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Biomedical subjects

M Imai

Publications and source records attributed to M Imai.

At least 235 records · Page 13Linked to original sources
PubMed1994

Cell Ca2+ response to luminal vasopressin in cortical collecting tubule principal cells.

Although vasopressin V1 receptors have been shown to exist in both luminal and basolateral membranes of rabbit cortical collecting duct (CCD), exact cell types having V1 receptors remain unestablished. To identify the distribution of V1 receptor by cytoplasmic Ca2+ response, we utilized the confocal imaging system in the microperfused rabbit CCD. Basolateral application of arginine vasopressin (AVP) increased [Ca2+]i mainly in one group of cells which were not stained by fluorescein-isothiocyanate-conjugated peanut agglutinin. Luminal application of AVP increased [Ca2+]i in the same cells which responded to basolateral AVP. These findings provide evidence that V1 receptors, as defined by the [Ca2+]i response, exist in both luminal and basolateral membranes of the rabbit principal cell.

Animals↗
PubMed1994

Mechanisms of the hyperkalaemia caused by nafamostat mesilate: effects of its two metabolites on Na+ and K+ transport properties in the rabbit cortical collecting duct.

1. The present experiments were undertaken to determine the mechanism(s) of hyperkalaemia caused by nafamostat mesilate (NM), a serine-protease inhibitor. 2. We investigated the effects of luminal addition of two metabolites of NM, p-guanidinobenzoic acid (PGBA) and 6-amidino-2-naphthol (AN), on Na+ and K+ transport properties of the collecting duct (CD) cell in the isolated perfused cortical collecting duct (CCD) from rabbit kidneys, because these metabolites, but not NM, were mainly excreted into the urine. 3. Addition of PGBA at 10(-5) and 10(-4) M in the lumen resulted in a hyperpolarization of VA in parallel with increases in transepithelial resistance (RT) and fractional apical membrane resistance (fRA). PGBA added to the luminal perfusate at 10(-5) and 10(-4) M changed VA, RT and fRA in a dose-dependent manner. These effects were completely inhibited by pretreatment with luminal amiloride (50 microM). PGBA at 10(-6) M in the lumen had no effect on the electrical parameters. 4. Luminal addition of AN at 10(-4) M also caused the apical membrane to hyperpolarize in parallel with increases in RT and fRA. These effects were also completely inhibited by pretreatment with luminal amiloride (50 microM). AN at 10(-5) M in the lumen had no effect on the electrical parameters. 5. We conclude that two metabolites of NM, PGBA and AN, act on the apical membrane of the CD cell and inhibit the amiloride-sensitive Na+ conductance, resulting in an inhibition of K+ secretion. This direct action of these metabolites, rather than NM, on the CCD might contribute to the NM-induced hyperkalaemia.

Animals↗
PubMed1994

[Investigation of AZT susceptibility of sequential HIV-1 isolates from patients treated with ddI after long-term therapy with AZT].

AZT susceptibility of sequential 12 HIV-1 isolates was investigated by culture method. These isolate were obtained from three patients who had received AZT for at least 12 months and switched to ddI after they appeared to deteriorate clinically. Cultures of isolate from a patient before therapy with AZT or ddI did not show cytopathic effect (CPE) in the presence of 0.1 microM or 1.0 microM AZT. Culture of 2 isolates from two patients treated with AZT more than 6 months before switched to ddI therapy showed CPE in the presence of AZT and HIV-1 p24 antigen was detected by ELISA in the supernatants. Culture of 6 of 7 isolates from three patients treated with ddI after long-term therapy with AZT also showed CPE in the presence of 1.0 microM AZT and HIV-1 p24 antigen was detected. These results demonstrated that AZT-resistant variant was still a dominant population in the isolate from patients after 11 to 13 months of discontinuing AZT therapy.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Axial heterogeneity of potassium transport across hamster thick ascending limb of Henle's loop.

