. In response to a 3-s depolarization pulse to +40 mV from a holding potential of -50 mV, both IK tail and IKs tail densities were significantly smaller in apical than in basal myocytes (IK: 1.56 +/- 0.13 vs. 2.09 +/- 0.21 pA/pF, p < 0.05; IKs: 0.40 +/- 0.15 vs. 1.43 +/- 0.23, p < 0.01), whereas IKr tail density was significantly greater in the apex than in the base (1.15 +/- 0.13 vs. 0.66 +/- 0.11 pA/pF, p < 0.01). The ratio of IKs/IKr for the tail current in the apex was significantly smaller than that in the base (0.51 +/- 0.21 vs. 3.09 +/- 0.89; p < 0.05). No statistical difference was observed in the voltage dependence as well as activation and deactivation kinetics of IKr and IKs between the apex and base. Isoproterenol (1 microM) increased the time-dependent outward current of IKs by 111 +/- 8% during the 3-s depolarizing step at +40 mV and its tail current by 120 +/- 9% on repolarization to the holding potential of -50 mV, whereas it did not affect IKr. CONCLUSIONS: The regional differences in IK, in particular differences in its two components may underlie the regional disparity in APD, and that methanesulfonanilide class III antiarrhythmic agents such as E-4031 may cause a greater spatial inhomogeneity of ventricular repolarization, leading to re-entrant arrhythmias.

Hypoxia inhibits the changes in action potentials and ion channels during primary culture of neonatal rat ventricular myocytes.

Action potentials of rat ventricular myocytes are progressively shortened after birth within several weeks mainly due to a progressive increase in transient outward potassium current (I(to)). On the supposition that an elevation in blood oxygen after birth may contribute to such developmental change, we studied effects of long-term exposure to hypoxia on changes in cardiac action potentials and I(to). Single ventricular myocytes isolated from day-old neonatal rat hearts were cultured in normoxic condition (21% O(2)) for 15 days and served as control. To test the influence of long-term exposure to hypoxia, O(2)tension was reduced to 7.5% at day 6 during culture. In 15-day cells cultured in normoxia, action potential duration (APD) was shortened by 44% (n=11) compared with 5-day cells (n=10); cell capacitance was increased to 2.0-fold. I(to)density was increased by 189-265% (n=11) at voltage levels from -20 to 50 mV without any changes in the kinetics of current inactivation. In 15-day cells cultured in hypoxia, APD was shortened only by 16% (n=6) from control; the increment of cell capacitance was 2.1-fold (n=6). The I(to)increment was limited to 53% (n=8); both inactivation and its recovery of the current was apparently slowed due to the amplification of the slower component. These results suggest that the developmental augmentation of I(to)expression during culture requires oxygen and the increase in I(to)and cell hypertrophy are likely regulated independently.