Association between 10-Year Atherosclerotic Cardiovascular Disease Risk and Vascular Endothelial Function in Patients with Vasospastic Angina

BACKGROUND

Endothelial dysfunction is a predictor of atherosclerotic cardiovascular disease (ASCVD) and plays an important role in vasospastic angina (VA).

OBJECTIVES

This study evaluated whether flow-mediated dilation (FMD) is also a good marker of 10-year ASCVD risk (10Y-ASCVDR) in patients with VA.

METHODS

Based on their clinical history and coronary artery diameter stenosis (DS), patients were retrospectively enrolled into VA (DS <50% and positive ergonovine provocation), minor coronary artery disease (mCAD, DS <30%), and significant coronary artery disease (sCAD, DS ≥50%) groups. Endothelial function was evaluated by FMD.

RESULTS

Each group contained 50 patients. The 10Y-ASCVDR was significantly higher in the sCAD group than in the VA and mCAD groups (10.86 ± 7.30, 4.71 ± 4.04, and 4.77 ± 4.30, respectively, p < 0.001). The FMD was significantly higher in the mCAD group than in the VA and sCAD groups (6.37 ± 4.25, 3.10 ± 2.23, and 3.07 ± 1.89, respectively, p < 0.001). A significant correlation was found between the FMD and 10Y-ASCVD in the mCAD group (r = -0.622, p < 0.001) and the sCAD group (r = -0.557, p < 0.001) but not in the VA group (r = -0.193, p = 0.179). After adjusting for potential confounders such as BMI, C-reactive protein, maximal coronary stenosis, and brachial-ankle pulse wave velocity, multivariate analysis showed that FMD was independently associated with 10Y-ASCVDR in all patients. However, when looking only at the VA group, FMD did not correlate independently with 10Y-ASCVDR.

CONCLUSIONS

Unlike mCAD and sCAD, we found no correlation between 10Y-ASCVDR and endothelial function in VA. Thus, our results support that FMD is not a good marker of atherosclerotic cardiovascular risk in VA.

Preoperative Cessation of Both Dual Anti-Platelet Agents Is Safe after 1 Year in Patients Receiving Percutaneous Coronary Intervention

Objective

The aim of this study was to investigate the atherothrombotic and bleeding risk of discontinuing both components of dual antiplatelet therapy (DAPT) before surgery in patients with an intracoronary stent after 1 year.

Methods

We retrospectively enrolled 212 patients who received an evaluation of perioperative cardiac risk and underwent surgery from March 2017 to March 2019. We divided them into 2 groups: the discontinuation of both antiplatelet agents group (DCAP, no use of any antiplatelet agent) and the continuation of at least 1 antiplatelet agent group (CAP). The primary composite endpoint was the occurrence of major adverse cardiovascular events (MACE), including death, angina, postoperative coronary angiography, stroke, and readmission within 30 days postoperatively. The second endpoint was bleeding requiring the transfusion of ≥2 packs of red blood cells (RBCs).

Result

A total of 136 patients were enrolled in the study, with 68 in the DCAP group and 68 in the CAP group. The occurrence of MACE did not significantly differ between the groups (25% vs. 17.6%, p=0.295). The incidence of bleeding that required a transfusion was higher in the CAP group (16.2% vs. 30.9%, p=0.044). The postoperative change in hemoglobin levels (-1.9 g/dL vs. -1.8 g/dL, p=0.742), and the number of transfused packs of RBCs (3.5 vs. 5.3, p=0.347) were not significantly different between the groups.

Conclusion

Preoperative discontinuation of DAPT did not increase the risk of MACE. However, continuation of at least 1 antiplatelet agent increased the incidence of bleeding requiring RBC transfusion. Further research with a large cohort is warranted.

Mental health states and influencing factors of risky and problem drinking in South Korean female adolescents

OBJECTIVES

Alcohol is one of the most used and abused psychoactive substances by adolescents. We investigated influencing factors of risky and problem drinking in Korean female adolescents.

STUDY DESIGN

The study design used is a cross-sectional modeling.

METHODS

We used data from the 13th Korean Youth Risk Behavior Web-based Survey (KYRBS) conducted in 2017. KYRBS data were obtained from a stratified, multistage, clustered sample. Risky drinking was binge drinking and problem drinking was drinking with several conflicts association with alcohol consumption.