Functional significance of morphological heterogeneities along the thick ascending limb of Henle's loop of hamsters was explored by the in vitro microperfusion technique with special reference to K+ transport. The transmission electron microscopic study confirmed that there are two types of cells, with smooth surface (S-cell) and rough surface (R-cell), respectively, and that the former is abundant in the medullary thick ascending limb (MTAL), whereas the latter is in the cortical portion (CTAL). The electrophysiological study revealed that in both segments there are two cell populations, one having high basolateral and low apical membrane K+ conductances (HBC) and the other having low basolateral and high apical K+ conductances (LBC). Random cell puncture revealed that the ratios of HBC/LBC were 24/7 (77%/23%) in the MTAL and 7/22 (24%/76%) in the CTAL, suggesting that HBC corresponds to S-cell, whereas LBC corresponds to R-cell. Net K+ transport was determined in two segments by measuring K+ concentration in the collected and perfused fluid by ultramicroflame photometry. In all six tubules of MTAL, net K+ flux had a direction to reabsorption with a mean of 4.87 +/- 0.46 pmol.min-1.mm-1. In marked contrast, in all six tubules of CTAL, we observed K+ secretion with a mean of -3.81 +/- 0.49 pmol.min-1.mm-1. The transmural voltage was positive in both segments and was significantly higher in the CTAL (7.8 +/- 0.5 mV) than in the MTAL (2.5 +/- 0.2 mV). From these observations, we conclude that the S-cell corresponding to the HBC cell reabsorbs K+, whereas the R-cell corresponding to the LBC cell secrets K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Inhibition of amiloride-sensitive apical Na+ conductance by acetylcholine in rabbit cortical collecting duct perfused in vitro.

We examined effects of acetylcholine (ACh) on the electrical parameters and intracellular Ca2+ concentration ([Ca2+]i) in the isolated rabbit cortical collecting duct (CCD) perfused in vitro using the conventional microelectrode technique and microscopic fluorescence spectrophotometry. ACh (10(-8) to 10(-5) M) in the bath caused a positive deflection of the transepithelial voltage (VT) and an increase in [Ca2+]i. Carbachol also showed similar but smaller effects. The effects of ACh were antagonized by muscarinic receptor antagonists. ACh at 10(-6) M hyperpolarized the apical membrane voltage and increased the fractional resistance of the apical membrane of the collecting duct cells accompanied by a positive deflection of VT and an increase in transepithelial resistance, whereas it did not affect these parameters in the beta-intercalated cells. In the presence of 10(-5) M amiloride in the lumen, the effects of ACh were almost completely abolished. The ACh-induced increase in [Ca2+]i is accounted for by the release of Ca2+ from intracellular store and Ca2+ entry from the bath. In the absence of Ca2+ in the bath, the ACh-induced changes in electrophysiological parameters were significantly smaller than those observed in the presence of Ca2+. Both phorbol-12-myristate-13-acetate (PMA) and phorbol-12,13-dibutylate (PDBu), activators of protein kinase C (PKC), also inhibited the apical Na+ conductance. In the presence of PMA or PDBu in the bath, ACh did not show further inhibitory effect. 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of PKC, partially attenuated the effect of ACh. These observations indicate that ACh inhibits the apical Na+ conductance partly by both increasing [Ca2+]i and activating PKC. Such an action of ACh may partially explain its natriuretic effect.

Acetylcholine↗
PubMed1994

Complete atrioventricular block during left heart catheterization.

A 75-year-old male underwent cardiac catheterization for frequent ventricular premature contractions and reduced left ventricular function. ECG on admission showed complete right bundle branch block (RBBB) and left anterior hemiblock. Right heart catheterization was performed uneventfully, but complete atrioventricular block (CAVB) occurred suddenly when a pig-tail catheter was inserted into the left ventricle. Electrophysiological study identified this CAVB as HV block, and demonstrated HV prolongation in sinus rhythm. The coronary angiogram revealed no obstructive lesion or spasm with ergonovine. The reproducibility of the CAVB was demonstrated. The final CAVB developed and persisted for more than one week, requiring the implantation of a permanent pacemaker (DDD). Complete atrioventricular block induced during left heart catheterization is very rare. Pre-existing RBBB with left anterior or posterior hemiblock and reduced left ventricular function may be common factors in patients with this condition. Emergency pacing equipment should always be on-line when left heart catheterization is conducted in such patients.

