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Biomedical subjects

M Kaibara

Publications and source records attributed to M Kaibara.

At least 37 records · Page 2Linked to original sources
PubMed1999

Regional and functional differences of 5-hydroxytryptamine-receptor subtypes in guinea pig stomach.

Functions and the presence of 5-hydroxytryptamine (5-HT) receptors in the fundus, corpus and antrum of the guinea pig stomach were examined by measuring contractile force and acetylcholine (ACh) release. Stimulation of the 5-HT1 receptor caused tetrodotoxin (TTX)-insensitive relaxations in the preparations from 3 regions. Stimulation of the 5-HT2 receptor caused TTX-insensitive contractions in the preparations of fundus and antrum. Stimulation of 5-HT3 receptors caused contractions that were sensitive to TTX and atropine and enhanced the outflow of [3H]ACh from preparations of only antrum. Stimulation of 5-HT4 receptors caused contractions of antral strips and decreased relaxations of corporal strips and enhanced the outflow of [3H]ACh from the preparations of both corpus and antrum. In the guinea pig stomach, the fundus possesses relaxant 5-HT1 receptor < contractile 5-HT2 receptors and caused the contractile response to 5-HT. The corpus possesses relaxant 5-HT1 receptors and relaxant receptors other than 5-HT1, 5-HT2, 5-HT3 and 5-HT4 receptors > contractile 5-HT4 receptor, and therefore 5-HT caused relaxations. The antrum possesses relaxant 5-HT1 receptor < contractile 5-HT2, 5-HT3 and 5-HT4 receptors, and thus 5-HT caused contractions.

Animals↗
PubMed1998

Cloning and tissue distribution of novel splice variants of the rat GABAB receptor.

We have identified two novel splice variants of the metabotropic gamma-aminobutyric acid receptor (GABABR1), designated GABABR1c and GABABR1d, when screening a rat cerebellum cDNA library. GABABR1c has an amino acid sequence identical to GABABR1b, a member of GABABR1 isoforms, and an additional 93-bp insertion that generates an additional 31-amino-acid sequence in the fifth transmembrane region of GABABR1b. Thus, GABABR1c may have a structural variation in the second extracellular loop and fifth transmembrane region. GABABR1d also has an amino acid sequence identical to GABABR1b and an additional insertion of 566 bp that generates a divergent amino acid sequence in the carboxylterminal end. Reverse-transcription polymerase chain reaction analysis showed that in various rat tissues GABABR1c mRNA was ubiquitously expressed and GABABR1d mRNA in forebrain, cerebellum, eye, kidney, and urinary bladder. GABABR1 isoforms may function not only in the central nervous system but also in various peripheral tissues.

Alternative Splicing↗
PubMed1998

Activation of inwardly rectifying K+ channels by GABA-B receptors expressed in Xenopus oocytes.

In Xenopus oocytes coinjected with poly(A)+ RNA derived from the rat cerebellum and cRNAs for the cloned G protein-gated inwardly rectifying K+ channel (GIRK), GIRK1 and GIRK2, the GABA-B agonist baclofen elicited inwardly rectifying K+ currents. The inward K+ currents elicited by baclofen were inhibited by the selective GABA-B antagonists 2-OH saclofen and CGP 35348, and by the GIRK inhibitor Ba2+. In contrast, baclofen caused no currents in oocytes injected with the cerebellar poly(A)+ RNA alone, the poly(A)+ RNA and cRNA for GIRK1 or GIRK2, or only cRNAs for GIRK1 and GIRK2. These findings indicate that GABA-B receptors in the rat cerebellum were functionally expressed in Xenopus oocytes and activated the cloned GIRKs composed of GIRK1 and GIRK2 as heteromultimers.

Animals↗
PubMed1998

Function of the rat calcitonin receptors, C1a and C1b, expressed in Xenopus oocytes.

The function of the cloned rat calcitonin receptors, C1a and C1b, was studied in Xenopus oocytes using the two-electrode voltage clamp method. In oocytes expressing the C1a receptors and the cystic fibrosis transmembrane conductance regulator (CFTR), C1a/ CFTR, application (30 sec) of either salmon calcitonin (sCT) or human calcitonin (hCT) activated currents through CFTR. In C1b/CFTR, sCT activated the currents, whereas hCT failed to elicit a response. The sCT induced currents in C1a/CFTR were similar in size to those in C1b/CFTR. Both the activation and the deactivation of sCT-induced currents were slower in C1a/ CFTR. In oocytes expressing C1a or C1b alone, application of relatively high concentrations of sCT induced small oscillatory inward currents. Application of hCT induced small inward currents in C1a alone, but failed to activate currents in C1b alone. These results demonstrate new insights into the signal transduction of calcitonin receptors.

