Biomedical subjects
Publications and source records attributed to M Shinkai.
We experienced the case of left atrial myxoma originating from posterior leaflet mitral valve. Mitral valve repair was performed in that case, because of the presence mitral leaflet defect due to removal of the myxoma. Transesophageal echocardiography was a useful tool for perioperative evaluation of the mitral valve and precise localization of the origin of the myxoma.
Ras is known to possess multiple cellular targets including Raf-1. Here, we measured both direct binding of various H-Ras mutants to two representative mammalian Ras targets, Raf-1 and B-Raf, and the activity of the mutants to stimulate Raf-1 and B-Raf, and analysed the difference in their Ras-interaction mechanisms. B-Raf was shown to share almost the same H-Ras binding-specificity with Raf-1 by examining binding of the H-Ras mutants to Raf-1 and B-Raf in the yeast two-hybrid and in vitro binding assays. Mutants, Y32F, A59E, and V45E bound to Raf-1 in Sf9 cells coexpressing them, but failed to activate Raf-1. On the other hand, Y32F activated B-Raf in a cell-free system which consisted of rat brain cytosol and recombinant MEK. These results suggest that there is a subtle structural difference in requirements for the interaction of Ras with Raf-1 and B-Raf.
B-Raf is regulated by Ras protein and acts as a mitogen-activated protein (MAP) kinase kinase kinase in PC12 cells and brain. Ras protein undergoes a series of post-translational modifications on its C-terminal CAAX motif, and the modifications are critical for its function. To elucidate the role of the post-translational modifications in interaction with, and activation of, B-Raf, we have analyzed a direct association between H-Ras and B-Raf, and constructed an in vitro system for B-Raf activation by H-Ras. By using methods based on inhibition of yeast adenylyl cyclase or RasGAP activity and by in vitro binding assays, we have shown that the segment of B-Raf corresponding to amino acid 1-326 binds directly to H-Ras with a dissociation constant (Kd) comparable to that of Raf-1 and that the binding is not significantly affected by the post-translational modifications. However, when the activity of B-Raf to stimulate MAP kinase was measured by using a cell-free system derived from rat brain cytosol, we observed that the unmodified form of H-Ras possesses an almost negligible activity to activate B-Raf in vitro compared to the fully modified form. H-RasSer-181,184 mutant, which was farnesylated but not palmitoylated, was equally active as the fully modified form. These results indicate that the post-translational modifications, especially farnesylation, are required for H-Ras to activate B-Raf even though they have no apparent effect on the binding properties of H-Ras to B-Raf.
A combined study of anterograde axonal degeneration and Golgi electron microscopic technique was designed to examine the distribution and density of axon terminals from the mediodorsal thalamic nucleus (MD) over layer III pyramidal cells in the prelimbic cortex of the rat. The reconstructive analysis of serial ultrathin sections of gold-toned apical and basal dendrites of layer III pyramidal cells showed that degenerating thalamocortical axon terminals from MD formed asymmetrical synaptic contacts predominantly with dendritic spines of the identified basal dendrites as well as apical dendrites. There was little difference in the numerical density of thalamocortical synapses from MD per unit length of both apical and basal dendrites.
To investigate the role of antiviral drug resistance in cytomegalovirus (CMV) disease progression, CMV cultured from an AIDS patient who developed progressive CMV disease despite continual anti- CMV treatment was characterized. In 7 CMV isolates, 1 ganciclovir-resistant strain predominated. Ganciclovir-resistant CMV, containing a UL97 mutation, was cultured from blood and urine before clinical indication of CMV central nervous system (CNS) disease, suggesting that the development of ganciclovir resistance preceded the dissemination of CMV to the CNS. Quantitative competitive polymerase chain reaction indicated that the isolation of ganciclovir-resistant CMV was concurrent with increased CMV DNA in plasma. The results suggest that antiviral resistance should be considered when selecting therapy for CMV CNS disease that develops in patients receiving treatment for CMV retinitis. In addition, plasma CMV DNA in AIDS patients receiving anti-CMV therapy may be a useful marker of disease progression and antiviral resistance.
