Ken Yamaura

Metabotropic Glutamate Receptor Activation Enhances the Activities of Two Types of Ca2+-Activated K+Channels in Rat Hippocampal Astrocytes

The influence of activation of glutamate receptor (GluR) on outward K+ current in cultured neonate rat hippocampal astrocytes was investigated. Patch-clamp analysis of K+ channel currents in cultured astrocytes identified the existence of 71 ± 6 and 161 ± 11 pS single-channel K+ currents that were sensitive to changes in voltage and [Ca2+]i and blocked by external TEA but not by charybdotoxin, iberiotoxin, apamin, or 4-aminopyridine. Reverse transcriptase (RT)-PCR and Northern blot analysis revealed transcripts of the Ca2+-activated K+ channel (KCa) β4-subunit (β4) (KCNMB4) in cultured astrocytes. Expression of the metabotropic glutamate receptor (mGluR) subtypes mGluR1 and mGluR5 and the ionotropic glutamate receptor (iGluR) subtypes iGluR1 and iGluR4 were detected by RT-PCR and immunofluorescence analysis in cultured astrocytes. The mGluR agonistsl-glutamate and quisqualate increased the open state probability (NPo) of the 71 and 161 pS K+ channel currents that were prevented by the mGluR receptor antagonists 1-aminoindan-1,5-dicarboxylic acid orl-(+)-2-amino-3-phosphonopropionic acid and not by the iGluR antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate or CNQX. Activation of the two types of K+ channel currents by mGluR agonists was attenuated by pertussis toxin and by inhibition of phospholipase C (PLC) or cytochrome P450 arachidonate epoxygenase. These results indicate that brain astrocytes contain the KCNMB4 transcript and express two novel types of KCa channels that are gated by activation of a G-protein coupled metabotropic glutamate receptor functionally linked to PLC and cytochrome P450 arachidonate epoxygenase activity.

Propofol-induced Increase in Vascular Capacitance Is Due to Inhibition of Sympathetic Vasoconstrictive Activity

Background Venodilation is thought to be one of the mechanisms underlying propofol‐induced hypotension. The purpose of this study is to test two hypotheses: (1) propofol increases systemic vascular capacitance, and (2) the capacitance change produced by propofol is a result of an inhibition of sympathetic vasoconstrictor activity. Methods In 33 Wistar rats previously anesthetized with urethane and ketamine, vascular capacitance was examined before and after propofol infusion by measuring mean circulatory filling pressure (Pmcf). The P (mcf) was measured during a brief period of circulatory arrest produced by inflating an indwelling balloon in the right atrium. Rats were assigned into four groups: an intact group, a sympathetic nervous system (SNS)‐block group produced by hexamethonium infusion, a SNS‐block + noradrenaline (NA) group, and a hypovolemic group. The Pmcf was measured at a control state and 2 min after a bolus administration of 2, 10, and 20 mg/kg of propofol. Results The mean arterial pressure (MAP) was decreased by propofol dose‐dependently in intact, hypovolemic, and SNS‐block groups, but the decrease in MAP was less in the SNS‐block group (‐25%) than in the intact (‐50%) and hypovolemic (‐61%) groups. In the SNS‐block + NA group, MAP decreased only at 20 mg/kg of propofol (‐18%). The Pmcf decreased in intact and hypovolemic groups in a dose‐dependent fashion but was unchanged in the SNS‐block and SNS‐block + NA groups. Conclusions The results have provided two principal findings: (1) propofol decreases Pmcf dose‐dependently, and (2) the decrease in Pmcf by propofol is elicited only when the sympathetic nervous system is intact, suggesting that propofol increases systemic vascular capacitance as a result of an inhibition of sympathetic nervous system.