Adenylyl Cyclases↗
PubMed1998

Atrial conduction curves in patients with and without atrial fibrillation.

In order to quantify underlying atrial conduction properties in patients with atrial fibrillation (AF) using clinical electrophysiology techniques, atrial conduction curves relating intra-atrial conduction times to extrastimulus prematurities during programmed atrial stimulation were drawn. Based on the presence or absence of AF episodes, 95 subjects were divided into 2 groups: control (n=42); and AF (n=53). During programmed stimulation introduced from the right atrial appendage, an atrial conduction curve was drawn for each patient. For most of the control subjects, when the extrastimulus prematurity was increased by 10-ms steps, the intra-atrial conduction times also increased gradually; the maximum stepwise prolongation in intra-atrial conduction time was 11.0+/-3.4 msec. For patients with AF, a 10-msec increase in extrastimulus prematurity often produced a sudden marked prolongation in the intra-atrial conduction time; the maximum stepwise prolongation of intra-atrial conduction time was 21.4+/-5.9 msec. In contrast to the gradual atrial conduction curves recorded in control subjects, the sudden prolongation of intra-atrial conduction time was remarkable on the curves obtained in patients with AF. Statistical significance was clearly established (p<0.0001). This difference could be related to differences in the underlying conduction properties in patients with and without AF.

Adult↗
PubMed1997

Unmasking of fast and slow atrioventricular nodal pathways by successful radiofrequency ablation of two accessory atrioventricular connections.

Electrophysiologic findings suggesting the coexistence of dual atrioventricular (AV) nodal pathways and accessory AV connections have been previously described. Anterograde conduction through the accessory pathway (AP) may preclude the diagnosis of AV nodal dual pathway physiology during atrial stimulation. This study reports on a patient with manifest Wolff-Parkinson-White syndrome with clinically documented paroxysmal atrial fibrillation, in whom dual AV nodal pathways were unmasked after successful radiofrequency ablation of two accessory AV connections. In spite of detailed investigation, fast and slow AV nodal pathways were not detected in the first electrophysiologic study 8 years before ablation, nor were they detected during preablation study because of exclusive anomalous anterograde conduction. The anterograde AP effective refractory period was shorter than that of the fast and slow AV nodal pathways, and was limited by atrial refractoriness at 190 ms. The present findings strongly suggest the necessity for a careful postablation eletrophysiologic study before and after isoproterenol administration with specific evaluation of AV nodal conduction. This is the first documented report on the finding of AV nodal dual pathway physiology and reentry after successful radiofrequency ablation of two APs. This finding may be of great therapeutic significance in light of the feasibility of slow pathway ablation also during a single session, had AV nodal reentry been induced in a sustained manner after ablation of the AP to prevent late recurrence of tachycardia.

Adult↗
PubMed1997

Run-down of the cardiac Ca2+ channel: characterization and restoration of channel activity by cytoplasmic factors.

Possible mechanisms for run-down in the Ca2+ channel, such as proteolysis or dephosphorylation of the channel, were examined in guinea-pig ventricular myocytes. The Ca2+ channel current, recorded in inside-out patches using a pipette solution containing 50 mM Ba2+ and 3 microM Bay K 8644, ran down with a mean survival time of 2.35 min. The survival time was not significantly affected by adenosine triphosphate (ATP) (3 mM), 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid (BAPTA) (2 mM), isoprenaline (l-5 microM), phosphate (l20 mM) and leupeptin (l0 microM). Stimulation of guanosine triphosphate (GTP)-binding proteins was also ineffective. The catalytic subunit of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA, 0.5-2 microM) slightly and transiently increased channel activity, but had minimal effects on the channel when applied after complete run-down. On the other hand, cytoplasm from the heart, skeletal muscle, brain and liver, but not kidney, induced channel activity. There was a positive correlation between NPo (the product of the number of channels N and the open probability Po) value before run-down and that after the application of cytoplasm, suggesting that the activity of once-active channels was restored ba the exogenous cytoplasm. The potency of cytoplasm in tissues in inducing channel activity was not related to PKA activity nor to the number of dihydropyridine binding sites. These results suggest that the run-down of the cardiac Ca2+ channel is not mediated by dephosphorylation or proteolysis of the channel, but involves other factor(s), possibly interaction of the channel protein with a cytoplasmic regulatory protein.

Adenosine Triphosphate↗
PubMed1997

Endothelial cells on plasma-treated segmented-polyurethane: adhesion strength, antithrombogenicity and cultivation in tubes.

