Minimum Information about a Cardiac Electrophysiology Experiment (MICEE): standardised reporting for model reproducibility, interoperability, and data sharing.

Cardiac experimental electrophysiology is in need of a well-defined Minimum Information Standard for recording, annotating, and reporting experimental data. As a step towards establishing this, we present a draft standard, called Minimum Information about a Cardiac Electrophysiology Experiment (MICEE). The ultimate goal is to develop a useful tool for cardiac electrophysiologists which facilitates and improves dissemination of the minimum information necessary for reproduction of cardiac electrophysiology research, allowing for easier comparison and utilisation of findings by others. It is hoped that this will enhance the integration of individual results into experimental, computational, and conceptual models. In its present form, this draft is intended for assessment and development by the research community. We invite the reader to join this effort, and, if deemed productive, implement the Minimum Information about a Cardiac Electrophysiology Experiment standard in their own work.

Association of aortic valve sclerosis with thrombin generation in hypertensive patients.

Aortic valve sclerosis (AVS) may predispose to a prothrombotic state, as AVS is predictor of cardiovascular events in hypertensive populations. Thrombin exerts non-thrombotic effects such as vessel tone regulation, progression of atherosclerosis and stimulation of atrial natriuretic peptide (ANP) secretion. We hypothesized that hypertensive patients with AVS may have a persistently activated thrombin generation. We studied 234 asymptomatic never-treated hypertensive patients (73 of them with AVS). Prothrombin F1+2 (F1+2), as a marker of thrombin generation and fibrin D-dimer, as a marker of thrombus formation, ANP and brain natriuretic peptide (BNP) were measured. Presence of AVS, aortic jet velocity and left ventricular diameter at diastole were determined by echocardiography. Glomerular filtration rate was estimated using the Modification of Diet in Renal Disease formula. F1+2 (median and interquartile range (IQR) = 1.05, 0.87-1.38 nM vs. 0.93, 0.72-1.16) and ANP (22, 14-37 pg ml(-1) vs. 17, 11-25) levels were greater, and glomerular filtration rate values (65+/-9 ml min(-1)/1.73 m2 vs. 68+/-11) were lower in hypertensive patients with AVS than in those without AVS. F1+2 (odds ratio, 95% CI = 2.94, 1.07-8.6) was independently associated with AVS after being adjusted for age, gender and the variables of cardiorenal functions measured. After 6 months of treatment using valsartan, F1+2 levels remained elevated in hypertensive patients with AVS (1.14, 0.83-1.42 nM vs. 1.07, 0.84-1.5, n=19), but decreased in those without AVS (1.01, 0.85-1.31 vs. 0.8, 0.84-1.78, n=27). Thrombin generation was associated with AVS in untreated hypertensive patients, and this association was persistent after blood-pressure-lowering treatment using valsartan.

Predictive value of von Willebrand factor for adverse clinical outcome in hypertensive patients with mild-to-moderate aortic regurgitation.

Plasma levels of von Willebrand factor (vWF), a marker of endothelial dysfunction/damage, are elevated in high-risk hypertensive patients and in patients with severe aortic regurgitation (AR). Patients with mild-to-moderate AR, frequently detected in hypertensive elderly, have additional left ventricular morphological and functional dysfunctions. We hypothesized that hypertensive patients with mild-to-moderate AR may have enhanced endothelial and/or left ventricular dysfunctions that may lead to a deteriorated prognosis. We measured vWF, prothrombin F1+2 (F 1+2) as a marker of thrombin generation, brain natriuretic peptide (BNP) in 104 hypertensive patients with mild-to-moderate AR and 66 hypertensive patients without AR. The left ventricular diameter at systole (LVDs) and left ventricular posterior wall thickness (LVWT) were determined by echocardiography and indexed by body surface area (LVDs/BSA and LVWT/BSA). VWF (median, interquartile range (IQR) 154, 120-196%) and BNP (34.7 pg ml(-1), 15-65%) levels were greater in patients with AR than in those without AR (135, 98-175% and 20, 10.3-49 pg ml(-1)). All patients were prospectively followed up for cardiac events during the period of median 43 months (IQR 31-81). Patients with AR had an increased risk of cardiac events (regression ratio (RR) 1.87, 95% confidence interval 1.28-2.87) when compared to those without AR. A multivariate Cox hazard analysis indicated that log vWF (RR 4.93) and log BNP (RR 1.9) were independent predictors in patients with AR. VWF was an independent predictor of clinical outcome in hypertensive patients with mild-to-moderate AR.