RESULTS

Among 62,276 participants, the rates of current, risky, and problem drinking among all participants were 16.1%, 8.3%, and 6.1%, respectively. Although all of these rates were higher in males, risky and problem drinking rates among current female drinkers were higher than those of males (55.4 vs 48.5%, 38.9 vs 37.2%, respectively). Problem drinking was most strongly associated with risky drinking (adjusted odds ratio: 17.53 [95% confidence interval: 14.63-21.00]), similarly, risky drinking was most strongly associated with problem drinking in female current drinkers (17.76 [14.84-21.27]). Current smoking was the second strongest risk factor for risky and problem drinking in females (5.22 [3.92-6.95] and 2.93 [2.21-3.89], respectively).

CONCLUSION

Many female adolescents in Korea drink alcohol in an unhealthy manner. The female risky and problem drinking rates among current drinkers were higher than those of males. Risky drinking and problem drinking was most significant influencing factor among females, reciprocally. Public education on abstinence in female adolescents is warranted.

Predictors of survival following veno-arterial extracorporeal membrane oxygenation in patients with acute myocardial infarction-related refractory cardiogenic shock: clinical and coronary angiographic factors

Background

This study aimed to identify the determinant factors of survival in patients with acute myocardial infarction (AMI) and refractory cardiogenic shock (RCS) who underwent veno-arterial extracorporeal membrane oxygenation (ECMO).

Methods

Sixty-nine consecutive patients with AMI-related RCS were enrolled in the study. They were treated with ECMO and primary percutaneous coronary intervention (PCI). The clinical scores and coronary angiography (CAG) factors related to 100-day survival were evaluated.

Results

Thirty patients (43.5%) survived for more than 100 days. The CAG showed that 19 (27.5%) patients had left main disease (LMD). There were 17 (24.6%), 27 (39.1%), and 25 (36.3%) patients with one-vessel, two-vessel, and three-vessel disease, respectively. There were significant differences between the survivors and non-survivors in the simplified acute physiology score II (SAPSII) (65.4±17.2 vs. 83.1±13.0, P<0.001), sepsis-related organ failure assessment score (SOFA) (10.4±2.7 vs. 12.3±2.5, P=0.004), survival after veno-arterial extracorporeal membrane oxygenation score (SAVE) (-4.4±4.3 vs. -8.4±3.1, P<0.001), CPR time (15.8±16.6 vs. 30.0±29.5, P=0.048), LMD [4 (13.3%) vs. 15 (38.5%), P=0.029], and number of coronary artery disease (NCAD) (P<0.001). Multivariate logistic regression analysis showed that NCAD (OR 3.788, P=0.008) was one of the independent predictors of mortality. The ROC analysis showed that SAPSII (AUC 0.786, P<0.001), SOFA (AUC 0.715, P=0.002), and SAVE (AUC 0.766, P<0.001) equally predict mortality. The combined NCAD parameters more accurately predicted mortality and differences in the AUC values (d-AUC) between SAPSII plus NCAD vs. SAPSII (d-AUC 0.073, z=2.256, P=0.024), SOFA plus NCAD vs. SOFA (d-AUC 0.058, z=2.773, P=0.006), and SAVE plus NCAD vs. SAVE (d-AUC 0.036, z=2.332, P=0.020).

Conclusions

The SAPSII, SOFA, and SAVE scores predict the prognosis of ECMO-treated AMI patients with RCS. The CAG findings reinforce the predictive power of each score.

Efficacy and Safety of Omega-3 Fatty Acids in Patients Treated with Statins for Residual Hypertriglyceridemia: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

BACKGROUND

Cardiovascular risk remains increased despite optimal low density lipoprotein cholesterol (LDL-C) level induced by intensive statin therapy. Therefore, recent guidelines recommend non-high density lipoprotein cholesterol (non-HDL-C) as a secondary target for preventing cardiovascular events. The aim of this study was to assess the efficacy and tolerability of omega-3 fatty acids (OM3-FAs) in combination with atorvastatin compared to atorvastatin alone in patients with mixed dyslipidemia.

METHODS

This randomized, double-blind, placebo-controlled, parallel-group, and phase III multicenter study included adults with fasting triglyceride (TG) levels ≥200 and <500 mg/dL and LDL-C levels <110 mg/dL. Eligible subjects were randomized to ATOMEGA (OM3-FAs 4,000 mg plus atorvastatin calcium 20 mg) or atorvastatin 20 mg plus placebo groups. The primary efficacy endpoints were the percent changes in TG and non-HDL-C levels from baseline at the end of treatment.

