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T Kitazawa

Publications and source records attributed to T Kitazawa.

135 records · Page 8Linked to original sources
PubMed1976

Physiological significance of Ca uptake by mitochondria in the heart in comparison with that by cardiac sarcoplasmic reticulum.

It was investigated whether mitochondria play a significant role in the physiological regulation of the contractile process by Ca2+ in cardiac muscle in comparison with the sarcoplasmic reticulum (SR). Ca uptake activities of chicken cardiac SR and rabbit cardiac mitochondria were measured by means of centrifugation, dual-wave-length spectrophotometric and Millipore filtration methods. The maximum Ca uptake capacity of cardiac SR was usually 50-60 nmoles/mg protein and the apparent binding constant was 2.0 X 10(6) M-1. The apparent Ca-binding constant of cardiac mitochondria under limited loading conditions was 2.4 X 10(5) M-1 at pH 7.4 and 5.9 X 10(4) M-1 at pH 6.8. In the presence of 100 muM Ca2+ at 28-29 degrees, the estimated initial rate of Ca uptake of cardiac SR ranged from 20 to 30 nmoles Ca/mg-sec, while that of mitochondria was 4.6 nmoles Ca/mg-sec under limited loading conditions at pH 7.4 and 0.64 nmoles Ca/mg-sec under massive loading conditions at pH 6.8, which was much closer to physiological conditions. In the presence of low Ca2+ concentrations, the initial rate of Ca uptake of cardiac SR was 0.5 nmoles Ca/mg-sec at 3.5 X 10(-7) M Ca2+ and that of mitochondria under massive loading conditions at 1 X 10(-6) M Ca2+ was 0.02 nmoles Ca/mg-sec at pH 7.4 and 0.004 nmoles Ca/mg-sec at pH 6.8. The Ca uptake activities were also examined using glycerol-extracted cardiac muscle fibers. Cardiac SR, 1.7 mg/ml, reduced the tension of maximally contracted cardiac muscle fibers to a level corresponding to about 30% of maximum tension, but in the presence of 14.3 mg/ml of mitochondria the maximum tensions of both skeletal muscle and cardiac muscle fibers were maintained for at least 3 min. From these results the time course of relaxation of cardiac muscle induced by cardiac SR or mitochondria was calculated. It was concluded that, in the physiological contraction of cardiac muscle, the SR plays a major role in controlling intracellular Ca2+ movement; the Ca uptake of mitochondria is relatively insignificant. When the cardiac muscle contracts maximally, SR alone cannot relax the cardiac muscle without the aid of other Ca removing system.

Adenosine Triphosphate↗
PubMedDate not supplied

Laser confocal scanning microscopy of the surface membrane/T-tubular system and the sarcoplasmic reticulum in insect striated muscle stained with DilC18(3).

The structure of the surface membrane/transverse tubular (T-tubular) system and of the sarcoplasmic reticulum (SR) of the labial adductor muscle of the honey bee (Apis mellifera) was examined by laser confocal scanning microscopy, after staining with the fluorescent membrane probe DiIC18(3). The following components of the surface membrane/T-tubular system were visualized: transverse tubular networks that are located in the A-band close to the A-I junction and form dyads with the SR, longitudinal tubules that link the T-tubular networks within the between sarcomeres, and surface invaginations of larger diameter that contain tracheoles. The well developed SR forms a dense network of branching and anastomosing tubules in the A-band. A few tubular elements in the interfibrillar space in the I-band link the SR of adjacent sarcomeres. This study demonstrates the advantages of the laser confocal microscope and lipophilic fluorescent dyes for studying the 3-D structure of cellular membrane systems.

Animals↗
PubMedDate not supplied

Calcium ion in cardiac contractility.

Under physiological conditions where the intracellular Ca ion concentration does not exceed 3 X 10(-6) M, the sarcoplasmic reticulum plays a major role in the relaxation process of cardiac muscle; mitochondria do not take up a significant amount of Ca ion during this process. If cardiac muscle undergoes maximum contraction, in which the intracellular Ca ion concentration should reach 10(-4) M, the role of mitochondria in reducing intracellular Ca ion becomes appreciable. The relationship of the tension developed by cardiac glycerinated muscle fibers to the Ca ion concentration resembles the relationship of the amount of bound Ca of cardiac troponin to the Ca ion concentrations, being less steep in its slope compared with those of fast and slow skeletal muscles. This gentle slope seems to reflect the great diversity of affinities for Ca ion of the two Ca-binding sites of cardiac troponin, one being about 100 times that of the other.

Animals↗
PubMedDate not supplied

Bilateral hypoplastic internal carotid arteries with multiple cerebral aneurysms.

A 60-year-old man with massive subarachnoid hemorrhage is reported. Radiologically, bilateral occlusion of the internal carotid arteries and multiple cerebral aneurysms of the saccular type were detected. Postmortem examination revealed that the internal carotid arteries were markedly diminutive and completely occluded by mesenchymal fibrous tissue. The pathogenesis of the diminutive internal carotid arteries and the cerebral aneurysms were briefly discussed.

Carotid Artery Thrombosis↗