Risk of vertebral osteoporosis in post-menopausal women with alterations of the mandible.

BACKGROUND: Previous studies have suggested that a thin or eroded cortex of the mandible detected on dental panoramic radiographs is associated with low vertebral bone mineral density (BMD) or osteoporosis. However, those studies did not estimate the multivariate-adjusted risk for low vertebral BMD or osteoporosis associated with alterations of the mandible. METHODS: BMD of the lumbar vertebrae (L2-L4) was compared among quartiles of cortical width and among three cortical shape categories in 450 post-menopausal women (mean age, 57.2 years), adjusted for potential confounders. The odds ratios for low BMD or osteoporosis according to cortical width and shape were also calculated. RESULTS: Significant associations were found between cortical width and shape, and vertebral BMD. The odds ratios for low vertebral BMD associated with the second, third and lowermost quartiles of cortical width were 1.71 (95% confidence interval (CI), 0.96-3.05), 2.30 (95% CI, 1.29-4.11) and 5.43 (95% CI, 2.16-10.71), respectively, compared with the uppermost quartile. The odds ratios for osteoporosis according to cortical width category were similar to those for low BMD. The odds ratios for low BMD associated with mildly to moderately and severely eroded cortices were 3.85 (95% CI, 2.37-6.25) and 7.84 (95% CI, 2.57-23.90), respectively, compared with normal cortex. The odds ratios for osteoporosis associated with mildly to moderately and severely eroded cortices were 4.73 (95% CI, 2.54-8.80) and 14.73 (95% CI, 6.14-35.47), respectively. CONCLUSIONS: Post-menopausal women with alterations of the mandible may have an increased risk for low vertebral BMD or osteoporosis.

Diagnostic efficacy of alveolar bone loss of the mandible for identifying postmenopausal women with femoral osteoporosis.

OBJECTIVES: Mandibular cortical width (MCW) detected on panoramic radiographs may be useful for identifying postmenopausal women with osteoporosis. There is little known regarding whether alveolar bone loss (ABL) of the mandible detected on panoramic radiographs is a potentially accurate screening tool for osteoporosis in comparison with MCW. The purpose of this study was to evaluate whether ABL of the mandible on panoramic radiographs is useful for identifying femoral osteoporosis in postmenopausal women in comparison with MCW. METHODS: Three hundred and fifty-four Japanese postmenopausal women (mean age+/-SD, 56.8+/-7.7 years) were recruited for this study. Femoral BMD was measured by dual energy X-ray absorptiometry. Panoramic radiographs were obtained to estimate ABL of the mandible and MCW. RESULTS: A multiple regression analysis revealed that femoral BMD was significantly associated with MCW (P<0.001), weight (P<0.001), age (P<0.001) and ABL of the mandible (P=0.029; adjusted r(2)=0.380). The area under the ROC curve (AUC) for identifying femoral osteoporosis was 0.609 [95% confidence interval (CI), 0.523-0.696] for ABL of the mandible and 0.779 (95% CI, 0.713-0.844) for MCW, respectively. AUC for ABL of the mandible indicated less accuracy. CONCLUSIONS: Our results suggest that ABL of the mandible on panoramic radiographs may not be useful for identifying postmenopausal women with femoral osteoporosis in comparison with MCW.

Predictive value of heart-type fatty acid-binding protein for left ventricular remodelling and clinical outcome of hypertensive patients with mild-to-moderate aortic valve diseases.