RESULTS

After 8 weeks of treatment, the percent changes from baseline in TG (-29.8% vs. 3.6%, P<0.001) and non-HDL-C (-10.1% vs. 4.9%, P<0.001) levels were significantly greater in the ATOMEGA group (n=97) than in the atorvastatin group (n=103). Moreover, the proportion of total subjects reaching TG target of <200 mg/dL in the ATOMEGA group was significantly higher than that in the atorvastatin group (62.9% vs. 22.3%, P<0.001). The incidence of adverse events did not differ between the two groups.

CONCLUSION

The addition of OM3-FAs to atorvastatin improved TG and non-HDL-C levels to a significant extent compared to atorvastatin alone in subjects with residual hypertriglyceridemia.

Association Between Intra-arterial Invasive Central and Peripheral Blood Pressure and Endothelial Function (Assessed by Flow-Mediated Dilatation) in Stable Coronary Artery Disease

BACKGROUND

Endothelial function is an independent predictor of coronary artery disease (CAD) and is regulated by a number of factors, including blood pressure.

OBJECTIVES

The current study was designed to test the hypothesis that intra-arterial invasive central blood pressure is strongly associated with endothelial function in patients with CAD.

METHODS

In patient with CAD (diameter stenosis ≥30%), invasive central (aortic) and left peripheral (brachial) blood pressures were determined during transradial coronary angiography. The endothelial function was evaluated by way of flow-mediated dilatation (FMD) of the brachial artery.

RESULTS

We enrolled 413 consecutive patients. There were 260 patients with significant CAD (sCAD, diameter stenosis ≥50%) and 153 patients with nonsignificant CAD (nsCAD, diameter stenosis <50% and ≤30%). FMD was significantly and inversely correlated with central and peripheral parameters in terms of systolic blood pressure, mean arterial pressure, and pulse pressure (PP) (r = -0.332, r = -0.184, and r = -0.407, respectively, all P < 0.001) and (r = -0.303, r = -0.190, and r = -0.319, respectively, all P < 0.001). Compared with sCAD, there was closer correlation between central PP with FMD in nsCAD (r = -0.548 vs. r = -0.345, both P < 0.001). After adjusting potential confounders such as age, body mass index and high-sensitivity C-reactive protein, multivariate analysis showed that FMD remained independently associated with central PP, degree of coronary artery stenosis, and brachial-ankle pulse wave velocity in all patients. In patients with nsCAD, the multivariate analysis showed that only central PP was independently correlated with FMD.

CONCLUSIONS

In patients with stable CAD, a decline in endothelial function is most closely associated with invasive central pulse pressure.

Clinical Meaning of the Ratio of Brachial Pre-Ejection Period to Brachial Ejection Time in Patients with Left Ventricular Systolic Dysfunction

An increase in the ratio of the brachial pre-ejection period to brachial ejection time [pre-ejection period (PEP)/ET] is correlated with a decrease of left ventricular ejection fraction (LVEF). The current study was designed to test the hypothesis that the change value (Δ) of PEP/ET is a useful indicator of Δ LVEF in patients with left ventricular systolic dysfunction.We consecutively enrolled 104 patients with left ventricular systolic dysfunction (LVEF < 45%). PEP/ET, B-type natriuretic peptide (BNP), and LVEF were evaluated at baseline and at 6-month follow-up. Compared with the baseline measurements, the 6-month values of ΔLVEF, ΔBNP, and ΔPEP/ET were 9.8% ± 9.0% (from 36.3% ± 9.2% to 46.3% ± 12.5%, P < 0.001), -168.5 ± 255.4 (from 271.4 ± 282.5 to 104.1 ± 129.6, P < 0.001), and -0.060 ± 0.069 (from 0.413 ± 0.097 to 0.358 ± 0.079, P < 0.001), respectively. There were significant correlations between LVEF and PEP/ET and between LVEF and BNP in both the initial (r = -0.316, P = 0.001 and r = -0.598, P < 0.001, respectively) and 6-month follow-up (r = -0.307, P = 0.003 and r = -0.701, P < 0.001, respectively). The Steiger's Z test showed that BNP had a significantly stronger correlation with LVEF compared with the correlations between LVEF and PEP/ET in both the initial and 6-month studies (Z = 2.471, P = 0.013 and Z = 3.575, P < 0.001, respectively). There were also significant correlations between ΔLVEF and ΔPEP/ET (r = -0.515, P < 0.001) and between ΔLVEF and ΔBNP (r = -0.581, P < 0.001); however, there was no difference between the correlations for ΔLVEF and ΔPEP/ET versus ΔLVEF and ΔBNP (Steiger's Z = 0.600, P = 0.545).In patients with left ventricular systolic dysfunction not only ΔBNP but also ΔPEP/ET could be a simple indicator of predicting change of LVEF.