Aged↗
PubMed1994

Regulation of Cl- conductance in the thin ascending limb of Henle's loop.

Characteristics of the ion transport of the ascending thin limb of Henle's loop (ATL) were reviewed with special reference to the regulatory mechanisms of the putative Cl- channel. The ATL is highly permeable to NaCl, moderately permeable to urea, and virtually impermeable to water. The Cl- permeability is extremely high, having saturation kinetics and being inhibited by halogens. The Cl- conductances exist in series in both apical and basolateral membranes. They are inhibited by anion transport inhibitors including DIDS, phloretin, and NPPB. The Cl- conductance is pH sensitive and activated by Ca2+. NEM exhibits dual action on this conductance: irreversible inhibition and reversible stimulation. This highly effective Cl- transport system is favorable for the operation of the countercurrent multiplication system in the renal medulla.

Animals↗
PubMed1994

[Fiberscopic intubation under general anesthesia for children with Goldenhar syndrome].

Goldenhar syndrome is characterised by an eye abnormality such as epibulbar dermoid and lipoma, associated with ear, mandibular, and/or vertebral anomalies. It is well documented that difficult intubation in patient with this syndrome may be expected because of mandibular hypoplasia and limitation of neck movement resulting from vertebral anomalies. We report anesthetic management of two children with Goldenhar syndrome, 9 and 14-year-old. By preoperative examination, two children were expected to be difficult in intubating trachea. We used our newly developed mask adapter which enabled us to perform fiberoptic bronchoscopy-aided tracheal intubation under general anesthesia under controlled ventilation. By using this adapter, under sevoflurane/nitrous oxide anesthesia with vecuronium, we could successfully intubate with a 6 mm spiral tube through the nostril without any major problems. Anesthesia and surgery went uneventfully, and no postoperative complications were noted. We confirmed that our newly developed mask adapter for fiberoptic bronchoscopy is as useful for children with difficult intubation as for adults.

Adolescent↗
PubMed1994

[A case of liver metastasis from bile duct cancer effectively treated with hepatic artery infusion chemotherapy].

We performed hepatic artery infusion chemotherapy (HAI) combined with 5-FU-MMC-EPIR for bile duct cancer metastasized to the liver. We report a case for which we obtained PR. The case was a 59-year-old woman, who was diagnosed to have multiple liver metastases with an increase of CEA and LDH after 6 months from absolute curative resection for middle bile duct cancer. The patient was catheterized into the proper hepatic artery through the right femoral artery, and 5-FU 500 mg qw, MMC 4 mg q2w, and EPIR 30 mg q4w were infused via a reservoir. Two months after the treatment was begun, CEA and LDH values became normal. At the same time, PR was obtained and was shown upon CT, which continued for 5 months. After an 8-month period during which the patient was an outpatient at PS-0, multiple bone metastases appeared, and the radiotherapy was combinedly utilized for each lesion. The side effect of this method was decrease of leukocytes and blood platelets, but it disappeared by discontinuing medication. The patient died two years after the first operation, a year and four months from the time HAI was begun. It was possible to continue this treatment with PS 1-2 on an outpatient basis until one month before the patient's death. We concluded that hepatic artery infusion chemotherapy is an effective therapeutic method.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

[Severe ascending aortic stenosis after one-stage repair of aortopulmonary window and interrupted aortic arch].

