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Biomedical subjects

T Osaka

Publications and source records attributed to T Osaka.

At least 73 records · Page 4Linked to original sources
PubMed1991

Developmental changes in calcium currents of rabbit ventricular cells.

We investigated the postnatal development of L-type Ca2+ current (ICa) in enzymatically isolated adult (AD) and newborn (NB) (1-3-day-old) rabbit ventricular cells using the whole-cell, patch-clamp method. ICa was recorded with Cs(+)-rich pipettes and a Na(+)- and K(+)-free bath solution at 36 degrees C to eliminate other currents. ICa density (obtained by normalizing ICa to the cell capacitance) was significantly higher in AD cells than in NB cells at potential levels between 0 and +50 mV with 1.8 mM Ca2+ as the charge carrier. There was no shift in the current-voltage relation between AD and NB cells. The maximum ICa density was 9.9 +/- 2.0 pA/pF at 14 +/- 5 mV in AD cells (n = 11) compared with 5.6 +/- 2.0 pA/pF at 13 +/- 5 mV in NB cells (n = 7) (mean +/- SD). Time to half inactivation (T 1/2) showed a nearly U-shaped relation to membrane potentials from -10 to +30 mV with the shortest T 1/2 at the potential giving the maximum ICa density in both groups. T 1/2 at 0 and +10 mV was slightly but significantly longer in NB cells (16.8 +/- 4.6 and 13.5 +/- 2.4 msec, respectively) than in AD cells (12.6 +/- 3.0 and 10.6 +/0 1.5 msec).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium Channels↗
PubMed1991

Experimental model of effects on normal tissue of injury current from ischemic region.

An ischemic myocardial region contains cells with a depolarized resting membrane potential. This depolarization leads to an intercellular current flow between the ischemic region and the surrounding normal myocardial cells, which has been termed an "injury current." We have devised an experimental model system in which an isolated rabbit ventricular cell is electrically coupled to a model depolarized cell to evaluate the effects of this injury current on the electrical properties of a normal ventricular cell. We found that the action potential duration of the isolated cell could be reversibly altered by varying the coupling resistance such that the action potential duration was shortened by high values of coupling resistance but could be considerably prolonged by lower resistance coupling. We did not observe automaticity in the isolated cell as a consequence of coupling to the depolarized model. The changes in action potential duration were accompanied by alterations in the frequency at which the isolated cell could respond to repetitive stimuli. In addition, the depolarization of the isolated cell produced by the electrical coupling led to a significant increase in the cellular excitability. This last effect may be of particular importance in understanding the mechanisms for origination of arrhythmias in the border zone of myocardial ischemia.

Action Potentials↗
PubMed1991

[% fat of Nepali children (ranging from 6 to 18 years old) having different living style].

A comparative study of % fat was carried out on Nepali children (Ranging from 6 to 18 years old) to clarify the cause of obesity attended with modernization. 126 males and 79 females who have a natural living style, in rural district (KV) and 166 males and 133 who have a living style affected by the rapid urbanization, in suburban district (BV) were selected as subjects. %Fat was estimated from skinfold thickness according to the method of Nagamine (1975). The results summarized as follows. 1) Mean %Fat of BV in each age were clearly higher than those of KV with coincidental age, especially in male subjects. 2) According to the previous reports (Yoshimizu et al., 1990; Ito et al., 1989), it's considered physical activities in the subjects of BV were lower than those of the subjects in KV. But we could not found the nutritional factors to explain the difference of % fat between BV and KV. From these results, it's considered the difference of % fat in both districts is due to the difference of their physical activities.

Adipose Tissue↗
PubMed1991

[Solitary ostial coronary artery stenosis in women].