When the surface of segmented-polyurethane (SPU), where endothelial cells are not capable of proliferating, is modified by plasma treatment, the adhesion and proliferation of bovine aortic endothelial cells (BAECs) can be drastically improved. The cells were capable of proliferating on the inner surface of a plasma-treated SPU-coated tube (length: 50 mm; inner diameter: 1.5 mm). When a steady flow shear stress of 9 Pa was applied to the cells proliferated on the modified SPU surface for 90 min, most cells did not detach from the surface. From an in vitro evaluation test of antithrombogenicity, the cell surface can be considered to provide an inert surface against thrombus formation and blood coagulation. From analyses of the plasma-treated SPU surface, it was suggested that the improvements in BAEC proliferation and adhesion after plasma treatment were due to the change in wettability of the surface. Data suggest that the plasma treatment would be useful for developing a small-calibre hybrid vascular graft.

Journal Article↗
PubMed1997

Rheological study of the dynamic process of fibrinolysis.

The dynamic process of fibrinolysis induced by tissue plasminogen activator was examined using a rheological technique. Change in a rheological parameter (logarithmic damping factor) of whole blood and platelet-free plasma during fibrinolysis was largely dependent on the initial concentration of tissue plasminogen activator. Addition of activated partial prothrombin time reagent allowed determination of the time both of onset and end of fibrinolysis without affecting the coagulation process. The changes in the clot structure of fibrin during fibrinolysis were observed with a scanning electron microscope and compared with the time-dependent behavior of the logarithmic damping factor. Differences in the logarithmic damping factor during fibrinolysis were evident in alteration of the network structure of clots. It will be shown that the present rheological technique is useful for examining the concentration dependence of fibrinolytic reagent on fibrinolysis as well as for monitoring the dynamic process of fibrinolysis.

Adult↗
PubMed1997

Stereotactic amygdalohippocampotomy and mesial temporal spikes.

PURPOSE: To investigate the mechanism of mesial temporal spike generation, we sought to determine whether amygdalohippocampotomy by radiofrequency lesions altered spike rates in patients with medically intractable temporal lobe epilepsy. METHODS: The subjects were 14 patients whose ictal semiology, ictal and interictal EEGs, and neuropsychological profile were compatible with seizure origin from MRI-demonstrated unilateral mesial temporal sclerosis. Mesial temporal spikes were recorded by a multicontact electrode line stereotactically placed in the temporal horn of the lateral ventricle. A recording and lesioning electrode was also stereotactically advanced to multiple amygdala and hippocampal targets. Several confluent (9 patients) or discrete (5 patients) radiofrequency lesions were made in the amygdala and anterior hippocampus. Scalp and invasive recordings were performed before lesioning, between each lesioning process, and for 48 postoperative h. RESULTS: As compared to prelesion recordings, no consistent change in anterior and total mesial temporal spike rates occurred intraoperatively or postoperatively. Postlesion: prelesion spike ratios failed to correlate with effectiveness of lesionectomy for seizure control. In contrast, complex partial seizures improved in 13 of 14 patients. CONCLUSIONS: Amygdala and hippocampal destructive lesions had no consistent effect on meisal temporal spike quantity, but reduced temporal lobe CPS in 13 of 14 patients. This dichotomy suggests that CPS may result from concerted epileptogenesis of the hippocampus, entorhinal cortex, and possibly the amygdala, while the entorhinal cortex alone can produce interictal spikes.

Adolescent↗
PubMed1996

Promotion and control of selective adhesion and proliferation of endothelial cells on polymer surface by carbon deposition.

The adhesion and proliferation of endothelial cells can be drastically improved when cultivated on a carbon-deposited polymer surface. When the surface of segmented polyurethane, in which endothelial cells are not capable of proliferating, is modified by carbon deposition, cell adhesion and proliferation occurred selectively on the carbon-deposited region. Carbon deposition to a tissue culture-treated polystyrene surface on which cells are capable of proliferating further promoted cell spreading and proliferation. Cell patterning on carbon-deposited segmented polyurethane was also attempted by controlling the direction or region of cell proliferation. Carbon deposition onto the polymer surface brought about a decrease in the water contact angle of the surface. Precoating fibronectin or laminin on the carbon-deposited polymer surface brought about cell adhesion and proliferation in the carbon-deposited region, but not in the non-carbon-deposited region. Our data suggest that promotion of cell proliferation on a carbon-deposited surface is probably due to selective adhesion of adhesive proteins to the surface.

Animals↗
PubMed1996

Involvement of protein kinase C in gamma-aminobutyric acid release from Xenopus oocytes injected with rat brain mRNA.