Heart-type fatty acid-binding protein (H-FABP), a marker of acute myocardial infarction and a soluble cytosolic protein, may be released following left ventricular remodelling in cardiac overloaded hearts caused by hypertension, aortic regurgitation (AR) or aortic stenosis (AS). Our aim was to investigate if H-FABP levels are associated with left ventricular remodelling and clinical outcome in hypertensive patients with AR or AS. H-FABP and brain natriuretic peptide (BNP) were measured, glomerular filtration rate (GFR) was estimated using the modification of diet in renal disease (MDRD) equation, and left ventricular dimension at systole corrected for body surface area (LVDs/BSA) and relative wall thickness (RWT) were determined by echocardiography in hypertensive patients with mild-to-moderate AR (n=78), those with mild-to-moderate AS (n=73) and those without valvular heart diseases (HT) (n=50). H-FABP levels were significantly higher in AR (4.9+/-3 ng/ml) and in AS (4.5+/-3) than in HT (3.4+/-1) and BNP (65+/-73 pg/ml, 76+/-75, 35+/-22). H-FABP correlated with LVDs/BSA in AR (beta=0.23, P<0.05), and RWT in AS (beta=0.18, P<0.05) after adjustment for age, gender and all the other variables. AS and AR patients were prospectively followed up for cardiac events during 34+/-19 months. A multivariate Cox hazard analysis indicated H-FABP was an independent predictor of outcome both in AR (relative risk (RR)=7.61, 95% CI=2.39-25.3) and AS (RR=13.6, 95% CI=3.27-66.9). H-FABP, associated with left ventricular remodelling, is useful in predicting clinical outcome in hypertensive patients with mild-to-moderate aortic valve diseases.

Diagnostic performance of general dental practitioners after lecture in identifying post-menopausal women with low bone mineral density by panoramic radiographs.

OBJECTIVES: Mandibular cortical erosion detected on panoramic radiographs may be useful for identifying post-menopausal women with low skeletal bone mineral density (BMD). The purposes of this study were to calculate the diagnostic performance of general dental practitioners (GDPs) who attended a lecture on identifying post-menopausal women with low BMD from findings on panoramic radiographs and to evaluate the influence of GDPs' age on diagnostic performance. METHODS: After a 1 h lecture, 111 GDPs were asked to classify the mandibular cortex (normal or eroded) on panoramic radiographs obtained from 100 post-menopausal women who have had skeletal BMD assessment. Low BMD was defined as a BMD T score of -1.0 or less. Diagnostic performance was analysed by comparing two groups classified by mandibular cortex (women with normal cortex and women with any eroded cortex) with those classified by BMD (women with normal BMD and women with low BMD). RESULTS: The mean sensitivity, specificity, positive predictive value, negative predictive value, accuracy and likelihood ratio for a positive risk result were 73.0% (95% confidence interval [CI]; 71.3 to 74.7%), 49.0% (95% CI; 46.4 to 51.5%), 66.9% (95% CI; 66.0 to 67.8%), 57.0% (95% CI; 55.8 to 58.2%), 62.9% (95% CI; 62.1 to 63.7%) and 1.51 (95% CI; 1.44 to 1.58), respectively. GDPs' age did not influence diagnostic performance. CONCLUSIONS: Our results suggest that 73.0% of women who had low skeletal BMD can be identified by GDPs after a lecture on the use of panoramic radiographs as an aid in diagnosing low BMD; however, the diagnostic performance may not be influenced by GDPs' age.

Involvement of reduced sensitivity to Ca in beta-adrenergic action on airway smooth muscle.

BACKGROUND: It is well known that beta-adrenoceptor agonists (beta-agonists) cause relaxation in airway smooth muscle mediated by a reduction in the concentration of intracellular Ca2+ ([Ca2+](i)). However, little is currently known regarding whether reduced sensitization to Ca2+ is involved in the beta-adrenergic relaxation. OBJECTIVE: This study was designed to determine the intracellular mechanisms underlying suppression of Ca2+ sensitization in beta-adrenergic relaxation (Ca(2+)-independent relaxation by beta-agonists). Methods Isometric tension and [Ca2+](i) were simultaneously measured in fura-2-loaded strips isolated from guinea-pig tracheal smooth muscles. The relationships between tension and [Ca2+](i) were examined in the inhibitory action of isoprenaline (ISO) and other cAMP-related agents against methacholine-induced contraction. RESULTS: The concentration-inhibition curve for ISO against methacholine in tension was significantly dissociated from the curve for ISO in [Ca2+](i). In ISO-induced relaxation, a reduction in tension was significantly greater than that in [Ca2+](i.) This phenomenon was mimicked by other cAMP-related agents: forskolin and dibutyryl-cAMP. In contrast, the inhibitory action of SKF-96365, a non-selective inhibitor of Ca(2+) channels, was associated with that in [Ca2+](i). In the presence of Rp-cAMPS, an inhibitor of protein kinase A (PKA), ISO caused an equivalent relaxation with less reduction in [Ca2+](i). The effects of ISO were not affected by Y-27632, an inhibitor of Rho-kinase, or by bisindolylmaleimide, an inhibitor of protein kinase C. ISO failed to inhibit contraction elicited by calyculin A, an inhibitor of myosin phosphatase. Conclusion beta-Adrenergic action antagonizes not only Ca2+ mobilization but also Ca2+ sensitization in methacholine-induced contraction. The cAMP/PKA-independent, G(s)-direct action is more potent in Ca(2+)-independent relaxation by beta-agonists than the cAMP/PKA-dependent pathway. Moreover, myosin phosphatase is a fundamentally affected protein in the reduced response to Ca2+ mediated by beta-agonist. Our results may provide evidence that this Ca2+ desensitization is a novel target for a reliever medication using rapid-acting beta-agonists in acute asthma management.

