Yasunobu Hayabuchi

Hydrogen peroxide-induced vascular relaxation in porcine coronary arteries is mediated by Ca2+-activated K+ channels

SummaryHydrogen peroxide (H2O2) elicited concentration-dependent relaxation of endothelium-denuded rings of porcine coronary arteries. The relaxation induced by the H2O2 was markedly attenuated by 10μM 1H-[1,2,4]oxadiazolo [4,3,a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase, or by 100nM charybdotoxin, an inhibitor of large-conductance Ca2+-activated K+ (KCa) channels. A combination of the ODQ and charybdotoxin abolished the H2O2-induced relaxation. Pretreatment with 25 μM of an Rp stereoisomer of adenosine-3′,5′-cyclic monophosphothioate (Rp-cAMPS), 20μM glibenclamide, or 1mM 4-aminopyridine did not affect the vascular response to H2O2. The presence of catalase at 1000U/ml significantly attenuated the H2O2-induced relaxation. Exposure of cultured smooth muscle cells to H2O2 activated KCa channels in a concentration-dependent manner in cell-attached patches. Pretreatment with catalase significantly inhibited the activation of KCa channels. Rp-cAMPS did not inhibit the H2O2-induced activation of KCa channels. The activation of KCa channels by H2O2 was markedly decreased in the presence of ODQ. However, even in the presence of ODQ, H2O2 activated KCa channels in a concentration-dependent manner. In inside-out patches, H2O2 significantly activated KCa channels through a process independent of cyclic guanosine 3′,5′-monophosphate (cGMP). In conclusion, H2O2 elicits vascular relaxation due to activation of KCa channels, which is mediated partly by a direct action on the channel and partly by activation of soluble guanylate cyclase, resulting in the generation of cGMP.

Endothelium-derived hyperpolarizing factor activates Ca2+-activated K+ channels in porcine coronary artery smooth muscle cells.

Although endothelium-derived hyperpolarizing factor (EDHF) activity has been demonstrated in arteries from various species, EDHF has not been chemically identified, nor its mechanism of action characterized. To elucidate this mechanism, we tested the effect of EDHF on large-conductance Ca2+-activated K+ (K(Ca)) channels in porcine coronary artery smooth muscle cells. By using a patch-clamp technique, single-channel currents were recorded in cultured smooth muscle cells; the organ bath also contained a strip of porcine coronary with endothelium, which served as the source of endothelium-derived relaxing factor(s) including EDHF. Exposure of endothelium to 10(-6) M bradykinin activated K(Ca) channels in cultured smooth muscle cells in cell-attached patches. When the experiment was performed in the presence of 10 microM indomethacin and 30 microM N(G)-nitro-L-arginine (L-NNA), which block the generation of prostaglandin I2 (PGI2) and NO, respectively, K(Ca) channel activity was stimulated by bradykinin, indicating the direct involvement of EDHF in K(Ca) channel stimulation. Neither 10 microM methylene blue nor 25 microM Rp-cAMPS inhibited bradykinin-induced K(Ca) channel activity. In inside-out patches, the addition of bradykinin to the solution was without effect on K(Ca) channel activation. However, in the presence of 0.5 mM guanosine triphosphate (GTP) and 1.0 mM adenosine triphosphate (ATP) in the bath solution, K(Ca) channels was activated by bradykinin. In outside-out patches, the addition of bradykinin also increased K(Ca) channel activity, when GTP and ATP were added to the pipette solution. The addition of GDP-beta-S (100 microM) in the cytosolic solution completely blocked the activation K(Ca) channels induced by bradykinin in inside-out and outside-out patches. Pretreatment with 30 microM quinacrine, a phospholipase A2 inhibitor, or 3 microM 17-octadecynoic acid (17-ODYA), a cytochrome P450 inhibitor, in addition to indomethacin and L-NNA, abolished bradykinin-stimulated K(Ca) channel activity in cell-attached patches. Both 14,15-epoxyeicosatrienoic acid (EET) and 11,12-EET increased the open probabilities of K(Ca) channels in cell-attached patches. These results suggest that EDHF, released from endothelial cells in response to bradykinin, hyperpolarizes smooth muscle cells by opening K(Ca) channels. Furthermore, our data suggest that EDHF is an endothelium-derived cytochrome P450 metabolite of arachidonic acid. The effect of EDHF on K(Ca) channels is not associated with an increase of cAMP and cGMP. The activation of K(Ca) channels appears to be due to the activation of GTP-binding protein.