Endothelial Function and Cardiovascular Autonomic Activity in Neurally Mediated Syncope

OBJECTIVES

The aim of this study was to investigate endothelial function and cardiovascular autonomic activity in patients with neurally mediated syncope (NMS).

METHODS

Patients with a typical history of NMS were divided according to the result of a head-up tilt (HUT) test. There were 25 patients each in the HUT-positive (HUT+), HUT-negative (HUT-) and control groups. Flow-mediated dilation (FMD) and 24-hour ambulatory electrocardiography (AECG) were performed before the HUT tests.

RESULTS

The HUT+ group had a significantly higher FMD than that of the HUT- group and the control group (8.8 ± 3.3 vs. 6.4 ± 2.9%, p = 0.006, and 8.8 ± 3.3 vs. 5.7 ± 2.2%, p = 0.001, respectively). On a 24-hour AECG, the parasympathetic indexes of time domain, such as rMSSD and the pNN50, were significantly higher in the HUT+ group than in the HUT- group (39.0 ± 9.6 vs. 31.6 ± 9.6 ms, p = 0.016, and 16.5 ± 8.1 vs. 10.2 ± 7.2%, p = 0.002, respectively) and the control group (39.0 ± 9.6 vs. 28.9 ± 9.6%, p = 0.001 and 16.5 ± 8.1 vs. 8.7 ± 6.7%, p = 0.001, respectively). High-frequency spectra (parasympathetic activity) of the frequency domain showed similar results.

CONCLUSIONS

Not only parasympathetic activity, but also endothelial function may affect the results of HUT tests in patients with NMS.

Fluorous-inorganic hybrid dielectric materials for solution-processed electronic devices

Fluorous-inorganic hybrid dielectric (FIHD) materials in fluorous solvents can be deposited on top of organic semiconductor films by solution casting.

Impact of Framingham risk score, flow-mediated dilation, pulse wave velocity, and biomarkers for cardiovascular events in stable angina

Although the age-adjusted Framingham risk score (AFRS), flow-mediated dilation (FMD), brachial-ankle pulse wave velocity (baPWV), high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine, and free fatty acid (FFA) can predict future cardiovascular events (CVEs), a comparison of these risk assessments for patients with stable angina has not been reported. We enrolled 203 patients with stable angina who had been scheduled for coronary angiography (CAG). After CAG, 134 patients showed significant coronary artery disease. During 4.2 yr follow-up, 36 patients (18%) showed CVEs, including myocardial infarction, de-novo coronary artery revascularization, in-stent restenosis, stroke, and cardiovascular death. ROC analysis showed that AFRS, FMD, baPWV, and hsCRP could predict CVEs (with AUC values of 0.752, 0.707, 0.659, and 0.702, respectively, all P<0.001 except baPWV P=0.003). A Cox proportional hazard analysis showed that AFRS and FMD were independent predictors of CVEs (HR, 2.945; 95% CI, 1.572-5.522; P=0.001 and HR, 0.914; 95% CI, 0.826-0.989; P=0.008, respectively). However, there was no difference in predictive power between combining AFRS plus FMD and AFRS alone (AUC 0.752 vs. 0.763; z=1.358, P=0.175). In patients with stable angina, AFRS and FMD are independent predictors of CVEs. However, there is no additive value of FMD on the AFRS in predicting CVEs.