Computer three-dimensional reconstruction of the sinoatrial node.

BACKGROUND: There is an effort to build an anatomically and biophysically detailed virtual heart, and, although there are models for the atria and ventricles, there is no model for the sinoatrial node (SAN). For the SAN to show pacemaking and drive atrial muscle, theoretically, there should be a gradient in electrical coupling from the center to the periphery of the SAN and an interdigitation of SAN and atrial cells at the periphery. Any model should include such features. METHODS AND RESULTS: Staining of rabbit SAN preparations for histology, middle neurofilament, atrial natriuretic peptide, and connexin (Cx) 43 revealed multiple cell types within and around the SAN (SAN and atrial cells, fibroblasts, and adipocytes). In contrast to atrial cells, all SAN cells expressed middle neurofilament (but not atrial natriuretic peptide) mRNA and protein. However, 2 distinct SAN cell types were observed: cells in the center (leading pacemaker site) were small, were organized in a mesh, and did not express Cx43. In contrast, cells in the periphery (exit pathway from the SAN) were large, were arranged predominantly in parallel, often expressed Cx43, and were mixed with atrial cells. An approximately 2.5-million-element array model of the SAN and surrounding atrium, incorporating all cell types, was constructed. CONCLUSIONS: For the first time, a 3D anatomically detailed mathematical model of the SAN has been constructed, and this shows the presence of a specialized interface between the SAN and atrial muscle.

Analysis of QT Interval Prolongation With Heart Failure by Simulation of Repolarization Process.

It has been postulated that action potential duration (APD) is prolonged and IKs, a slow component of delayed rectifier potassium current, decreases in heart failure. We have reported that QT interval is prolonged and expression weight of KCNE1, coding IKschannel, increases in patients with heart failure. Since it is known that increase in KCNE1 increases the maximum conductance of IKschannel, the mechanism of APD prolongation is not explained by over expression of KCNE1. In this study, we construct a cardiac membrane action potential simulation model based on the experimental data from Xenopus oocytes expressed KCNQ1 and KCNE1 to investigate the relationship between increase in KCNE1 and APD. In addition, we investigated effect of reduction in Ca2+-independent transient outward potassium current (Ito) on APD in heart failure. In simulation, APD at 5ng KCNE1 was 180.96ms, which was 4.63% longer than that at 1ng KCNE1 (APD=172.96ms) and 55.9% longer than that at 0.2ng KCNE1 (APD=110.96ms. In the cases of KCNQ1 alone and 0.2ng KCNE1 coinjected, APD shortened as density of Itodecreased, and APD prolonged as density of Itodecreased in other cases. This study shows that increase in KCNE1 expression level makes maximum conductance of IKschannel increase and IKschannel open slowly and conductance of IKschannel decrease according to the APD time scale. Therefore increasing the KCNE1 expression level may prolong APD with this mechanism. This method of constructing a simulation model based on experiments helps to explain the relationship between potassium currents and QT interval prolongation.

Sarcoplasmic reticulum Ca2+ release is not a dominating factor in sinoatrial node pacemaker activity.