Contribution of epoxyeicosatrienoic acids to the hypoxia-induced activation of Ca2+-activated K+ channel current in cultured rat hippocampal astrocytes

Brief hypoxia differentially regulates the activities of Ca(2+)-activated K(+) channels (K(Ca)) in a variety of cell types. We investigated the effects of hypoxia (<2% O(2)) on K(Ca) channel currents and on the activities of cytochrome P450 2C11 epoxygenase (CYP epoxygenase) in cultured rat hippocampal astrocytes. Exposure of astrocytes to hypoxia enhanced macroscopic outward K(Ca) current, increased the open state probability (NPo) of 71 pS and 161 pS single-channel K(Ca) currents in cell-attached patches, but failed to increase the NPo of both the 71 pS and 161 pS K(Ca) channel currents recorded from excised inside-out patches. The hypoxia-induced enhancement of macroscopic K(Ca) current was attenuated by pretreatment with tetraethylammonium (TEA, 1 mM) or during recording using low-Ca(2+) external bath solution. Exposure of astrocytes to hypoxia was associated with generation of superoxide as detected by staining of cells with the intracellular superoxide detection probe hydroethidine (HE), attenuation of the hypoxia-induced activation of unitary K(Ca) channel currents by superoxide dismutation with tempol, and as quantitated by high-pressure liquid chromatography/fluorescence assay using HE as a probe. In cultured astrocytes in which endogenous CYP epoxygenase activity has been inhibited with either miconazole or N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MSPPOH) hypoxia failed to increase the NPo of both the 71 pS and 161 pS K(Ca) currents and generation of superoxide. Hypoxia increased the level of P450 epoxygenase protein and production of epoxyeicosatrienoic acids (EETs) from cultured astrocytes, as determined by immunohistochemical staining and LC/MS analysis, respectively. Exogenous 11,12-EET increased the NPo of both the 71 pS and 161 pS K(Ca) single-channel currents only in cell-attached but not in excised inside-out patches of cultured astrocytes. These findings indicate that hypoxia enhances the activities of two types of unitary K(Ca) currents in astrocytes by a mechanism that appears to involve CYP epoxygenase-dependent generation of superoxide and increased production or release of EETs.

The Effect of Superoxide Anion on Autoregulation of Cerebral Blood Flow

Background and Purpose— Recent studies have suggested that autoregulation of cerebral blood flow (CBF) is impaired after traumatic and ischemic brain injury. Given that the levels of superoxide anion (O2·−) are increased in these conditions, we postulate that O2·− contributes to the impairment of CBF autoregulation. Methods— CBF was monitored with laser Doppler flowmetry during increases in blood pressure. Results— During the control period, CBF was well autoregulated after the increase in mean arterial pressure (MAP) from 98±3 to 140±6 mm Hg. The autoregulation index (AI; &Dgr;CBF/&Dgr;MAP) averaged 0.25±0.02 (n=6). O2·− in the brain was then increased by subdural perfusion of xanthine/xanthine oxidase (different concentrations) and catalase. Low concentrations of O2·− decreased basal CBF by 10±1.6% but had no effect on autoregulation (AI, 0.19±0.02; n=6). Higher concentrations of O2·− (0.2 mmol/L xanthine and either 3 or 20 mU xanthine oxidase) increased basal CBF by 30±2% and 42±4%, respectively, and impaired autoregulation of CBF (AI, 0.55±0.03 and 0.76±0.02; n=6). Inclusion of superoxide dismutase in the O2·−-generating system restored autoregulation (AI, 0.28±0.05; n=6). Neither inhibition of NO synthase nor the addition of deferioxamine had any effect on the ability of higher concentrations of O2·− to impair autoregulation of CBF (AI, 0.65±0.07 and 0.72±0.05 respectively; n=6). O2·− also increased the activity of KCa channels in cerebral vascular smooth muscle cells (VSMCs; n=8). Conclusion— These results suggest that O2·− increases basal CBF and impairs autoregulation of CBF, likely through the activation of KCa channels in cerebral VSMCs.