Plasma Levels of Natriuretic Peptide and Echocardiographic Parameters in Patients with Duchenne's Progressive Muscular Dystrophy

We investigated the relationship between plasma atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) levels and systolic and diastolic cardiac function, determined by echocardiography, in 63 patients with Duchennes progressive muscular dystrophy (DMD) (age range 8-21 years). The relationship between shortening fraction of the left ventricle and ANP and BNP levels was curvilinear rather than linear: When the shortening fraction was >15%, increases in ANP and BNP levels were minimal. However, if the shortening fraction was <15%, both natriuretic peptide levels increased dramatically. Stepwise regression analysis revealed that only the deceleration time of the early diastolic filling wave predicted plasma BNP concentration among various diastolic echocardiographic parameters determined by mitral flow. Three patients died of cardiac dysfunction during a 2-year follow-up period. These patients had a severely decreased deceleration time (<65% of normal) in association with increases in both natriuretic peptide levels. In conclusion, plasma ANP and BNP levels are not sensitive markers for the early detection of cardiac systolic dysfunction in patients with DMD. However, in patients with systolic dysfunction, an increase in the concentrations of these peptides, associated with a decrease in the deceleration time of early diastolic filling, suggests poor prognosis.

Hyperuricaemia in cyanotic congenital heart disease

This study examines the exacerbating factors of hyeruricaemia in patients with cyanotic congenital heart disease (CCHD). We studied 59 CCHD patients aged 1 month-30 years. The following variables were assessed: serum uric acid levels, red blood cell count, haemoglobin, hematocrit, partial oxygen pressure and arterial oxygen saturation. Uric acid excretion and renal function were also measured in ten patients with serum levels of uric acid greater than 8 mg/dl (hyperuricaemia group). Serum uric acid level correlated significantly with age and severity of polycythaemia. However, it did not correlate with partial oxygen pressure or arterial oxygen saturation. Uric acid excretion was measured in hyperuricaemia group. Urinary uric acid excretion (24 h) was within normal limits in infants but markedly lower in patients over 15 years of age. The aetiology of hyperuricaemia and decreased uric acid fractional excretion and clearance in infants appears to be secondary to diminished excretion of uric acid in concert with uric acid overproduction. Hyperuricaemia in adolescents and adults with CCHD, however, results mainly from age-related impairment of uric acid excretion.

Effect of acidosis on Ca2+-activated K+ channels in cultured porcine coronary artery smooth muscle cells