Recent work on isolated sinoatrial node cells from rabbit has suggested that sarcoplasmic reticulum Ca2+ release plays a dominant role in the pacemaker potential, and ryanodine at a high concentration (30 micromol/L blocks sarcoplasmic reticulum Ca2+ release) abolishes pacemaking and at a lower concentration abolishes the chronotropic effect of beta-adrenergic stimulation. The aim of the present study was to test this hypothesis in the intact sinoatrial node of the rabbit. Spontaneous activity and the pattern of activation were recorded using a grid of 120 pairs of extracellular electrodes. Ryanodine 30 micromol/L did not abolish spontaneous activity or shift the position of the leading pacemaker site, although it slowed the spontaneous rate by 18.9+/-2.5% (n=6). After ryanodine treatment, beta-adrenergic stimulation still resulted in a substantial chronotropic effect (0.3 micromol/L isoproterenol increased spontaneous rate by 52.6+/-10.5%, n=5). In isolated sinoatrial node cells from rabbit, 30 micromol/L ryanodine slowed spontaneous rate by 21.5+/-2.6% (n=13). It is concluded that sarcoplasmic reticulum Ca2+ release does not play a dominating role in pacemaking in the sinoatrial node. The full text of this article is available at http://www.circresaha.org.

Carvedilol and vesnarinone: new antiarrhythmic approach in heart failure therapy.

Carvedilol and vesnarinone are drugs attracting recent interest in the treatment of chronic heart failure. Electrophysiologic studies have revealed that these drugs cause a moderate prolongation of action potential duration (APD) of ventricular muscles with minimal "reverse frequency-dependence" through different ionic mechanisms. Carvedilol blocks L-type Ca2+ current (ICa), transient outward K+ current (Ito), and delayed rectifier K+ current (IK) preferentially for the rapidly activating component (IKr). Vesnarinone is a selective blocker of IK with a unique drug-channel interaction. From the voltage- and time-dependence of IK inhibition, vesnarinone is considered to bind the IK (mainly IKr) channel during the activated state and unbind during the closed state. These electropharmacologic profiles provide a new approach for the development of an ideal antiarrhythmic drugs in patients with structural heart diseases.

Estrogen replacement therapy in postmenopausal women augments reactive hyperemia in the forearm by reducing angiotensin converting enzyme activity.

The precise mechanism of the vasoprotective effect of estrogen replacement therapy in postmenopausal women is not fully understood. The present study sought to determine the role of nitric oxide (NO) and angiotensin-converting enzyme (ACE) in the vasodilator response of the forearm vessels induced by estrogen administration to postmenopausal women. Subjects were divided into two groups. One group received conjugated equine estrogen (0.625 mg daily) orally for 3 months (n=26), while the other received no treatment (control group, n=10). Forearm blood flow was measured by strain-gauge plethysmography. The concentrations of nitrite/nitrate (metabolites of NO), ACE activity, and lipid parameters were measured. Basal forearm blood flow, body weight, blood pressure, and heart rate were similar at baseline in both groups. After 3 months of estrogen administration, the maximal forearm blood flow response during reactive hyperemia and the serum level of nitrite/nitrate each showed a significant increase over baseline values: from 23.6+/-2.0 to 36.5+/-3.1 ml/min per 100 ml tissue (P<0.01), and from 24.8+/-2.3 to 38.6+/-3.6 micromol/l (P<0.01), respectively. Plasma levels of ACE activity were significantly reduced from baseline after 3 months of estrogen treatment (from 12.2+/-0.6 to 10.9+/-0.6 IU/l, P<0.01). No changes were seen in controls. The change in forearm blood flow after sublingual nitroglycerin was similar at baseline versus after 3 months of estrogen administration. The increase in the serum level of nitrite/nitrate after 3 months of estrogen therapy showed a significant inverse correlation (r=0.52, P<0.01) with the reduction in the plasma level of ACE activity. There was no significant correlation between the increase in serum nitrite/nitrate and any change in serum lipids, blood pressure, or other parameters. The administration of oral estrogen to postmenopausal women for 3 months increased the NO-mediated forearm endothelium-dependent vasodilatation. This was likely due, at least in part, to ACE inhibition. The latter may be one mechanism by which ERT provides its well-known cardiovascular benefit.

Distribution of the muscarinic K+ channel proteins Kir3.1 and Kir3.4 in the ventricle, atrium, and sinoatrial node of heart.