Among 6,200 patients undergoing coronary arteriography using the Sones technique at the Juntendo University Hospital and the Juntendo Urayasu Hospital from 1975 to 1988, 121 patients (1.95%, 111 males and 10 females) were found to have significant (> or = 50%) stenosis in their left main trunks (LMT). Patients with systemic inflammatory disease such as syphilis or Takayasu's arteriitis, aortic valvular disease, or a history of mediastinal irradiation were excluded from this study. Stenotic lesions of the LMT were categorized into 7 types according to their locations and appearances. 1. The most common type was stenosis localized just before the branching from the left circumflex artery (42 patients or 34.7%). 2. Although the incidence of left coronary ostial stenosis was not very high (13 patients, 10.7%) as a whole, that for the female patients was the highest (30.8%) of the 7 types. Nine patients showed atherosclerotic irregularities with or without significant stenosis in the distal coronary arterial trees. Four patients, including 3 women, were diagnosed as "primary solitary ostial stenosis" of which the cause is unknown. All of the 3 women were premenopausal, and their clinical profiles were as follows: Case 1 (45-year-old): She was hospitalized because of anterior chest pain during exertion or at rest. Her electrocardiogram (ECG) showed severe ischemic ST-T changes. Coronary cineangiography disclosed a 95% stenosis in the left coronary ostium, and the distal portion of the coronary artery was normal. She had not experienced angina after her coronary artery bypass operation. Case 2 (45-year-old): She was hospitalized because of exertional chest pain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

[An operative case of solitary interruption of the aortic arch in adult].

A 43-year-old lady was hospitalized due to easy fatiguability in the legs during exercise, and for evaluation of an abnormal shadow in the chest X-ray, and hypertension. Her blood pressure was 200/80 mmHg in the right arm, 140/70 mmHg in the left, and 110/70 mmHg in both lower extremities. Systolic vascular bruit radiating to her neck and back was audible in the Erb's area. DSA and aortogram disclosed extremely dilated vessels around the origin of the left common carotid artery. The left subclavian artery was opacified retrogradely as a subclavian blood steal via the left vertebral artery, and mild stenosis was seen at its origin. There was no evidence of associated congenital anomaly such as VSD, PDA, or ASD. The final diagnosis, solitary interruption of the aortic arch (S-IAA, type B), was made by MRI. The patient had an extra-anatomical bypass operation by using Cooley woven dacron graft from the ascending to the abdominal aorta. The result was good. S-IAA is a very rare congenital anomaly. As far as we know, only 21 patients with S-IAA including this case have been reported. A physician should be aware that a patient with S-IAA tends to have a difference of blood pressure not only between the upper and lower extremities but also between both arms, and pressure in the right arm is usually higher than that in the left. These are good signs to suspect S-IAA. And they also can be helpful to differentiate S-IAA from coarctation of the aorta.

Angiography, Digital Subtraction↗
PubMed1990

Osmotic responses of rat paraventricular neurons by pressure ejection method.

Extracellular recordings were made from 44 spontaneously active neurosecretory and 43 unidentified neurons in the paraventricular nucleus (PVN) of the hypothalamus in urethane-anesthetized rats. Physiologically hypertonic (+30 mOsm/kg, NaCl or mannitol) and hypotonic (-30 mOsm/kg) solutions were applied by pressure through multibarrel micropipettes to the immediate vicinity of neurons. Of 44 neurosecretory neurons tested, 31 (70%) were unaffected by locally applied osmotic stimulation, and the remaining 13 were excited. Of these 31 osmotically unresponsive neurosecretory neurons, 21 were further tested with very strong hypertonic (+260 mOsm/kg, NaCl) solution, and only 7 were affected. Of 43 unidentified neurons, 28 (65%) were unaffected by osmotic stimulation, and 12 were excited. Accordingly, only parts (30%) of both the neurosecretory and unidentified neurons in the PVN were found to be osmosensitive. We concluded that some neurons in the rat PVN are osmosensitive and osmosensitivity is not specific to neurosecretory neurons in the PVN.

Action Potentials↗
PubMed1990

Cellular mechanism of the functional refractory period in ventricular muscle.