Involvement of protein kinase C (PKC) in the release of gamma-aminobutyric acid (GABA) was examined in Xenopus laevis oocytes injected with mRNA from rat cerebellum, as compared with findings in slices of rat cerebellum. The mRNA-injected oocytes preloaded with [3H]GABA showed spontaneous release of [3H]GABA, approximately 0.5% of GABA content per 1 min. Stimulation with either Ca2+ ionophore (A23187) or a high K+ concentration increased the release of [3H]GABA from slices of rat deep cerebellar nucleus and mRNA-injected oocytes but not from noninjected and water-injected oocytes. 12-O-Tetradecanoylphorbol 13-acetate (10-300 nM) but not 4alpha-phorbol 12,13-didecanoate (300 nM) potentiated the A23187-stimulated release of [3H]GABA from slices and from mRNA-injected oocytes, in a concentration-dependent manner. Thus, machinery associated with release processes of GABA can be expressed in oocytes by injecting rat cerebellar mRNA, and PKC participates in GABA release from the functionally expressed GABAergic nerve terminals.

Animals↗
PubMed1996

[Signal transduction system in cardiac cells].

The electrical excitation and conduction in the heart is due to ionic events via ion channels and gap junctions. Function of these channels and gap junctions is regulated by intracellular milieu, which is regulated by many kinds of receptors through intracellular second messengers i.e.; GTP binding proteins, protein kinases, Ca2+ concentrations, H+ concentration, cyclic nucleotides and triphosphate nucleotides. In this paper, we focus on signal transduction systems in cardiac myocytes. Subsequently, some of interactions between signal transduction systems are introduced.

Cyclic AMP↗
PubMed1995

In vitro evaluation of antithrombogenicity of hybrid-type vascular vessel models based on analysis of the mechanism of blood coagulation.

In vitro evaluation of antithrombogenicity of materials of artificial vascular vessels was carried out based on an analysis of the coagulation mechanism of blood. Coagulation of blood in tubes coated with endothelial cells (ECs) or segmented polyurethane (SPU) was measured by a rheological technique. Coagulation of blood in hybrid-type vascular vessel model tubes consisting of cultured ECs proliferated on carbon-deposited SPU was also examined. Coagulation of blood in these tubes occurred within 40 min, and appears to be due to the interaction between erythrocytes and a coagulant factor in plasma. From the in vitro evaluation test, when the time of onset of the coagulation of blood in contact with a surface of the artificial materials is longer than 20-39 min, the materials can be considered to provide an inert surface against thrombus formation and blood coagulation.

Adult↗
PubMed1995

Electrophysiological effects of MS-551 in humans: a class III antiarrhythmic agent.

To investigate the clinical effects of MS-551, a Class III antiarrhythmic agent, 11 patients underwent electrophysiological study. MS-551 was given intravenously as an initial dose of 0.2 or 0.3 mg/kg for 5 minutes followed by the continuous infusion at 0.2 or 0.3 mg/kg for 30 minutes, respectively, in all patients. The rate corrected QT interval increased significantly from 3 minutes after the beginning of MS-551 infusion. The sinus heart rate decreased significantly by 8% at 10 minutes after the drug administration (P < 0.025). Mean PR and QRS intervals, and blood pressure were not significantly affected by the drug. Mean PA, AH, and HV intervals during sinus rhythm were also not affected. The effective refractory periods (ERPs) of the atrium and ventricle were significantly prolonged by 13% from 202 +/- 24 ms to 231 +/- 26 ms (P < 0.0005), and by 7% from 238 +/- 11 ms to 257 +/- 13 ms (P < 0.002), respectively, by MS-551. The ERP of the atrioventricular node and sinoatrial nodal recovery time were not changed significantly by the drug. This is a report of the effects of MS-551 in humans. This agent could be useful for treatment of tachyarrhythmias by prolongation of ERPs of the atrium and ventricle without significant variations of blood pressure and intracardiac conduction times. It is noteworthy that MS-551 slightly but significantly decreased heart rate.

Aged↗
PubMed1995

Radiofrequency catheter ablation for atrioventricular node reentry tachycardia with multiple slow atrioventricular node pathways.

Catheter ablation was attempted in 2 patients with atrioventricular node reentry tachycardia which showed fast, intermediate and slow anterograde atrioventricular node pathways. Radiofrequency currents were applied within a restricted area of the tricuspid annulus between the His bundle and the ostium of the coronary sinus where presumed slow pathway potentials were identified. Elimination of both the intermediate and the slow pathways, with preservation of anterograde and retrograde fast pathway conduction, was achieved in both patients.

Aged↗