Abstract Although acidosis induces vasodilation, the vascular responses mediated by large-conductance Ca2+-activated K+ (KCa) channels have not been investigated in coronary artery smooth muscle cells. We therefore investigated the response of porcine coronary arteries and smooth muscle cells to acidosis, as well as the role of KCa channels in the regulation of muscular tone. Acidosis (pH 7.3–6.8), produced by adding HCl to the extravascular solution, elicited concentration-dependent relaxation of precontracted, endothelium-denuded arterial rings. Glibenclamide (20 µM) significantly inhibited the vasodilatory response to acidosis (pH 7.3-6.8). Charybdotoxin (100 nM) was effective only at pH 6.9–6.8. When we exposed porcine coronary artery smooth muscle cells to a low-pH solution, KCa channel activity in cell-attached patches increased. However, pretreatment of these cells with 10 or 30 µM O, O′-bis(2-aminophenyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid tetrakis(acetoxymethyl)ester (BAPTA-AM), a Ca2+ chelator for which the cell membrane is permeable, abolished the H+-mediated activation of KCa channels in cell-attached patches. Under these circumstances H+ actually inhibited KCa channel activity. When inside-out patches were exposed to a [Ca2+] of 10–6 M [adjusted with ethyleneglycolbis(β-aminoethylester)-N,N,N′,N′-tetraacetic acid (EGTA) at pH 7.3], KCa channels were activated by H+ concentration dependently. However, when these patches were exposed to a [Ca2+] of 10–6 M adjusted with BAPTA at pH 7.3, H+ inhibited KCa channel activity. Extracellular acidosis had no significant direct effect on KCa channels, suggesting that extracellular H+ exerts its effects after transport into the cell, and that KCa channels are regulated by intracellular H+ and by cytosolic free Ca2+ modulated by acute acidosis. These results indicate that the modulation of KCa channel kinetics by acidosis plays an important role in the determination of membrane potential and, hence, coronary arterial tone.

Efficacy of interferons in treating children with chronic hepatitis C

Abstract Twenty-two children with chronic hepatitis serologically positive for hepatitis C virus (HCV) were treated with interferon-α (IFN-α). Liver biopsy showed chronic active hepatitis in 13 and chronic persistent hepatitis in 9 patients. A sustained clearance of HCV was observed in 8/22 children 12 months after the administration of IFN-α for 26 weeks, associated with normalization of HCV core antibody. Of these eight patients six had HCV genotype III and two HCV genotype II or IV. Hepatitis relapsed in seven other patients after completion of IFN-α with an increase in HCV core antibody titre, five with HCV genotype II, and two with HCV genotype III or IV. A second course of IFN-α suppressed the reactivation of HCV in all seven patients. Three of seven responders who relapsed after the first course remained negative for HCV RNA 12 months after their second course of IFN-α. However, the remaining four patients with HCV genotype II again relapsed after completing their second course of IFN-α. Seven children with the HCV genotype II resistant to IFN, including 8 weeks of IFN-β administration, and showed no significant reduction in HCV core antibody titre. Conclusion The genotype of HCV (III) and a reduction in the core antibody titre appear to be useful parameters for predicting the response to IFN-α therapy.

Echocardiographic evaluation of the development of aortic valve prolapse in supracristal ventricular septal defect

The development and timing of aortic weve prolapse (AoVP) and aortic regugitation (AR) was studied by two limensional echocardiography in 99 consecutive patients with supracristal ventricular septal defect (VSD). Thirty patients (30%) had aortic valve prolapse (VSD+AoVP group), and 31 patients (31%) had AoVP with AR (VSD+AoVP+AR group). In the VSD+AoVP group, AoVP was detected first by echocardiography at the age of 6.8±4.2 years (mea±SD). In the VSD+AoVP+AR group, the interval from detection of AoVP to the appearance of Al was 3.4±2.0 years. The configuration of the prolapsed aortic valve was echocardiographically classified into two types: teardrop type (small) prolapse and box type (large) prolapse. The frequency of tear-drop tyrolapse was not significantly different between VSD+AoVP and VSD+AoVP-AR groups (43% versus 32%, respectively), indicating that even minor AoVP can result, AR. Four infants (4%) had AoVP at the ages of 1, 5, 7, and 11 months, respectively. All infants had tear-drop type prolapse. Two infants developed AR by colour flow mapping at the ages of 3 and 11 months, and the interval from prolapse to AR was only 2 and 4 months, respectively.ConclusionAortic valce, involement can develop under the age of 1 year in supracristal VSD. Regular evaluation by two-dimensional echocardiography with colour flow mapping is important in the followup of children with supracristal VSD.