Adenovirus-mediated overexpression of Tcfe3 ameliorates hyperglycaemia in a mouse model of diabetes by upregulating glucokinase in the liver

AIMS/HYPOTHESIS

Transcription factor E3 (TFE3) has been shown to increase insulin sensitivity by activating insulin-signalling pathways. However, the role of TFE3 in glucose homeostasis is not fully understood. Here, we explored the possible therapeutic potential of TFE3 for the control of hyperglycaemia using a streptozotocin-induced mouse model of diabetes.

METHODS

We achieved overabundance of TFE3 in streptozotocin mice by administering an adenovirus (Ad) or adeno-associated virus serotype 2 (AAV2). We also performed an oral glucose tolerance test (OGTT) and insulin tolerance test (ITT). To explore molecular mechanisms of blood glucose control by TFE3, transcriptional studies on the regulation of genes involved in hepatic glucose metabolism were performed using quantitative real-time PCR and chromatin immunoprecipitation assay. The binding site of TFE3 in the liver Gck gene promoter was identified using deletion and site-specific mutation studies.

RESULTS

Overabundance of TFE3 resulted in reduced hyperglycaemia as shown by the OGTT and ITT in streptozotocin-treated mice. We observed that TFE3 can upregulate Gck in a state of insulin deficiency. However, glucose-6-phosphatase and cytosolic phosphoenolpyruvate carboxykinase mRNA levels were decreased by Ad-mediated overexpression of Tcfe3. Biochemical studies revealed that the anti-hyperglycaemic effect of TFE3 is due to the upregulation of Gck. In primary cultured hepatocytes, TFE3 increased expression of Gck mRNA. Conversely, small interfering RNA-mediated knockdown of TFE3 resulted in a decrease in Gck mRNA.

CONCLUSIONS/INTERPRETATION

This study demonstrates that TFE3 counteracts hyperglycaemia in streptozotocin-treated mice. This effect could be due to the upregulation of Gck by binding of TFE3 to its cognitive promoter region.

Superplastic carbon nanotubes

The theoretical maximum tensile strain--that is, elongation--of a single-walled carbon nanotube is almost 20%, but in practice only 6% is achieved. Here we show that, at high temperatures, individual single-walled carbon nanotubes can undergo superplastic deformation, becoming nearly 280% longer and 15 times narrower before breaking. This superplastic deformation is the result of the nucleation and motion of kinks in the structure, and could prove useful in helping to strengthen and toughen ceramics and other nanocomposites at high temperatures.

Atomic-scale imaging of wall-by-wall breakdown and concurrent transport measurements in multiwall carbon nanotubes

We report the atomic-scale imaging with concurrent transport measurements of the breakdown of individual multiwall carbon nanotubes inside a transmission electron microscope equipped with a piezomanipulator. We found unexpectedly three distinct breakdown sequences: namely, from the outermost wall inward, from the innermost wall outward, and alternatively between the innermost and the outmost walls. Remarkably, a significant amount of current drop was observed when an innermost wall is broken, proving unambiguously that every wall is conducting. Moreover, the breakdown of each wall in any sequence initiates in the middle of the nanotube, not at the contact, proving that the transport is not ballistic.

Role of NADP+-dependent isocitrate dehydrogenase (NADP+-ICDH) on cellular defence against oxidative injury by gamma-rays

PURPOSE

To investigate the regulation of NADPH-producing isocitrate dehydrogenase (ICDH) in cytosol (IDPc) and mitochondria (IDPm) upon gamma-ray irradiation, and the roles of IDPc and IDPm in the protection against cellular damage induced by gamma-ray irradiation.

MATERIALS AND METHODS

Changes of IDPc and IDPm proteins upon gamma-ray irradiation to NIH3T3 cells were analysed by immunoblotting. To increase or decrease the expression of IDPc or IDPm, NIH3T3 cells were stably transfected with mouse IDPc or IDPm cDNA in either the sense or the antisense direction. The transfected cells with either increased or decreased IDPc or IDPm were exposed to gamma-rays, and the levels of reactive oxygen species generation, protein oxidation and lipid peroxidation were measured.

RESULTS

Both IDPc and IDPm activities were induced by gamma-ray in NIH3T3 cells. Cells with decreased expression of IDPc or IDPm had elevated reactive oxygen species generation, lipid peroxidation and protein oxidation. Conversely, overproduction of IDPc or IDPm protein partially protected the cells from oxidative damage induced by gamma-ray irradiation.