Changes in body temperature during profound hypothermic cardiopulmonary bypass in adult patients undergoing aortic arch reconstruction

PurposeOur aim was to characterize changes in body temperatures during profound hypothermic cardiopulmonary bypass (CPB) conducted with the sternum opened.MethodsIn ten adult patients who underwent profound hypothermic (≪20°C) CPB for aortic arch reconstruction, pulmonary arterial temperature (PAT), nasopharyngeal temperature (NPT), forehead deep-tissue temperature (FHT), and urinary bladder temperature (UBT) were recorded every 1 min throughout the surgery. In addition, the CPB venous line temperature (CPBT), a reasonable indicator of mixed venous blood temperature during CPB and believed to best reflect core temperature during stabilized hypothermia on CPB, was recorded during the period of total CPB.ResultsPAT began to change immediately after the start of cooling or rewarming, closely matching the CPBT (r = 0.98). During either situation, the other four temperatures lagged behind PAT (P ≪ 0.05); however, NPT followed PAT more closely than the other three temperatures (P ≪ 0.05). During stabilized hypothermia, PAT, NPT, and FHT, but not UBT, closely matched the CPBT, with gradients of less than 0.5°C.ConclusionDuring induction of profound hypothermia and its reversal on total CPB with the heart in situ, a PA catheter thermistor, presumably because of its placement immediately behind the superior vena cava, would provide a reliable measure of the mixed venous blood temperature. During stabilized profound hypothermia, PAT, NPT, and FHT, but not UBT, serve as a reliable index of core temperature.

Removal of retained air during cardiac surgery with transesophageal echocardiography and capnography

STUDY OBJECTIVE To evaluate a new method for removal of retained air at the end of cardiopulmonary bypass (CPB) by end-tidal CO2 pressure (PETCO2) and pulmonary arterial pressure (PAP) monitoring, and transesophageal two-dimensional echocardiography (TEE). DESIGN Prospective study. SETTING Cardiac surgery unit at a university hospital. PATIENTS 36 ASA physical status I, II, III patients for open heart surgery. INTERVENTIONS The CPB reservoir was gradually raised to decrease venous drainage. Accordingly, the right heart began to receive the venous blood and eject it to the pulmonary artery. The vent existing in the left ventricle or the left atrium then collected any whole blood containing air bubbles that came from the pulmonary circulation. The air bubbles were confirmed by TEE to be removed and not to eject from the left ventricle to te systemic circulation. MEASUREMENTS AND MAIN RESULTS Levels of PETCO2, PaCO2, PAP, and the duration of the removal procedure were measured when a sufficient pulmonary circulation was established and the removal of retained air was considered to be satisfactorily accomplished by the absence of air bubbles, confirmed by TEE for more than 30 seconds. PETCO2 reached 28 +/- 4 mmHg during the removal of air, while PaCO2 reached 35 +/- 6 mmHg (p < 0.05). Mean PAP during removal of air reached 18 +/- 4 mmHg, which was approximately 90% of that before CPB. The duration time of removal of air was 9 +/- 2 min. CONCLUSIONS PETCO2 and PAP are useful indicators of pulmonary circulation during this procedure for removal of air. PETCO2 of 25 to 30 mmHg and PAP of 90% of the prebypass level have been found to be necessary for the removal of air. Our technique for removal of air using PETCO2, PAP, and TEE enables us to satisfactorily eliminate residual air.

Effects of olprinone, a new phosphodiesterase inhibitor, on gastric intramucosal acidosis and systemic inflammatory responses following hypothermic cardiopulmonary bypass

Background: Phosphodiesterase (PDE) III inhibitors have both an inotropic and a peripheral vasodilatory effect, and also inhibit the activation of macrophages. Thus a newly developed PDE III inhibitor, olprinone, could modify gastric intramucosal pH (pHi), systemic oxygen consumption, and systemic inflammatory responses in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB).

Recurrent ventricular tachyarrhythmias associated with QT prolongation following hydrofluoric acid burns.

BACKGROUND Some hydrofluoric acid burns appear initially as only a slight wound, but patients may show dramatic changes within several hours. The extent of such burns are directly related to the concentration, amount, and duration of exposure. CASE REPORT A 64-year-old man sustained 44% total body surface burns after exposure to 30% hydrofluoric acid. Approximately 5 h after injury, he developed recurrent ventricular tachycardia and ventricular fibrillation which occurred in conjunction with long QT syndrome. In this case, the occurrence of hypocalcemia and especially hypomagnesemia played an important role in the development of long QT syndrome.

Detection of retroperitoneal hemorrhage by transesophageal echocardiography during cardiac surgery.

