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Biomedical subjects

H Takai

Publications and source records attributed to H Takai.

At least 55 records · Page 3Linked to original sources
PubMed1995

The effect of AL0671, a novel potassium channel opener, on potassium current in rat aortic smooth muscle cells.

1. We evaluated the mechanism of activation by AL0671, a novel potassium channel opener, of potassium current in rat aortic smooth muscle cells. 2. Under conditions of whole cell recording, AL0671 (1-1000 microM) markedly increased potassium current with a Hill coefficient of 2 and dissociation constant of 1.5 x 10(-4) M. This activation was completely inhibited by intracellular ATP. 3. Under inside-out patch conditions, the ATP-sensitive K+ channels (KATP) treated with AL0671 (100 microM) showed prolongation of the slower open time component and shortening of the slower closed time component without modification of channel conductance.

Animals↗
PubMed1995

Change in intracellular K+ concentration caused by external osmolality change regulates sperm motility of marine and freshwater teleosts.

We previously demonstrated that osmolality isotonic to the seminal plasma suppresses sperm motility in marine and freshwater teleosts, and exposure of sperm to hypertonicity of sea water or hypotonicity of fresh water, respectively, induces the initiation of sperm motility at spawning. The motile sperm became immotile by return of osmolality to the isotonic osmolality both in a marine teleost, the puffer fish, and a freshwater teleost, the zebrafish. The initiation and termination of sperm motility could be repeated several times by changing surrounding osmolality in both species. In demembranated sperm, motility was suppressed by a K+ concentration equivalent to the seminal salt concentration in both puffer and zebrafish. Demembranated puffer sperm were reactivated when K+ concentration of the reactivating solution increased. Conversely, initiation of motility in the demembranated zebrafish sperm was induced by decreasing K+ concentration. The initiation and termination of the demembranated sperm were alternately repeated by changing K+ concentration of the reactivation solution in both species. Furthermore, intracellular K+ concentration rose when sperm motility of the puffer was initiated in hypertonic solutions. These results suggest that change in external osmolality is converted into change in intracellular K+ concentration, and that the change affects the flagellar axoneme as a signal to initiate or terminate sperm motility. The initiation and termination of motility in the demembranated puffer sperm were caused at a high pH and a low pH of the reactivating solution, respectively, suggesting the contribution of intracellular pH in the regulation of flagellar motility.

Animals↗
PubMed1995

The two-color analysis of the T-lymphocyte subsets in experimental allergic neuritis in rats.

We examined the T-cell subsets in the peripheral blood, spleen and lymph nodes during the course of experimental allergic neuritis (EAN) by using two-color analysis. In the acute phase, the percentages of CD4+ major histocompatibility complex (MHC)-II+ cells and CD8+ MHC-II+ cells in the lymph nodes of EAN rats were significantly higher than in the control rats. In the recovery phase, the percentage of CD4+ CD45RC+ cells and CD8+ CD45RC+ cells in the lymph nodes in EAN rats were significantly higher than in the control rats. However, significant changes of the T-cell subsets were not detected in either the spleen or the peripheral blood during the course of EAN. These results suggest that CD4+ MHC-II+ cells, CD8+ MHC-II+ cells, CD4+ CD45RC+ cells and CD8+ CD45RC+ cells may play a role in the course of EAN. The relationship between these double staining cells and EAN is discussed.

Analysis of Variance↗
PubMed1995

A new class III antiarrhythmic drug, MS-551, blocks the inward rectifier potassium channel in isolated guinea pig ventricular myocytes.