CONCLUSIONS

The protective role of IDPc and IDPm against gamma-ray-induced cellular damage can be attributed to elevated NADPH, reducing equivalents needed for recycling reduced glutathione in the cytosol and mitochondria. Thus, a primary biological function of the ICDHs may be production of NADPH, which is a prerequisite for some cellular defence systems against oxidative damage.

Effects of polychlorinated biphenyl 19 (2,2',6-trichlorobiphenyl) on contraction, Ca2+ transient, and Ca2+ current of cardiac myocytes

Polychlorinated biphenyls (PCBs) have been known as serious environmental pollutants, causing developmental delays, motor dysfunction, and decrease in brain dopamine level in humans and animals. We have investigated the effects of a PCB congener, 2,2',6-trichlorobiphenyl (PCB 19) on contractile force, Ca2+ transient, and L-type Ca2+ current (I(Ca,L)) in guinea pig ventricular myocytes stimulated at a rate of 0.25-0.33 Hz. PCB 19 decreased contractile force in a concentration-dependent manner. During the negative inotropic response, the action potential duration at 20% (APD20), 90% of repolarization (APD90), and the action potential amplitude (APA) were decreased concentration dependently: 30 microM PCB 19 reduced APD20, APD90 and APA by 36.7 +/- 3.5%, 22.6 +/- 3.9%, and 2.4 +/- 0.6%, respectively (n = 11, p < 0.01). PCB 19 30 microM decreased the Ca2+ transient and the I(Ca,L) by 46.8 +/- 1.8% (n = 9, p < 0.01) and 47.1 +/- 3.1% (n = 9, p < 0.01), respectively. The results suggest that PCB 19 decreased the Ca2+ transient through inhibition of L-type Ca2+ channels and that the decreased Ca2+ transient consequently caused a negative inotropic effect in cardiac myocytes.

Control of mitochondrial redox balance and cellular defense against oxidative damage by mitochondrial NADP+-dependent isocitrate dehydrogenase

Mitochondria are the major organelles that produce reactive oxygen species (ROS) and the main target of ROS-induced damage as observed in various pathological states including aging. Production of NADPH required for the regeneration of glutathione in the mitochondria is critical for scavenging mitochondrial ROS through glutathione reductase and peroxidase systems. We investigated the role of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm) in controlling the mitochondrial redox balance and subsequent cellular defense against oxidative damage. We demonstrate in this report that IDPm is induced by ROS and that decreased expression of IDPm markedly elevates the ROS generation, DNA fragmentation, lipid peroxidation, and concurrent mitochondrial damage with a significant reduction in ATP level. Conversely, overproduction of IDPm protein efficiently protected the cells from ROS-induced damage. The protective role of IDPm against oxidative damage may be attributed to increased levels of a reducing equivalent, NADPH, needed for regeneration of glutathione in the mitochondria. Our results strongly indicate that IDPm is a major NADPH producer in the mitochondria and thus plays a key role in cellular defense against oxidative stress-induced damage.

Role of protein kinase C in alpha(1)-adrenergic regulation of a(Na)(i) in guinea pig ventricular myocytes

We investigated the role of protein kinase C (PKC) in alpha(1)-adrenergic regulation of intracellular Na(+) activity (a(Na)(i)) in single guinea pig ventricular myocytes. a(Na)(i) and membrane potentials were measured with the Na(+)-sensitive indicator sodium-binding benzofuran isophthalate and conventional microelectrodes, respectively, at room temperature (24-26 degrees C) while myocytes were stimulated at a rate of 0.25-0.3 Hz. The PKC activator 4beta-phorbol 12-myristate 13-acetate (PMA) decreased a(Na)(i) in a concentration-dependent manner. PMA (100 nM) produced a maximal decrease in a(Na)(i) of 1.5 mM from 6.5 +/- 0.4 to 5.0 +/- 0.4 mM (means +/- SE, n = 12, P < 0.01). The PMA concentration required for a half-maximal decrease in a(Na)(i) was 0.46 +/- 0.13 nM (n = 3, P < 0.01). An inactive phorbol, 4alpha-phorbol 12-myristate 13-acetate, did not decrease a(Na)(i). The decrease caused by PMA could be blocked by the PKC inhibitors staurosporine and bisindolylmaleimide I (GF-109203X). Stimulation of the alpha(1)-adrenoceptor with 50 microM phenylephrine decreased a(Na)(i) from 6.1 +/- 0.3 to 4.6 +/- 0.3 mM (n = 11, P < 0.01). The decrease in a(Na)(i) produced by phenylephrine was blocked by pretreatment with staurosporine, GF-109203X, or PMA. The decrease in a(Na)(i) produced by PMA was not prevented by pretreatment with tetrodotoxin but was blocked by pretreatment with strophanthidin or high extracellular K(+) concentration. The results suggest that alpha(1)-adrenergic receptor activation results in a decrease in a(Na)(i) via PKC-induced stimulation of the Na(+)-K(+) pump in cardiac myocytes.