PurposeTo present a case of massive retroperitoneal hemorrhage during cardiopulmonary bypass (CPB) which was detected using transesophageal echocardiography (TEE).Clinical featureA 50-yr-old man suffering from severe mitral regurgitation (MR) was admitted for mitral valvuloplasty. After the beginning of CPB, the volume in the reservoir was noticed to be gradually decreasing. Although venous cannulation had been properly performed, TEE showed an echo free space around the liver, the spleen and in front of the abdominal aorta showed intraabdominal hemorrhage. After cardiac surgery, emergency laparotomy revealed about 5,000 ml of blood in the retroperitoneal space probably as a result of femoral artery cannulation prior to CPB. Hemostasis was achieved, and the patient made complete cardiac and neurological recovery. Retrospective review of the TEE imaging revealed that the kidneys were surrounded by blood bilaterally confirming the diagnosis of retroperitoneal hemorrhage.ConclusionRetroperitoneal hemorrhage during CPB is rare, but may be lethal. Transesophageal echocardiography is a useful monitor not only to evaluate cardiac performance, but also to detect unexpected intraabdominal bleeding during cardiac surgery.RésuméObjectifPrésenter le cas d’une hémorragie rétropéritonéale massive pendant la circulation extracorporelle (CEC), détectée à l’aide de l’échocardiographie transoesophagienne (ETO).Éléments cliniquesUn homme de 50 ans, souffrant de régurgitation mitrale sévère, a été admis pour une valvuloplastie mitrale. Après le début de la CEC, on a noté que le volume du réservoir baissait graduellement. Bien qu’on ait correctement réalisé la mise en place d’une canule veineuse, l’ETO a montré un espace libre d’écho autour du foie, de la rate et, en avant de l’aorte abdominale, indiquant la présence d’une hémorragie intra-abdominale. Après la cardiochirurgie, la laparotomie d’urgence a révélé la présence d’environ 5 000 ml de sang dans l’espace rétropéritonéal, le résultat probable de l’introduction d’une canule dans l’artère fémorale avant la CEC. L’hémostase a été rétablie et le patient a connu une récupération cardiaque et neurologique complète. Létude rétrospective des images de l’ETO a révélé que les reins étaient bilatéralement entourés de sang, ce qui confirme le diagnostic d’hémorragie rétropéritonéale.ConclusionL’hémorragie rétropéritonéale est rare pendant la CEC, mais elle peut être fatale. L’échocardiographie transoesophagienne est un moniteur utile non seulement pour évaluer le rendement du coeur, mais aussi pour détecter des saignements intra-abdominaux inattendus pendant la cardiochirurgie.

Noninvasive assessment of left ventricular pressure–area relationship using transesophageal echocardiography and tonometry during cardiac and abdominal aortic surgery

PurposeThe purpose of this study was to noninvasively evaluate intraoperative left ventricular (LV) performance by an online pressure–area relationship using transesophageal echocardiography (TEE) and tonometry.MethodsIn study 1, LV pressure with a micromanometer catheter, LV cross-sectional area with TEE, direct radial pressure, and tonometric arterial pressure were simultaneously recorded in 5 patients (10 measurements) undergoing cardiac surgery. End-systolic elastance (E′es) was determined from pressure–area loops during inferior vena caval (IVC) occlusion. In study 2, in 16 patients undergoing repair of abdominal aortic aneurysm, LV performance (E′es; effective arterial load, E′a, and LV end-diastolic area, LV-EDA) was examined by noninvasive assessment of pressure–area loops using TEE and tonometry at aortic cross-clamping and unclamping.ResultsE′es by tonometric arterial pressure closely correlated with E′es by LV pressure (r = 0.92) in study 1. E′es at aortic clamping were not significantly different from those at unclamping. The clamping increased LV-EDA and E′a by approximately 13% and 44%, and the unclamping significantly decreased by 9% and 22%, respectively.ConclusionOur results demonstrated that online tonometric arterial pressure and LV area measured by automated border detection (ABD) of TEE might be used to calculate E′es to estimate LV contractility and allow the estimation of LV performance during aortic clamping and unclamping.