A premature action potential elicited in ventricular muscle during the functional refractory period of a preceding action potential requires an increased stimulus intensity for successful propagation. We measured the cellular basis for these relative decreases in tissue excitability during the recovery phase by performing parallel experiments on rabbit left papillary muscle and isolated rabbit ventricular cells in addition to conducting theoretical studies with numerical simulations of action potential initiation. For each experimental preparation, the pacing protocol consisted of a train of 10 stimuli (S1) at an S1-S1 interval of 500 msec with a premature stimulus (S2) of variable S1-S2 intervals following the tenth S1 action potential. The stimulus threshold for initiation of an S2 action potential (I2) was then measured as a function of the time of occurrence of the S2 stimulus relative to the time of 95% repolarization of the tenth S1 action potential (stimulus delay [SD] time). In the tissue preparation, the I2 increased sharply for SD times less than 0 msec to a value that was 100% above the S1 stimulus threshold for SD time = -5 +/- 2.4 msec (n = 8). Similar experiments on the isolated ventricular cell showed no increases in I2 as a function of SD time but rather significant decreases in both the action potential amplitude (APA) and the maximum rate of rise of the action potential upstroke (Vmax) of the S2 action potential. The APA and Vmax for the S2 action potential were decreased to 50% of the S1 action potential values for SD time = -5.2 +/- 2.1 msec and SD time = 0.3 +/- 1.6 msec, respectively (n = 8). Both parameters reached 100% recovery by SD time = 10 msec. These results and our numerical simulations are consistent with the hypothesis that the decreases in tissue excitability that occur with premature stimulation have a cellular mechanism as a result of a decrease in cellular responsiveness (APA, Vmax) rather than an intrinsic decrease in cellular excitability.

Action Potentials↗
PubMed1990

[A comparative study of % fat and living style on nepalese].

Measurements of %Fat, nutrient intake and maximal aerobic power (MAP) were carried out on Nepalese to clarify the cause of obesity attended with modernization. One hundred thirty-two males (KV) who have a natural living style, 20-84 years of age, in rural district and 237 males who have a living style affected by the rapid urbanization, in surburban district were selected as subjects. The subjects of surburban district were divided into two groups. One of them included 147 farmers (BF) who engage in not mechanized farming, 20-73 years of age. Another group included 90 students and wage laborers (BNF) who go to and from Kathmandu (the capital of Nepal), 20-57 years of age. %Fat was estimated from skinfold thickness according to the method of Nagamine (1975). The survey for the nutrient intake was carried out by the 24-hour recall method to obtain the individual food consumption using the food models. Measurement of MAP was made indirectly by the modified of Margaria et al (1965). The main results are summarized as follows. 1) Mean %Fat and the appearance rates of obesity in each age group showed high values in following order: BNF greater than BF greater than KV. 2) Mean caloric intake in KV was higher than those in BF and in BNF an almost all age groups and no significant difference was found between BF and BNF in all age groups. 3) No significant differences in mean fat intake and in mean animal fat intake among all groups were found in almost all age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Variations with age and serum cholesterol level in the topographic distribution of macroscopic aortic atherosclerotic lesions as assessed by image analysis methods.

The topographic distribution of macroscopic atherosclerotic lesions in the aorta was studied by image analysis of aortas taken at autopsy from 155 males aged 10 to 54 yr. In both the thoracic and abdominal aorta, fatty streaks (FS) appear before raised lesions (RL) affecting preferential areas located longitudinally along the intercostal ostia, at the aorta bifurcation, and surrounding the points of origin of branches of the abdominal aorta. Later RL appear in the same areas of the aortic intima affected by FS at younger ages. As for the effect of serum total cholesterol (TC) in the progression of atherosclerosis, the prevalent involvement areas by FS and RL were similarly distributed as indicated by our analyses. However, areas showing frequent occurrence of FS and RL in each aortic segment were distributed more extensively at identical areas in the higher serum TC groups than in the lower TC level group. Thus, it can be concluded that FS are the precursor lesions of RL in the aorta and that the serum TC promotes the progression of atherosclerosis.

Adolescent↗
PubMed1990

[A case of acute myocardial infarction due to coronary embolism from left atrial thrombus with atrial fibrillation].