The functionally important effects on the heart of ACh released from vagal nerves are principally mediated by the muscarinic K+ channel. The aim of this study was to determine the abundance and cellular location of the muscarinic K+ channel subunits Kir3.1 and Kir3.4 in different regions of heart. Western blotting showed a very low abundance of Kir3.1 in rat ventricle, although Kir3.1 was undetectable in guinea pig and ferret ventricle. Although immunofluorescence on tissue sections showed no labeling of Kir3.1 in rat, guinea pig, and ferret ventricle and Kir3.4 in rat ventricle, immunofluorescence on single ventricular cells from rat showed labeling in t-tubules of both Kir3.1 and Kir3.4. Kir3.1 was abundant in the atrium of the three species, as shown by Western blotting and immunofluorescence, and Kir3.4 was abundant in the atrium of rat, as shown by immunofluorescence. Immunofluorescence showed Kir3.1 expression in SA node from the three species and Kir3.4 expression in the SA node from rat. The muscarinic K+ channel is activated by ACh via the m2 muscarinic receptor and, in atrium and SA node from ferret, Kir3.1 labeling was co-localized with m2 muscarinic receptor labeling throughout the outer cell membrane.

Early and late elevation of plasma atrial and brain natriuretic peptides in patients after bone marrow transplantation.

Clinical usefulness of bone marrow transplantation (BMT) remains limited by myocardial damage during the post-transplantation period. Measurements of plasma atrial and brain natriuretic peptides (ANP, BNP) during the acute post-transplantation period could serve to monitor cardiac complications since these peptides are known to increase in heart failure depending on its severity. We prospectively analyzed ANP and BNP levels from 14 days before to 100 days after BMT in 46 consecutive patients undergoing allogeneic (n=42) and autologous (n=4) transplantation. Cardiac performance was assessed by echocardiography and radionuclide ventriculography. BNP and ANP levels of the patients on admission (baseline: day-14) were 16.3+/-13.3 pg/ml and 14.4+/-8.8 pg/ml, respectively. There were two different types of changes in the BNP and ANP levels. The 21 patients in group I showed dual peaks of elevation on day 1 (BNP=164.4+/-136.0 pg/ml, P<0.01; ANP=44.5+/-35.4 pg/ml, NS) and day 14 (BNP=233.9+/-106.2 pg/ml, P<0.01; ANP=142.7+/-154.6 pg/ml, P<0.05), whereas the remaining 25 patients in group II had a single peak on day 1 (BNP=124.5+/-124.9 pg/ml, P<0.05; ANP=45.2+/-42.4 pg/ml, NS). The left ventricular ejection fraction on day 63 was unchanged in both groups of patients from the baselines. The time to peak filling rate, a parameter of diastolic function in the radionuclide ventriculography, was significantly prolonged in group I patients (by 30+/-53%), whereas unaffected in group II patients. These results suggest that plasma BNP monitoring for 2 weeks after BMT may be useful for early detection of patients at high risk for cardiac dysfunction in the post-transplantation period.

Heterogeneous expression of the delayed-rectifier K+ currents i(K,r) and i(K,s) in rabbit sinoatrial node cells.

1. The electrical activity of sinoatrial node cells is heterogeneous. To understand the reasons for this, the density of the delayed-rectifier K+ current and its two components, i(K,r) and i(K,s), as a function of the size (as measured by cell capacitance) of rabbit sinoatrial node cells was investigated using the whole-cell voltage-clamp technique at 35 degrees C. 2. i(K,r) and i(K,s) were isolated using E-4031 and 293B. Features of the E-4031-sensitive and 293B-insensitive currents corresponded well to those of i(K,r), while features of the E-4031-insensitive and 293B-sensitive currents corresponded well to those of i(K,s). 3. The densities of the outward current under control conditions and the drug-sensitive and -insensitive currents were significantly (P < 0.01) correlated with cell capacitance, with current densities being greater in larger cells. 4. The effects of partial blockade of i(K,r) by 0.1 microM E-4031 on spontaneous action potentials were greater in smaller cells. 5. It is concluded that there are cell size-dependent differences in the density of the i(K,r) and i(K,s) components, and these may be involved in the heterogeneity of the electrical activity of single sinoatrial node cells as well as that of the intact sinoatrial node.

Density and kinetics of I(Kr) and I(Ks) in guinea pig and rabbit ventricular myocytes explain different efficacy of I(Ks) blockade at high heart rate in guinea pig and rabbit: implications for arrhythmogenesis in humans.

