Insulin-like growth factor-I inhibits rat arterial K(ATP) channels through pI 3-kinase.

Since, in addition to its growth-promoting actions, insulin-like growth factor-I (IGF-I) has rapid vasoactive actions, we investigated the effects of IGF-I on whole-cell ATP-sensitive K(+) (K(ATP)) currents of rat mesenteric arterial smooth muscle cells. IGF-I (10 or 30 nM) reduced K(ATP) currents activated by pinacidil or a membrane permeant cAMP analogue. Inhibition of phospholipase C, protein kinase C, protein kinase A, mitogen-activated protein kinase or mammalian target of rapamycin (mTOR) did not prevent the action of IGF-I. However, inhibition of K(ATP) currents by IGF-I was abolished by the tyrosine kinase inhibitor genistein or the phosphoinositide 3-kinase inhibitors, LY 294002 and wortmannin. Intracellular application of either phosphatidylinositol 4,5-bisphosphate (PIP(2)) or phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) increased the K(ATP) current activated by pinacidil and abolished the inhibitory effect of IGF-I. Thus, we show regulation of arterial K(ATP) channels by polyphosphoinositides and report for the first time that IGF-I inhibits these channels via a phosphoinositide 3-kinase-dependent pathway.

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 Duchenne's 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.

Cytologic features of desmoplastic infantile ganglioglioma: a report of two cases.

BACKGROUND: Desmoplastic infantile ganglioglioma (DIG) is a rare intracranial tumor of infancy, characterized by solid and cystic components, voluminous size and supratentorial location. Although its histologic features have been reported, there has been no cytologic description of the tumor. Cytologic findings on imprint and aspirated material from two cases of histologically verified DIG are discussed. CASES: A 12-month-old male with cutis marmorata telangiectatica congenita and a 44-month-old female with episodes of spasm were referred to our center. Radiologic examination revealed a large, cystic, supratentorial mass in both patients. The mass was surgically removed, and histology revealed prominent desmoplasia with a mixture of astroglial and neuronal cells. Cytologic findings on imprint material and the needle aspirates taken from the cystic area of the tumor revealed a few isolated or sheetlike arrangements of small cells positive for glial fibrillary acidic protein and a few large cells with abundant cytoplasm and prominent nucleoli, positive for neuronal marker. CONCLUSION: Although distinction between ganglioglioma and DIG may be difficult by cytology alone, with the characteristic clinical presentation and radiologic findings, the possibility of DIG should be kept in mind when the specimens contain both astroglial and neuronal elements.

Angiotensin II inhibits and alters kinetics of voltage-gated K(+) channels of rat arterial smooth muscle.

The vasoconstrictor angiotensin II (ANG II) inhibits several types of K(+) channels. We examined the inhibitory mechanism of ANG II on voltage-gated K(+) (K(V)) currents (I(K(V))) recorded from isolated rat arterial smooth muscle using patch-clamp techniques. Application of 100 nM ANG II accelerated the activation of I(K(V)) but also caused inactivation. These effects were abolished by the AT(1) receptor antagonist losartan. The protein kinase A (PKA) inhibitor Rp-cyclic 3',5'-hydrogen phosphothioate adenosine (100 microM) and an analog of diacylglycerol, 1,2-dioctanyoyl-rac-glycerol (2 microM), caused a significant reduction of I(K(V)). Furthermore, the combination of 5 microM PKA inhibitor peptide 5-24 (PKA-IP) and 100 microM protein kinase C (PKC) inhibitor peptide 19-27 (PKC-IP) prevented the inhibition by ANG II, although neither alone was effective. The ANG II effect seen in the presence of PKA-IP remained during addition of the Ca(2+)-dependent PKC inhibitor Gö6976 (1 microM) but was abolished in the presence of 40 microM PKC-epsilon translocation inhibitor peptide. These results demonstrate that ANG II inhibits K(V) channels through both activation of PKC-epsilon and inhibition of PKA.

Evidence for involvement of A-kinase anchoring protein in activation of rat arterial K(ATP) channels by protein kinase A.