'Magnetite cationic liposomes (MCL)' were developed as a means to generate intracellular hyperthermia. Affinity of the MCL to glioma cells was ten times higher than that of magnetite 'neutral' liposomes due to the electrostatic interaction based on the positive charge of the MCL. Heat generation of the MCL was studied using agar phantoms and small pellets of rat glioma cells. When a high-frequency magnetic field, 118 kHz, 384 Oe was applied to glioma cells in the presence of MCL, the glioma cell pellet of 80 microl (5.4 mm in diameter) was heated to over 43 degrees C and all the cells died after 40 min irradiation owing to the hyperthermic effect. The terminal temperature of the cell pellet was proportional to the pellet volume when other parameters were constant. It thus appears that the MCL can heat a tumor of more than 80 microl in volume to above 42 degrees C.
The longitudinal muscle of guinea-pig ileum was used as a test tissue. Progressive (up to 70 min) treatment with phenoxybenzamine (10(-6) M) inhibited progressively the response to histamine and progressively decreased the density of histamine H1-receptors. However, the 90 min treatment has no further significant inhibitory effect on the contractile response and did not decrease the density of the receptors. These results suggest that phenoxybenzamine discriminates between two distinct populations of H1-receptors. Furthermore, it was found that the presence of GTP gamma-S made some populations of H1-receptors resistant to phenoxybenzamine and facilitated an interaction of mepyramine with H1-receptors.
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A case of cardiac herniation following left intrapericardial pneumonectomy after induction chemoradiotherapy has been presented. Curative resection after induction chemoradiotherapy for central bronchogenic cancer may require intrapericardial pneumonectomy. Cardiac herniation through the pericardial defect is a fatal complication after a pneumonectomy unless pericardial repair should be done immediately. Closure of the pericardial defect with prosthetic patch, regardless of defect size, is always necessary for the prevention of the cardiac herniation following intrapericardial pneumonectomy after induction chemoradiotherapy.
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A 46-year old man, who had a history of right pneumonectomy for pulmonary tuberculosis 28 years ago, was referred to our hospital for surgical treatment of contralateral pneumothorax. The patient underwent multiple excisions of bullae and parietal pleurectomy through the median sternotomy in order to save pulmonary function. The postoperative course was satisfactory as he could maintain preoperative pulmonary function. He returned to his work soon. We consider that the median sternotomy would be the most useful approach to save pulmonary function of patients who plan to undergo surgical treatment of contralateral pneumothorax after pneumonectomy.
The patient was a 59-year-old man with a 5-month history of cough, difficulty breathing, and palpitations while working. Initial examination at the internal medicine department of our hospital in August 1992 revealed a mass in the left side of the neck, and he was admitted for further examination and treatment. Preoperative investigations revealed a cystic lesion extending from the left neck area to the mediastinum. The mass was resected on August 13, 1992. Based on the intraoperative findings and postoperative histological examination, a diagnosis of thoracic duct cyst was made. The postoperative course was good and the patient was discharged after two weeks. This is extremely rare case, and the Trap door surgical approach proved useful for resection.
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Ultrastructure of axon terminals projecting to the anterovetral thalamic nucleus (AV) from the reticular thalamic nucleus (RTN) of the rat was studied by using the anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). Anterogradely labeled fibers were distributed in ventral and caudal parts in AV following WGA-HRP injections into the medial part of rostral RTN, whereas labelings were found in the anterodorsal thalamic nucleus (AD) and dorsal part of AV following injections into the dorsal part of rostral RTN. The main labeled terminals were small to medium in size, containing pleomorphic vesicles, and made symmetrical contacts on wide range of neuronal surfaces, including cell bodies, dendritic shafts and their spines. Majority of these terminals made a single synaptic contact, whereas some labeled terminals had two synaptic contacts on two different postsynaptic profiles, such as on both soma and large dendrite, on both soma and small dendrite, on both soma and dendritic spine, and on both large and small dendrites.
A combined study of anterograde axonal degeneration and HRP retrograde labeling has shown that there exist monosynaptic connections between afferent fibers from the mediodorsal thalamic nucleus (MD) and callosal cells in the prelimbic cortex of the rat. Degenerating axon terminals from MD made asymmetrical synaptic contacts with dendritic spines from apical dendrites of layer III pyramidal cells that were retrogradely labeled with HRP after its injection into the prelimbic cortex contralateral to MD lesions.