BACKGROUND: Class III antiarrhythmic agents commonly exhibit reverse frequency-dependent prolongation of the action potential duration (APD). This is undesirable because of the danger of bradycardia-related arrhythmias and the limited protection against ventricular tachyarrhythmias. The effects of blockade of separate components of delayed rectifier K(+) current (I(K)) may help to develop agents effective at high heart rate. METHODS AND RESULTS: We assessed the density and kinetics of the 2 components of the delayed rectifier K(+) current, I(Kr) and I(Ks), in rabbit and guinea pig ventricular myocytes. The effects of their specific blockers (chromanol 293B for I(Ks) and E-4031 for I(Kr)) on the action potential was studied at different heart rates by use of whole-cell patch-clamp techniques. In guinea pig ventricular myocytes only, blockade of I(Ks) causes APD prolongation in a frequency-independent manner, whereas blockade of I(Ks) in rabbit ventricular myocytes shows reverse frequency dependence, as does blockade of I(Kr) in both species. This result can be explained primarily by the higher density of I(Ks) in guinea pig ventricle and by its slow deactivation kinetics, which allows I(Ks) to accumulate at high heart rate because little time is available for complete deactivation of it during diastole. CONCLUSIONS: Density and kinetics of components of I(K) explain why blockade of I(Ks) is more effective at high heart rate in the guinea pig ventricle than in the rabbit ventricle, without adverse effects at low heart rate.

Carvedilol: molecular and cellular basis for its multifaceted therapeutic potential.

Carvedilol is a unique cardiovascular drug of multifaceted therapeutic potential. Its major molecular targets recognized to date are membrane adrenoceptors (beta 1, beta 2, and alpha 1), reactive oxygen species, and ion channels (K+ and Ca2+). Carvedilol provides prominent hemodynamic benefits mainly through a balanced adrenoceptor blockade, which causes a reduction in cardiac work in association with peripheral vasodilation. This drug assures remarkable cardiovascular protection through its antiproliferative/atherogenic, antiischemic, antihypertrophic, and antiarrhythmic actions. These actions are a consequence of its potent antioxidant effects, amelioration of glucose/lipid metabolism, modulation of neurohumoral factors, and modulation of cardiac electrophysiologic properties. The usefulness of carvedilol in the treatment of hypertension, ischemic heart disease, and congestive heart failure is based on a combination of hemodynamic benefits and cardiovascular protection.

Open channel block of HERG K(+) channels by vesnarinone.

Vesnarinone, a cardiotonic agent, blocks I(Kr) and, unlike other I(Kr) blockers, produces a frequency-dependent prolongation of action potential duration (APD). To elucidate the mechanisms, we studied the effects of vesnarinone on HERG, the cloned human I(Kr) channel, heterologously expressed in Xenopus laevis oocytes. Vesnarinone caused a concentration-dependent inhibition of HERG currents with an IC(50) value of 17.7 +/- 2.5 microM at 0 mV (n = 6). When HERG was coexpressed with the beta-subunit MiRP1, a similar potency for block was measured (IC(50): 15.0 +/- 3.0 microM at 0 mV, n = 5). Tonic block of the HERG channel current was minimal (<5% at 30 microM, n = 5). The rate of onset of block and the steady-state value for block of current were not significantly different for test potentials ranging from -40 to +40 mV [time constant (tau) = 372 +/- 76 ms at +40 mV, n = 4]. Recovery from block at -60, -90, and -120 mV was not significantly different (tau = 8.5 +/- 1.5 s at -90 mV, n = 4). Vesnarinone produced similar effects on inactivation-removed mutant (G628C/S631C) HERG channels. The IC(50) value was 10.7 +/- 3.7 microM at 0 mV (n = 5), and the onset and recovery from block of current findings were similar to those of wild-type HERG. Amino acids important for the binding of vesnarinone were identified using alanine-scanning mutagenesis of residues believed to line the inner cavity of the HERG channel. Six important residues were identified, including G648, F656, and V659 located in the S6 domain and T623, S624, and V625 located at the base of the pore helix. These residues are similar but not identical to those determined previously for MK-499, an antiarrhythmic drug. In conclusion, vesnarinone preferentially blocks open HERG channels, with little effect on channels in the rested or inactivated state. These actions may contribute to the favorable frequency-dependent prolongation in APD.