1. We have investigated the possible role of A-kinase anchoring proteins (AKAPs) in protein kinase A (PKA) signalling to ATP-sensitive K+ (K(ATP)) channels of rat isolated mesenteric arterial smooth muscle cells using whole-cell patch clamp and peptides that inhibit PKA-AKAP binding. 2. Intracellular Ht31 peptide (20 microM), which inhibits the PKA-AKAP interaction, blocked K(ATP) current activation by either dibutyryl cAMP or calcitonin gene-related peptide. Ht31-proline (20 microM), which does not inhibit PKA binding to AKAP, did not block K(ATP) current activation. 3. Ht31 reduced K(ATP) current activated by pinacidil and also prevented its inhibition by Rp-cAMPS, effects consistent with Ht31 blocking steady-state K(ATP) channel activation by PKA. However, Ht31 did not prevent K(ATP) current activation by the catalytic subunit of PKA. 4. An antibody to the RII subunit of PKA showed localization of PKA near to the cell membrane. Our results provide evidence that both steady-state and receptor-driven activation of K(ATP) channels by PKA involve the localization of PKA by an AKAP.

Gliclazide produces high-affinity block of KATP channels in mouse isolated pancreatic beta cells but not rat heart or arterial smooth muscle cells.

AIMS/HYPOTHESIS: Sulphonylureas stimulate insulin secretion by closing ATP-sensitive potassium (KATP) channels in the pancreatic beta-cell membrane. KATP channels are also found in other tissues, including heart and smooth muscle, where they link cellular metabolism to electrical activity. The sulphonylurea gliclazide blocks recombinant beta-cell KATP channels (Kir6.2/SUR1) but not heart (Kir6.2/SUR2A) or smooth muscle (Kir6.2/SUR2B) KATP channels with high potency. In this study, we examined the specificity of gliclazide for the native (as opposed to recombinant) KATP channels in beta cells, heart and smooth muscle. METHODS: The action of the drug was studied by whole-cell current recordings of native KATP channels in isolated pancreatic beta-cells and myocytes from heart and smooth muscle. RESULTS: Gliclazide blocked whole-cell beta-cell KATP currents with an IC50 of 184 +/- 30 nmol/l (n = 6-10) but was much less effective in cardiac and smooth muscle (IC50s of 19.5 +/- 5.4 micromol/l (n = 6-12) and 37.9 +/- 1.0 micromol/l (n = 5-10), respectively). In all three tissues, the action of the drug on whole-cell KATP currents was rapidly reversible. In inside-out patches on beta-cells, gliclazide (1 micromol/l) produced a maximum of 66 +/- 13 % inhibition (n = 5), compared with more than 98 % block in the whole-cell configuration. CONCLUSION/INTERPRETATION: Gliclazide is a high-potency sulphonylurea which shows specificity for the pancreatic beta-cell KATP channel over heart and smooth muscle. In this respect, it differs from glibenclamide. The difference in the maximal block observed in the excised patch and whole-cell recordings from beta-cells, may be due to the absence of intracellular Mg-nucleotides in the excised patch experiments.

Angiotensin II inhibits rat arterial KATP channels by inhibiting steady-state protein kinase A activity and activating protein kinase Ce.

We used whole-cell patch clamp to investigate steady-state activation of ATP-sensitive K+ channels (KATP) of rat arterial smooth muscle by protein kinase A (PKA) and the pathway by which angiotensin II (Ang II) inhibits these channels. Rp-cAMPS, an inhibitor of PKA, did not affect KATP currents activated by pinacidil when the intracellular solution contained 0.1 mM ATP. However, when ATP was increased to 1.0 mM, inhibition of PKA reduced KATP current, while the phosphatase inhibitor calyculin A caused a small increase in current. Ang II (100 nM) inhibited KATP current activated by the K+ channel opener pinacidil. The degree of inhibition was greater with 1.0 mM than with 0.1 mM intracellular ATP. The effect of Ang II was abolished by the AT1 receptor antagonist losartan. The inhibition of KATP currents by Ang II was abolished by a combination of PKA inhibitor peptide 5-24 (5 microM) and PKC inhibitor peptide 19-27 (100 microM), while either alone caused only partial block of the effect. In the presence of PKA inhibitor peptide, the inhibitory effect of Ang II was unaffected by the PKC inhibitor Go 6976, which is selective for Ca2+-dependent isoforms of PKC, but was abolished by a selective peptide inhibitor of the translocation of the epsilon isoform of PKC. Our results indicate that KATP channels are activated by steady-state phosphorylation by PKA at normal intracellular ATP levels, and that Ang II inhibits the channels both through activation of PKCepsilon and inhibition of PKA.