Conservation of the structure and function of Ras proteins has been observed in a variety of eukaryotic organisms. However, the nature of their downstream effectors appears to be quite divergent; adenylyl cyclase and a protein kinase Raf-1, which do not share any structural homology with each other, are effectors of Ras in the budding yeast and in higher organisms, respectively. We show here that a protein kinase Byr2, which has been known to act downstream of Ras1 in a mating pheromone signal transduction system of Schizosaccharomyces pombe, binds directly to Ras proteins in a GTP-dependent manner. The region of Byr2 responsible for the Ras binding was mapped by a gene deletion analysis to its N-terminal segment of 206 amino acid residues, which does not possess any significant homology with the other effectors of Ras. The affinity of the Byr2 N terminus for Saccharomyces cerevisiae Ras2 was determined by measuring its activity to competitively inhibit Ras-dependent adenylyl cyclase activity and found to be comparable with those of yeast adenylyl cyclase and human Raf-1, with a dissociation constant (Kd) of about 1 nM. Furthermore, Byr2 inhibited a Ras GTPase-activating activity of Ira2, a S. cerevisiae homologue of neurofibromin. These results indicate that Byr2 is an immediate downstream target of Ras1 in S. pombe.
Twenty patients whose left internal thoracic artery (LITA) was anastomosed to the left anterior descending artery (LAD) underwent postoperative coronary angiography and Doppler ultrasound velocimetry. During angiography, the diameter of the LITA conduit was measured at three points: proximal, mid, and distal. The degree of left anterior descending artery stenosis proximal to the anastomotic site was evaluated by densitometry. The LITA flow velocity pattern was obtained at the three points to calculate the total, systolic, and diastolic flow volume. There were significant differences in the total LITA flow among the three points (proximal, 36.0 +/- 17.2 mL/min; mid, 29.9 +/- 15.2 mL/min; distal, 27.2 +/- 14.0 mL/min; p < 0.001 between the proximal and the mid or distal portions). The degree of left anterior descending artery stenosis affected the distal LITA flow and diameter (r = 0.823 and 0.811, respectively). There were significant differences in the systolic LITA flow among the three points (proximal, 13.2 +/- 6.5 mL/min; mid, 8.1 +/- 4.7 mL/min; distal, 5.6 +/- 3.4 mL/min; p < 0.001 between the proximal and the mid or distal portions). However, there was no statistically significant difference in the diastolic LITA flow among the three points (proximal, 22.9 +/- 11.0 mL/min; mid, 21.7 +/- 10.8 mL/min; distal, 21.6 +/- 10.8 mL/min). We conclude that a lower degree of LAD stenosis significantly reduces the LITA flow, inducing the string phenomenon. Additionally, during the diastolic phase, the LITA graft transports the blood primarily to the coronary artery but not to the side branches. Therefore, the steal phenomenon might not apply in the setting of an LITA graft.
1. Contractile responses and acetylcholine release evoked by nicotine and electrical field stimulation (EFS) were determined by isotonic transducer and radioimmunoassay, respectively. 2. Nicotine-induced contraction was reduced to 30% by nicotinic receptor antagonist, hexamethonium but was insensitive to tetrodotoxin. EFS-induced contraction was abolished by tetrodotoxin but was insensitive to hexamethonium. Replacement of external Na by choline completely abolished the contractile responses evoked by nicotine and EFS. 3. Both contractions evoked by nicotine and EFS were inhibited by omega-conotoxin GVIA, and inhibitory effects of the toxin were greater in low Ca concentrations. 4. In the condition that external Na or Ca is omitted from physiological solution, acetylcholine release evoked by nicotine was not observed. Nicotine-induced acetylcholine release was partially inhibited by omega-conotoxin but was insensitive to tetrodotoxin. 5. In conclusion, nicotine interacts with nicotinic receptors located on nerve terminals and produces transmitter release which depends on external Na through tetrodotoxin-insensitive mechanisms. It is suggested that voltage-dependent omega-conotoxin sensitive Ca channels are partially involved in the nicotine-induced transmitter release.