A 33-day-old girl was transferred to our hospital because of severe cyanosis and tachypnea. The diagnosis of aortopulmonary window and interrupted aortic arch was established by echocardiogram and cineangiocardiogram. Reconstruction of aortic arch by extended direct anastomosis and simple patch closure of aortopulmonary window were performed by means of profound hypothermia and circulatory arrest on 36 days of age. Her postoperative clinical course was uneventful, but at 2 months after operation, stenosis of the ascending aorta was noticed by echocardiographic examination. As her physical growth had been satisfactory, she was managed under close observation at outpatient clinic. At seven months after operations, she fell into progressive left heart failure, and emergency operation was carried out for the relief of stenosis of the ascending aorta, but she could not come off bypass. A stenosis of the ascending aorta is a fatal complication that may occur after one-stage repair of interrupted aortic arch with aortopulmonary window consisting of extended direct anastomosis and simple patch closure. We now consider that division of ascending aorta and pulmonary artery and repair of both of the defect is indispensable for the correction of aortopulmonary window, especially in neonate and small infant with this lesion associated with interrupted aortic arch.

Aorta↗
PubMed1994

Photopic electroretinogram implicit time in diabetic retinopathy.

Photopic electroretinograms (ERGs) elicited with red or white flashes of various intensities under a bright background light were recorded in 119 eyes of 77 diabetic patients and 19 normal control eyes. The implicit time and amplitude of photopic ERGs were analyzed in relation to the stage of diabetic retinopathy, ie, diabetic eyes without retinopathy, eyes with mild nonproliferative diabetic retinopathy (mild NPDR), moderate NPDR, preproliferative diabetic retinopathy (PPDR) and proliferative diabetic retinopathy (PDR). The implicit time was significantly delayed in eyes with moderate NPDR, PPDR and PDR relative to eyes with mild NPDR, eyes without retinopathy or normal eyes. The delay of implicit time significantly increased as the severity of retinopathy progressed from mild NPDR to PPDR. The amplitude was reduced in PPDR and PDR, while the correlation with the severity of retinopathy was not so significant as with the delay of implicit time. These findings suggest that the photopic ERG implicit time can be a good indicator for the objective evaluation of the severity of diabetic retinopathy ranging from mild NPDR to PPDR, where retinal laser photocoagulation should be considered.

Adult↗
PubMed1994

[Surgical treatment of supravalvular aortic stenosis].

In the last 14 years, 7 consecutive patients with supravalvular aortic stenosis (SVAS) underwent surgical treatment for SVAS and/or for associated lesions. There were 5 male and 2 female patients ranging in age from 3 months to 12 years. Six of them had associated other cardiac anomalies; two had severe multiple peripheral pulmonary stenoses (PPS) and one each had ventricular septal defect (VSD), valvular pulmonary stenosis, coarctation of aorta with patent ductus arteriosus (PDA), total anomalous pulmonary venous return (TAPVR) with pulmonary branch stenosis, PPS and left lower pulmonary venous obstruction. The type of SVAS were localized in all and 5 of them underwent successful surgical repair of SVAS (3 with extended aortoplasty and 2 with patch aortoplasty). In 2 patients with VSD or valvular pulmonary stenosis, associated cardiac anomalies and SVAS were repaired simultaneously. Four patients had undergone previous operations, which included repair of severe multiple PPS by extended peripheral pulmonary arterioplasty (case 4, 6), repair of coarctation of aorta and division of PDA (case 5), repair of TAPVR (Ia + IIa) and pulmonary branch stenosis (case 7). There was no operative death and one patient died late postoperatively (case 7) due to right heart failure in a follow up period of 3 to 14 years. In conclusion, it is important to select the appropriate surgical treatment according to the location and the severity of associated other cardiac anomalies as well as the severity of SVAS, and extended peripheral pulmonary arterioplasty is considered to be a recommended method for the relief of severe multiple PPS associated with SVAS.

Aorta↗
PubMed1994

Valve injury: a new complication of internal jugular vein cannulation.