Left ventricular wall motion velocities in healthy children measured by pulsed wave Doppler tissue echocardiography: normal values and relation to age and heart rate.

Left ventricular wall motion velocities were measured by pulsed wave Doppler tissue (PWDT) echocardiography in 131 healthy children (mean age 7.5 +/- 5.5 years) at the interventricular septum and the posterior wall in the left ventricular short-axis view, and at the interventricular septum and the lateral wall in the 4-chamber view. The systolic wave (Sw) consisted of 2 components, and the difference between the 2 components was greater in the lateral wall than in the other walls. The peak early diastolic wave (Ew) velocity was also highest in the lateral wall. Most variables during systole correlated with age. The ratio of peak atrial systolic wave (Aw) velocity to peak Ew velocity (Aw/Ew) correlated with heart rate. The Aw/Ew in each wall correlated with the ratio of late (A) to early (E) peak mitral flow, although regression slopes differed among different wall segments. In younger children with increased heart rates, the Aw/Ew ratio increased because the Ew velocity decreased, although the A/E ratio increased because of an increased A velocity. Normal values for the PWDT variables change with heart rate and age in the pediatric population. The data reported in this study can be used as normal values for left ventricular function for PWDT echocardiography.

Cyclic variation of integrated ultrasound backscatter in the left ventricle during the early neonatal period.

BACKGROUND: Significant changes in the contractility and histologic structure of the ventricular myocardium occur during the early neonatal period. Cyclic variation (CV) of ultrasonic integrated backscatter (IBS) reflects myocardial contractile performance. The aim of this study was to define normal values of and its serial changes in CV of IBS in the left ventricle of normal neonates. METHODS AND RESULTS: We recorded long-axis IBS images in 169 healthy neonates within 14 days after birth (mean 4.6 +/- 4.2 days) and in 84 infants and children (mean age 8.7 +/- 5.2 years). For each, we obtained CV of IBS in the interventricular septum (CV(IVS)) and the posterior wall (CV(PW)). In neonates, there was a significant linear correlation between CV and date after birth in measurements of both the interventricular septum and the posterior wall (r = 0.57 and 0. 60, respectively). In infants and children, there was no significant relation between age and CV(IVS) or CV(PW). In neonates >4 days after birth, the magnitude of CV(IVS) was not significantly different from that in infants or children. By contrast, the magnitude of CV(PW) was still significantly decreased in neonates >9 days after birth compared with that in infants and children (P <. 005). The ratio of CV(IVS) to CV(PW) (CV(IVS)/CV(PW)) was significantly higher in neonates than in infants and children (0.99 +/- 0.29 vs 0.80 +/- 0.22, P <.001). CONCLUSIONS: Both CV(IVS) and CV(PW) in neonates gradually increase after birth, indicating developmental maturation of the left ventricle. High values of CV(IVS)/CV(PW) might reflect the remnant of relatively high contractile performance in the right ventricle during fetal life.

Retrograde holodiastolic flow in the abdominal aorta detected by pulsed Doppler echocardiography in patients with Kawasaki disease.

UNLABELLED: Retrograde holodiastolic flow in the abdominal aorta (retrograde flow) detected by pulsed Doppler echocardiography is usually noted in patients with aortic regurgitation or patent ductus arteriosus. Similar abnormal flow often is present in patients with acute phase Kawasaki Disease (KD). In 21 patients with acute phase KD, 15 had a retrograde flow. Retrograde flow was recognised in only 3 of patients with acute infection (n = 31) and in no healthy controls (n = 10). The ratio of the time velocity integral for diastolic retrograde flow to that for antegrade flow (regurgitant fraction) was significantly greater in patients with KD (median value 23%) than in patients with acute infection (1%) or healthy individuals (1%) (P < 0.001 for both). Four patients with coronary arterial involvement (one with an aneurysm and three with transient dilation of the coronary arteries) had a greater regurgitant fraction than the 17 patients without coronary arterial involvement (median values: 31% versus 18%, P < 0.05). The C-reactive protein was increased for a longer period of time in patients with KD with a greater regurgitant fraction (P < 0.01). Plasma nitric oxide (NO) metabolite concentrations were significantly greater in patients with KD than in those with acute infection or in healthy controls (P < 0.001 for both). There was a positive correlation between plasma NO metabolite concentrations and the regurgitant fraction in patients with KD (r = 0.69). CONCLUSION: Retrograde flow in the abdominal aorta is increased in patients with Kawasaki disease. Further studies are needed to clarify the causal relationship between the abnormal flow and the overproduction of nitric oxide.