Identification and functional characterization of a novel, tissue-specific NAD(+)-dependent isocitrate dehydrogenase beta subunit isoform

To understand the interactions and functional role of each of the three mitochondrial NAD(+)-dependent isocitrate dehydrogenase (IDH) subunits (alpha, beta, and gamma), we have characterized human cDNAs encoding two beta isoforms (beta(1) and beta(2)) and the gamma subunit. Analysis of deduced amino acid sequences revealed that beta(1) and beta(2) encode 349 and 354 amino acids, respectively, and the two isoforms only differ in the most carboxyl 28 amino acids. The gamma cDNA encodes 354 amino acids and is almost identical to monkey IDHgamma. Northern analyses revealed that the smaller beta(2) transcript (1.3 kilobases) is primarily expressed in heart and skeletal muscle, whereas the larger beta(1) mRNA (1.6 kilobases) is prevalent in nonmuscle tissues. Sequence analysis of the IDHbeta gene indicates that the difference in the C-terminal 28 amino acids between beta(1) and beta(2) proteins results from alternative splicing of a single transcript. Among the various combinations of human IDH subunits co-expressed in bacteria, alphabetagamma, alphabeta, and alphagamma combinations exhibited significant amounts of IDH activity, whereas subunits produced alone and betagamma showed no detectable activity. These data suggest that the alpha is the catalytic subunit and that at least one of the other two subunits plays an essential supporting role for activity. Substitution of beta(1) with beta(2) in the co-expression system lowered the pH optimum for IDH activity from 8.0 to 7.6. This difference in optimal pH was analogous to what was observed in mouse kidney and brain (beta(1) prevalent; optimal pH 8.0) versus heart (beta(2) prevalent; pH 7.6) mitochondria. Experiments with a specially designed splicing reporter construct stably transfected into HT1080 cells indicate that acidic conditions favor a splicing pattern responsible for the muscle- and heart-specific beta(2) isoform. Taken together, these data indicate a regulatory role of IDHbeta isoforms in determining the pH optimum for IDH activity through the tissue-specific alternative splicing.

Blockade of HERG channels expressed in Xenopus oocytes by external H+

We have investigated the effect of external H+ concentration ([H+]o) on the human-ether-a-go-go-related gene (HERG) current (IHERG), the molecular equivalent of the cardiac delayed rectifier potassium current (IKr), expressed in Xenopus oocytes, using the two-microelectrode voltage-clamp technique. When [H+]o was increased, the amplitude of the IHERG elicited by depolarization decreased, and the rate of current decay on repolarization was accelerated. The activation curve shifted to a more positive potential at lower external pH (pHo) values (the potential required for half-maximum activation, V1/2, was: -41.8 mV, -38.0 mV, -33.7 mV, -26.7 mV in pHo 8.0, 7.0, 6.6, 6.2, respectively). The maximum conductance (gmax) was also affected by [H+]o: a reduction of 7.9%, 14.6%, and 22.8% was effected by decreasing pHo from 8.0 to 7.0, 6.6, and 6.2, respectively. We then tested whether this pH effect was affected by the external Ca2+ concentration, which is also known to block HERG channels. When the extracellular Ca2+ concentration was increased from 0.5 mM to 5 mM, the shift in V1/2 caused by increasing [H+]o was attenuated, suggesting that these two ions compete for the same binding site. On the other hand, the decrease in gmax caused by increasing [H+]o was not significantly affected by changing external Ca2+ levels. The results indicate that HERG channels are inhibited by [H+]o by two different mechanisms: voltage-dependent blockade (shift of V1/2) and the decrease in gmax. With respect to the voltage-dependent blockade, the interaction between H+ and Ca2+ is competitive, whereas for the decreasing gmax, their interaction is non-competitive.