We have studied the effects of MS-551 on the inward rectifier potassium channel (IK1) in isolated guinea-pig ventricular myocytes by use of whole-cell and single-channel recording techniques. MS-551 (5 microM) blocked the IK1 current. The percent blockade of the peak and steady-state IK1 current by MS-551 was constant at each test potential. In contrast 50 microM MS-551 failed to block either the sodium or the calcium current. Under cell-attached patch conditions, MS-551 reduced the open probability of IK1 channel activity by prolonging the interburst interval without changing either the unitary amplitude or the equilibrium potential. The blockade of IK1 was concentration-dependent. MS-551 did not change either the mean open time or mean closed time within a burst. Extracellular acidification (pH 6.4) strongly attenuated the effect of MS-551 on the open probability of IK1 channel activity when compared with its effect at pH 7.4. In summary, our results demonstrated that MS-551 blocked the IK1 channel. The neutral form of this drug molecules may penetrate the cardiac cell membrane via a hydrophobic pathway to block the steady-state IK1 current by reduction of open probability.

Animals↗
PubMed1995

[High resolution MR imaging of the inner ear apparatus using 3D-Fast spin echo sequence].

To evaluate the efficacy of high resolution MR imaging of the inner ear with 3D-Fast spin echo sequence, one volunteer and 12 patients were imaged with a 1.5 T MR scanner. High resolution T2-weighted images were obtained with a head coil in 13 minutes, and the voxel size was 0.39mm x 0.45mm x 1.2mm in most subjects. Original images and maximum intensity projection (MIP) images of the inner ear were evaluated. On original images, the endolymphatic duct was visualized in 72% of subjects, the cochlear aqueduct in 96%, three branches of the cranial nerves in the internal auditory canal in 100%, and flow void of the vessel in the cerebellopontine angle in 100%. On MIP images, more than two cochlear turns were visualized in 92% of subjects, three semicircular canals in 100%, and the anterior and posterior ampulla in 100%. MR imaging of the inner ear with 3D-Fast Spin Echo sequence provides a variety of useful information regarding the anatomy around the inner ear.

Ear, Inner↗
PubMed1994

[Blood flow in skeletal muscle during and after contraction: intravital microscopies studies].

Using an intravital video microscopy system, the red cell velocities, and the diameters of the capillaries and terminal arterioles were measured in rabbit tenuissimus muscle during and after contraction. Muscle contractions were produced by direct electric stimulation using square waves at 9 V of 0.1 msec duration and 2-6 Hz frequency. The red cell velocity gradually increased after stimulation. It was maximal after contraction in the capillaries, and was maximal during contraction in the terminal arterioles. When the stimulus frequency was high, then the maximal red cell velocity increased and returned to the level at rest more slowly than with low frequency, in both the capillaries and terminal arterioles. The proportion of capillaries with zero or very low velocities was reduced during and after contraction. There were few detectable changes in any capillary diameter during or after contraction. However the terminal arteriole diameter reduced during contraction and was dilated after contraction. These results suggest that the terminal arteriole might play an important part in the skeletal muscle blood flow control during and after contraction.

Animals↗
PubMed1993

Effect of active recovery on intracellular pH following muscle contraction, a 31P-MRS study.

The effect of active recovery after intense muscular exercise was examined by 31P-MRS. Seven healthy males participated in this study, and their right wrist flexor muscles were examined. Each subject flexed the right wrist at 60% of the maximum voluntary contraction (MVC) until the intracellular pH in the wrist flexor muscle decreased to approximately 6.4. This was followed either by active recovery (AR) which consisted of 5, 10, 20, 30 or 40% MVC exercise, and by passive recovery (PR) during a 10-min-recovery period. The intracellular pH (pHi) recovered faster during AR at each condition than during PR. Besides, from the 2nd to the 5th min of the recovery period, the pHi was significantly higher during AR than during PR. The quadratic regression curve of pHi recovery during the 10-min-recovery-period against the % MVC was obtained. The optimal contraction intensity determined from this curve was 8.7% MVC for a 10-min-recovery-period. The optimal levels were determined for another recovery duration within 10 min, and the level decreased with the prolonged recovery duration. These data suggest that mild exercise is an effective maneuver to promote the recovery from intracellular metabolic acidosis, and that the intensity of the recovery exercise should be determined according to the cooling down duration or the resting interval before the subsequent exercise performance.

Adult↗