The anatomic appearance and competency of internal jugular valves were investigated in both cadavers and surgical patients. In 20 cadavers, the internal jugular vein (IJV) was dissected and the appearance of the valves observed. In two adult patients, the movements of the valves were observed by endoscopic visualization using an intravascular fiberscope, ultrasound techniques, and invasive venography. Transvalvular pressure gradients were measured in 10 adult surgical patients to examine the competence of the jugular venous valve. Nineteen internal jugular valves obtained from the 20 cadavers were situated directly above the termination of the IJV in the inferior bulb and were usually bilateral. The remaining 21 valves could not be examined since they had been already dissected out for another anatomical studies. The valves in 16 of the subjects were bicuspid and semiluminar. Two valves had a single cusp. The opening and closing of the valve was visualized easily with both a fiberscope and real-time ultrasound technique. Eight patients with normal central pressure had competent valves during cough-induced transvalvular pressure gradients of 45.3 +/- 10.1 (mean +/- SD) mmHg. Four valves from two cadavers remained competent at 75.4 +/- 18.2 mmHg, but became incompetent at 5.6 +/- 4.8 mmHg after a hole was made with a 14-gauge needle. Our results indicate that the IJV valve is located 0.5-2.0 cm above the union of the subclavian vein and IJV, and plays an important role in preventing retrograde blood flow to the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

[Additional palliative operation and staged definitive operation for pulmonary atresia with intact ventricular septum].

Between 1981 and 1992, 38 consecutive patients underwent initial operation for pulmonary atresia with intact ventricular septum. Transpulmonary valvotomy using balloon occlusion of RV outflow was carried out in 24 patients at a mean age of 20 days. An additional Blalock-Taussig shunt was required in 4 patients early in the series. Based on a retrospective review on the patients early in the series, initial palliative procedure had been decided in conformity with the value of an index of RV development (RVDI) = RVEDV% x TVD% x RVODmm/BSAm2 x 10(-5), and recent 3 patients with RVDI < 0.35 and patent RV outflow underwent concomitant valvotomy and Blalock-Taussig shunt. Fourteen patients with muscular atresia of RV outflow or major sinusoidal coronary artery communication underwent Blalock-Taussig shunt. There were 1 operative and 3 late deaths and second Blalock-Taussig shunt was required in 6 patients. Definitive repair was carried out in 20 patients between 1985 and 1994. Fifteen patients with RVEDV > 30% of normal had biventricular repair (partial closure of ASD in 6) and 5 underwent Fontan type repair. In terms of the definitive procedures, when the RV.TV index (= RVEDV% x TVD% x 10(-4)) is greater than 0.4, complete repair should be performed. When the index is between 0.2 and 0.4, the atrial septal defect should only be partially closed when the outflow tract is reconstructed. In those cases with an index of less than 0.2, the Fontan procedure seems to be a procedure of choice.

Humans↗
PubMed1993

Loop and distal actions of a novel diuretic, M17055.

We investigated the mechanism of action of a novel 'high ceiling' diuretic, M17055, in in vivo clearance studies with anesthetized dogs during water diuresis and in vitro microperfusion studies of isolated rabbit renal tubules. In the clearance study, intravenous infusion of M17055 (1 mg/kg per h) decreased free water clearance and increased urinary excretion of Na+ and Cl- to a greater extent than did a maximum dose of furosemide (30 mg/kg per h). With the maximum dose of furosemide, an additional dose of M17055 or hydrochlorothiazide resulted in additional suppression of free water clearance. These results indicate that M17055 has some additional mechanisms of action in the distal nephron. In isolated rabbit cortical thick ascending limb of Henle's loop, M17055 applied to the lumen decreased the lumen positive transepithelial voltage at concentrations over 10(-6) M and suppressed the lumen-to-bath 36Cl- flux at 10(-5) M. In the connecting tubule, M17055 added to the lumen suppressed lumen negative transepithelial voltage in a concentration-dependent manner in a range from 10(-4) to 10(-3) M. The effect of M17055 on transepithelial voltage was also observed in the distal convoluted tubule and cortical collecting duct. Moreover, 10(-3) M of M17055 in the lumen significantly decreased the lumen-to-bath 22Na+ flux in the cortical collecting duct. From these observations, it appears that M17055 acts not only on the thick ascending limb of Henle's loop but also on the distal segments via inhibition of electrogenic Na+ transport.

Animals↗