A 55-year-old man, who has been on follow-up observation with chronic atrial fibrillation, came in with a sudden onset of chest pain on July 31, 1986. He was diagnosed as having acute myocardial infarction indicated by abnormal ECG, elevated serum enzyme and characteristic signs of echocardiography. Emergency coronary angiography was performed 2 hours after the onset of chest pain, and it was reported as showing total obstruction of the distal left anterior descending artery. Percutaneous transluminal coronary recanalization using 1,200,000 units of urokinase was unsuccessful. The repeated angiography performed 40 days later, showed normal coronary arteriogram, but left ventriculogram revealed akinesis of the apical segment. Furthermore, left atrium opacified in the levophase of pulmonary arteriogram indicated left atrial thrombus. The cause of the myocardial infarction was considered to be coronary embolism from the left atrial thrombus with atrial fibrillation. It must be the first report documented by coronary angiography, of coronary thrombo-embolism due to chronic atrial fibrillation without any underlying disease.

Angioplasty, Balloon, Coronary↗
PubMed1989

Activity of hypothalamic neurons in conscious rats decreased by hyperbaric environment.

Single-unit activity of neurons in rat hypothalamus, prefrontal cortex (PFC) and central medial thalamus (CM) was recorded through chronically implanted electrodes. Upon being subjected to 7 atmospheres absolute (ATA) hyperbaric air (709 kPa) environment, about two-thirds of the hypothalamic neurons tested reversibly decreased their firing rate to 71 +/- 12% (mean +/- SD, n = 25) compared to the precompression control activity, and the remaining one-third did not change their firing rate (100 +/- 6%, n = 13). It is suggested that the decrease in firing rate was attributable to increased partial pressure of both oxygen and nitrogen. In contrast to the hypothalamus, the firing rates of most neurons in the PFC and CM did not decrease (99 +/- 9% for PFC, 107 +/- 12% for CM). In separate acute experiments, 3 out of 5 hypothalamic neurons tested in the isolated forebrain also decreased their firing rates in hyperbaric environment. The results suggest that the hyperbaric air acted directly on the forebrain and depressed more than half of the hypothalamic neurons.

Action Potentials↗
PubMed1989

Developmental changes in the electrophysiologic properties of rabbit papillary muscles.

We studied the electrophysiological properties of adult (AD) and newborn (NB) rabbit papillary muscles in vitro with superfusion of normal Tyrode's solution, solutions with elevated [K+]o, and in solutions with various concentrations of tetrodotoxin. In control solutions, the NB papillary muscles had a more negative resting membrane potential (-83.6 +/- 1.2 versus -80.0 +/- 1.5 mV), a higher rate of rise of phase 0 (134 +/- 5 versus 120 +/- 5 V/S) and a higher, longer-lasting action potential plateau than the AD papillary muscles. Exposure to elevated [K+]o led to a significant post-repolarization refractoriness in AD papillary muscles that was more than that for NB papillary muscles even when NB papillary muscles were depolarized to the same resting membrane potential as the AD papillary muscles. The NB papillary muscles were comparatively resistant to tetrodotoxin in terms of percent reduction of conduction velocity and percent rise in the current threshold for excitation. The conduction velocity for AD papillary muscles in control solution (66 +/- 6 cm/s) was more than for NB papillary muscles (44 +/- 4 cm/s), which would not be expected from the data on the rate of rise of the action potential, suggesting that the cable properties of NB papillary muscles (specifically a greater surface to volume ratio of the ventricular cells) are also significantly different from the AD papillary muscles.

Action Potentials↗
PubMed1989

Variations with age in the topographic distribution of coronary atherosclerotic lesions as assessed by image analysis.

The localization of macroscopic coronary atherosclerotic lesions was investigated for 184 cases by image analysis. Atherosclerotic lesions were classified into 2 types: fatty streaks and raised lesions. The overall distribution of fatty streaks in arteries involved only by fatty streaks and the distribution of raised lesions in those arteries having raised lesions were demonstrated at similar sites in 3 coronary vessels. If the localization of lesions was examined within age groups, those sites involved with fatty streaks in one age group were replaced with raised lesions in the next older age group; fatty streaks in this older group were located distally to the raised lesions. Subsequently the areas occupied with fatty streaks were replaced with raised lesions in the next older age group. Furthermore, raised lesions seldom appeared at the site where fatty streaks had not existed in the preceding age group. Similar changes in topographic distribution were present if such changes were analyzed according to extent of atherosclerosis. Data from cases with myocardial bridges show that both fatty streaks and raised lesions are seldom observed in the region distal to myocardial bridge. We conclude, thus, that fatty streaks are the precursors of raised lesions in the coronary artery.