Diagnosis and natural history of isolated congenital pulmonary regurgitation in fetal life.

We describe a rare instance of isolated pulmonary regurgitation caused by a dysplastic pulmonary valve which was detected prenatally. Fetal echocardiography demonstrated severe pulmonary regurgitation, and progressive cardiomegaly because of right ventricular volume overload. After birth, conservative therapy was successful in alleviating the pulmonary vascular resistance, and the pulmonary regurgitation gradually decreased.

A new sensitive and specific combination of CD81/CD56/CD45 monoclonal antibodies for detecting circulating neuroblastoma cells in peripheral blood using flow cytometry.

PURPOSE: Intensive chemoradiotherapy followed by peripheral blood stem cell transplantation has been introduced to treat children with advanced neuroblastoma (NBL). Detection of NBL cells in peripheral blood (PB) is important to prevent reinfusion of NBL cells. Several immunologic methods have been proposed for detecting NBL cells in hematologic samples. The development of a sensitive and specific combination of monoclonal antibodies (MoAbs) for detecting small numbers of NBL cells in PB using flow cytometry remains an important challenge. METHODS: Twenty-one clinical samples from NBL tissues or smears containing NBL cells were examined for reactivity against CD81, CD56, and CD9 using an immunocytochemical technique. The expressions of CD81, CD56, CD9, and antihuman disialoganglioside GD2 MoAb (GD2) in five NBL cell lines were assayed by flow cytometry. For the evaluation of sensitivity, five NBL cell lines were added to normal PB and the detection level of the combination of CD81/CD56/CD45 MoAbs was compared with that of CD9/CD56/CD45 MoAbs (reported previously). One hundred thirty-three normal PB samples were examined to determine the sensitivity and specificity of this method. RESULTS: All NBL cell lines showed strong positivity with CD81 and CD56 MoAb. However, CD9 MoAb was weakly positive against the five NBL cell lines. GD2 MoAb reacted strongly with four NBL cell lines, although almost the entire cell population of the SK-N-SH NBL line failed to bind the GD2 MoAb. In vitro experiments using NBL cell lines demonstrated that tumor cells added to normal PB cells could be detected by flow cytometry using CD81/CD56/CD45 MoAbs even at a concentration of 0.005%. Through comparative studies, the combination of CD81/CD56/CD45 MoAbs was found to be more sensitive and specific than that of CD9/CD56/CD45 MoAbs for detecting small numbers of NBL cells using the above cell lines. CONCLUSIONS: Triple-color flow cytometric analysis using CD81/CD56/CD45 MoAbs is useful for detecting NBL cells in PB. Further studies testing this approach using samples of PB with NBL contamination are needed to test this approach in patients.

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.

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 microgram/kg/min and increased by 5 microgram/kg/min up to 20 microgram/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.

Age-related endothelium-dependent vascular relaxation in rat thoracic aorta in response to colforsin.

BACKGROUND: Colforsin, a novel water-soluble forskolin derivative, increases intracellular cyclic AMP by direct stimulation of adenylate cyclase and has strong positive inotropic and vasodilative effects. However, it is not known whether colforsin causes nitric oxide (NO) release and enhances endothelium-dependent vascular relaxation. METHODS: We studied NO production and relaxation on exposure to colforsin in thoracic aorta from rats aged 4, 12 and 60 weeks. RESULTS: When a low concentration of colforsin was added to a solution bathing ring segments of aorta from 12-week-old rats, relaxation was greater in the ring segments with intact endothelium than in those from which the endothelium had been removed. A high concentration of colforsin induced the same degree of relaxation of ring segments with or without endothelium, probably by a direct effect on vascular smooth muscle cells. Production of NO in response to colforsin by cultured endothelial cells from 12-week-old rat aorta was demonstrated by the electron paramagnetic resonance spin trapping method. A low concentration of colforsin relaxed aortic segments with intact endothelium from 4-week-old rats more than those from 12-week-old or 60-week-old rats. Reversal of relaxation by NG-nitro L-arginine, an NO synthesis inhibitor, was most significant in arteries from 4-week-old rats. Production of NO after exposure to colforsin was greater in aortic segments from 4-week-old rats than older rats, as detected by an NO-selective electrode. CONCLUSIONS: Colforsin induces vasodilation in part by releasing NO from the endothelium in rat thoracic aorta. In addition to a direct vasodilative effect on the vascular smooth muscle cells, an endothelium-dependent vasodilative effect is also important in younger arteries.