Assessment of systemic-pulmonary collateral arteries in children with cyanotic congenital heart disease using multidetector-row computed tomography: Comparison with conventional angiography

BACKGROUND The present study aimed to assess the feasibility of multidetector-row computed tomography (MDCT) for the evaluation of systemic-pulmonary collateral (SPC) arteries in children with congenital heart disease associated with reduced pulmonary blood flow. METHODS Forty-eight consecutive patients (mean age 9+/-5 months; range, 0-30 months) underwent MDCT angiography of the thorax with a 16-detector row scanner prior to cardiac catheterization and operation. Conventional angiographic findings were used as a gold standard for the detection of SPC vessels. Findings on CT angiograms, including CT scans, maximum intensity projections, and three-dimensional volume-rendered images, were used to evaluate depiction of SPC arteries. Quantification of measurements at the SPC artery diameter was evaluated independently on MDCT and conventional invasive angiography. RESULTS Among the 48 patients, 115 SPC arteries were identified with conventional angiography, and 94 SPC arteries were identified with MDCT. In 89 (77%) vessels, concordant findings were observed with both modalities, with adequate depiction in 53 vessels and suboptimal depiction in 36 vessels. In 26 (23%) vessels, MDCT was unable to identify SPC arteries. Further, CT angiography resulted in the false-positive identification of vessels in 5 cases. There was an excellent correlation between MDCT- and conventional angiography-based measurement of SPC vessel diameter (R(2)=0.83), although a systematic overestimation was observed with MDCT (bias 0.19+/-0.74 mm). CONCLUSIONS This study demonstrates that MDCT is a potentially useful tool, which may have implications for planning percutaneous interventions and surgical repair in the future.

Autonomic function in patients with Duchenne muscular dystrophy

Background:  Assessing autonomic function is important for patients with chronic heart failure, but the way that autonomic function changes in patients with Duchenne muscular dystrophy (DMD) and correlates with other clinical parameters during their young age is not clearly known.

PLASMA CONCENTRATIONS OF ATRIAL AND BRAIN NATRIURETIC PEPTIDES AND CYCLIC GUANOSINE MONOPHOSPHATE IN RESPONSE TO DOBUTAMINE INFUSION IN PATIENTS WITH SURGICALLY REPAIRED TETRALOGY OF FALLOT

Abstract. We examined the plasma concentrations of atrial and brain natriuretic peptides (ANP and BNP) and cyclic guanosine monophosphate (cGMP) during dobutamine infusion and their relationship with hemodynamic parameters in 14 patients with surgically repaired tetralogy of Fallot (TOF). Dobutamine was infused at an initial dose of 5 μg/kg/min and increased by 5 μg/kg/min up to 20 μg/kg/min. The plasma ANP, BNP, and cGMP concentrations were determined before infusion, at the end of each stage, and 15 minutes after discontinuing dobutamine infusion. The plasma concentrations of ANP, BNP, and cGMP were elevated in all patients before dobutamine infusion. The ANP, BNP, and cGMP concentrations decreased in 11 of the 14 patients during dobutamine infusion. In contrast, the plasma ANP and BNP concentrations increased in the remaining 3 patients without a change in the cGMP concentration. The right ventricular pressure and volume were significantly elevated in these patients. The plasma cGMP concentration correlated with the ANP concentration (r= 0.62, p < 0.01) but not the BNP concentration. The plasma ANP concentration during dobutamine infusion correlated with right ventricular systolic pressure (r= 0.71, p < 0.05), mean right atrial pressure (r= 0.29, p < 0.05), and mean pulmonary capillary wedge pressure (r= 0.32, p < 0.05). The BNP concentration correlated with right ventricular volume (r= 0.61, p < 0.05) and systolic pressure (r= 0.46, p < 0.05). In conclusion, rapid changes in ANP, BNP, and cGMP concentrations during dobutamine infusion reflect the changes in atrial and ventricle pressure and volume overload. In surgically repaired TOF, the ANP concentration is affected by right ventricular systolic pressure, right atrial pressure, and pulmonary capillary pressure. Furthermore, the BNP concentration reflects right ventricular pressure and volume overload.