Aging↗
PubMed1988

Effects of iontophoretically applied cortisol on tuberoinfundibular neurons in hypothalamic paraventricular nucleus of anesthetized rats.

Effects of cortisol on 22 tuberoinfundibular (TI) neurons in the paraventricular nucleus (PVN) of the hypothalamus were examined in urethane-anesthetized rats. Iontophoretically applied cortisol excited 10 (45%) of 22 TI-neurons tested, whereas the cortisol inhibited 4 (31%) of 13 neurons in the periventricular hypothalamic nucleus. Intravenously applied cortisol (0.5 mg in 0.5 ml saline) excited 4 (36%) of 11 TI neurons tested and inhibited 1 (9%). These results suggest that cortisol may have an excitatory effect on TI neurons in the PVN.

Action Potentials↗
PubMed1988

Effects of bepridil on ventricular depolarization and repolarization of rabbit isolated hearts with particular reference to its possible proarrhythmic properties.

1. Effects of bepridil on ventricular depolarization and repolarization sequences were examined in rabbit Langendorff-perfused hearts. 2. In distant bipolar electrograms (DBEs), bepridil, 10(-6) M, caused a significant prolongation of QT intervals. At 10(-5) M, the QT prolongation was further enhanced, and a significant prolongation of QRS duration was also observed. Polymorphous ventricular tachycardia was frequently induced by a single premature stimulus at the higher concentration. 3. In epicardial electrograms recorded through modified bipolar electrodes, bepridil, 10(-6) M, prolonged the interval from the peak negative deflection of the QRS complex to the apex of the T wave (Q-aT), which corresponded to the intracellular action potential duration at 90% repolarization (APD90). The Q-aT prolongation was larger in the base than in the apex, resulting in a marked distortion and dispersion of repolarization. The epicardial activation sequence was unaffected. 4. At 10(-5) M bepridil, the dispersion of repolarization was much more enhanced by activation delay in the epicardial surface. 5. These findings suggest that bepridil causes regionally different lengthening of APD in ventricular muscle leading to an increase in temporal dispersion of repolarization, and that this dispersion may be inducive for re-entrant arrhythmias when accompanied by slow conduction at toxic doses.

Animals↗
PubMed1988

Inhibition of paraventricular neurons by subfornical organ and AV3V in cats.

The study was designed to examine, by electrophysiological techniques, influences of rostral periventricular structures on neurons in the hypothalamic paraventricular nucleus (PVN) in a large animal (the cat) in which stimulating and recording sites could be precisely identified. Extracellular single action potentials were recorded from the PVN in pentobarbital sodium-anesthetized and hemispherectomized cats. Of 246 neurons tested, 24-47% were inhibited and 9-21% were excited by electrical stimulation of the subfornical organ (SFO), the nucleus preopticus medianus (POMn), and the organum vasculosum of the lamina terminalis (OVLT). The onset latencies of inhibition (19-26 ms) were shorter than those of excitation (28-80 ms). Responses of both neurosecretory and nonneurosecretory neurons were similar to the stimulation of all sites tested. Among these sites, the POMn had the strongest influence on the PVN in view of the proportion of the responsive neurons. Moreover, antidromically evoked action potentials in the PVN neurons (n = 10) were only observed after stimulation of the POMn. Chemical stimulation of POMn and SFO by microinjection of sodium glutamate (50-100 nl, 0.5 M) also inhibited 16 of 38 PVN cells; the remaining neurons were unaffected. These results suggest that activation of the POMn, OVLT, and the SFO neurons mainly inhibits the PVN neurons in the cat.

Action Potentials↗