Usefulness of color kinesis imaging for evaluation of regional right ventricular wall motion in patients with surgically repaired tetralogy of Fallot.

We evaluated regional right ventricular wall motion during systole in patients with surgically repaired tetralogy of Fallot (TOF) using color kinesis imaging. Color kinesis images were obtained in a subcostal sagittal view from 19 patients with repaired TOF (TOF group), aged 3 to 5 years, and 20 age-matched normal subjects (control group). For regional wall motion analysis, the endocardial motion distance and the fractional area change (FAC) were calculated for 6 segments obtained from color kinesis images. The endocardial inward excursion distances and the FACs in the upper, middle, and lower posterior segments of the TOF group were significantly greater than those of the control group (p <0.01 for each segment). The upper anterior segment showed significantly reduced inward excursion distance and FAC in the TOF group than in the control group (p <0.01, both). The dyskinetic outward excursion distances of the middle and lower posterior segments were significantly lower in the TOF group than in the control group (p <0.01, both). In the upper and middle anterior segments, the endocardial outward excursion distances were significantly higher in the TOF group than in the control group (p <0.01 and 0.05). Correlation between right ventriculographic and color kinesis measurements was excellent (y = 1.14x - 1.30, r = 0.87 for the endocardial inward excursion, and y = 1.03x +/- 0.56, r = 0.91 for the FAC). In conclusion, color kinesis is a useful method for assessing regional right ventricular wall motion. Segmental analysis of color kinesis images provides accurate, automated, and quantitative diagnosis of regional right ventricular wall motion abnormalities in patients with surgically repaired TOF.

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.

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

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 7.3­6.8), 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 6.9­6.8. 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 10­6 M [adjusted with ethyleneglycolbis(ß-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 10­6 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.

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

Under ischemic conditions and during strenuous exercise, lactate concentrations increase in coronary artery smooth muscle cells. Although lactate causes pH-independent vasorelaxation, the mechanisms responsible for this effect are unclear. We investigated the effect of lactate on K+ channels in smooth muscle cells from porcine coronary arteries. Neutralized lactate (3-100 mm) induced vasorelaxation in ring segments of porcine coronary arteries precontracted with KCl in a dose-dependent manner. One millimolar tetraethylammonium (TEA), an inhibitor of Ca2+-activated K+ channels (KCa channels), reversed the lactate-induced relaxation, while 60 microM glibenclamide, an inhibitor of ATP-sensitive K+ channels (KATP channels), did not. In both inside-out and cell-attached patch clamp technique with cultured smooth muscle cells, the KCa channels were activated by lactate. In inside-out patches, lactate activated KCa channels, even under acidic conditions. This is in contrast to the effect of H+ which inactivated KCa channels. We conclude that vasodilation of porcine coronary arteries induced by lactate is, at least in part, mediated by activation of KCa channels. This effect may be self-protective by maintaining coronary blood flow during ischemia.

Cerebral infarction in a patient with congenital complete heart block.

Stokes-Adams attacks are fairly common in children with congenital complete heart block, but the occurrence of cerebral infarction is quite unusual. We present the case of a 13-year-old boy with congenital heart block and an embolic stroke involving the cerebral artery. Echocardiography revealed no valvular regurgitation, hypokinetic segments, mural thrombus, or myxoma. Electrocardiographic monitoring demonstrated good response of ventricular rate to exercise and no episodes of atrial or ventricular dysrhythmia. It is assumed that embolism occurred due to bradycardia.