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B P Yu

Publications and source records attributed to B P Yu.

144 records · Page 8Linked to original sources
PubMed1974

The role of platelet membrane phospholipids in the platelet release reaction.

The structure and function of the platelet surface was probed by phospholipase C (Clostridium perfringens) which hydrolyzes membrane phospholipids, particularly phosphatidylcholine. Platelet phospholipids were susceptible to phospholipase C, and extent of hydrolysis was dependent on concentration of phospholipase C and Ca(++). Phospholipase C (0.15 U/ml) with Ca(++) (0.55 mM) hydrolyzed 15.6% phospholipids during 5 min. Phospholipase C released platelet serotonin (5HT), ADP, and platelet factor 4. Hydrolysis of 5% phospholipids resulted in release of 70% 5HT. Platelet 5HT release was rapid, occurring within 2 min. Phospholipase C (0.2 U/ml) with Ca(++) (0.55 mM) also released 10.35 nmol sotrage pool ADP/10(9) platelets and 63% platelet factor 4 during 3 min. Phospholipase C did not cause leakage of cytoplasmic metabolic pool ADP, since only 6.6% [(3)H]ADP was released. Ultrastructural analysis of phospholipase C-modified platelets showed that platelets were intact. After 2% phospholipid hydrolysis, centralization of granules and contraction of microtubules were evident. After 18% phospholipid hydrolysis, there were morphological indications of degranulation. Phospholipase C-induced phospholipid hydrolysis caused the release of ADP and 5HT since: (a) Phospholipase C purified by heating was shown to be free of protease and neuraminidase activity and capable of inducing the platelet release reaction. (b) Antitoxin (Cl. perfringens) neutralized phospholipase C-induced 5HT release which rules out a contaminant. (c) Phosphorylcholine, the hydrolysis product, did not induce platelet 5HT release. This study demonstrates that minimal hydrolysis of platelet phospholipids triggers the release reaction. Our hypothesis is that phospholipids, presumably phosphatidylcholine, are situated at or near active site or "receptor" on the platelet surface and function as the modulator for the release reaction.

Adenosine Diphosphate↗
PubMed1974

Role of sarcoplasmic reticulum phospholipids in calcium ion binding activity.

The relationship between sarcoplasmic reticulum phospholipid and Ca(2+) binding by sarcoplasmic reticulum membranes was explored. Ca(2+) bound in the absence of ATP was defined as "ATP-independent Ca(2+) binding," and the additional amount of Ca(2+) bound in the presence of ATP was defined as "ATP-dependent Ca(2+) binding." The latter was found to be very sensitive to the loss of sarcoplasmic reticulum phospholipid; the amount of Ca(2+) bound was reduced when as little as 3% of the phospholipid was destroyed by phospholipase C. Further destruction of membrane phospholipid up to a 40% loss caused little or no further reduction of this Ca(2+) binding. However, when the destruction of phospholipid exceeded 40%, further loss of this Ca(2+) binding occurred, and there was an almost complete loss of this function when more than 60% of the sarcoplasmic reticulum phospholipid was destroyed.

Adenosine Triphosphate↗
PubMed1972

Analysis of a calcium ion binding system composed of two different sites.

Using murexide (Mx), a metallochromic indicator, and a dual wavelength spectrophotometer with a high signal-to-noise ratio, the Ca(++) binding in a system containing two classes of binding sites was studied. Solutions with solute containing one or two classes of Ca(++) binding sites and without such solute were titrated with Ca(++) using Mx as an indicator of free Ca(++) concentration. Since curvilinear Scatchard plots are obtained from titration curves of solutes containing two classes of binding sites, a computer program was developed to resolve such plots into two linear partial plots, each corresponding to a single class of binding site. The validity of the procedure was examined with solutions of ethylene glycol bis(beta-aminoethyl)-N-N'-tetraacetic acid, adenosine triphosphate (EGTA, ATP), or a mixture thereof. The method was also applied to biological material and it was found that a protein fraction isolated from rat skeletal muscle sarcotubular membranes, termed Fraction-2 (Fr-2), has two classes of binding sites for Ca(++); the association constants of the high affinity site and low affinity site are 4.3 x 10(5) M(-1) and 9 x 10(3) M(-1), respectively. The advantages and limitations of this methodology are discussed.

Acetates↗
PubMed1968

Relation of lipid structure of sarcotubular vesicles to Ca++ transport activity.

The role of lipids of the sarcotubular membranes in their Ca(++) uptake and Mg-ATPase activities was investigated. Treatment of the membranes with phospholipase C inhibits both processes. Treatment with phospholipase A and phospholipase D, which results in massive hydrolysis of the sarcotubular phospholipids, does not inhibit either the Ca(++) uptake or the Mg-ATPase activities, nor does treatment with the polyene antibiotics affect these processes. Essential fatty acid deficiency alters sarcotubular membrane lipids; they contain much less stearic, linoleic, and arachidonic acids and much more oleic and eicosatrienoic acids than normally, but do not lose the ability to actively sequester Ca(++). It is concluded that neither nonpolar lipids nor the nonpolar regions of polar lipids are involved in Ca(++) sequestering and Mg-ATPase activities of the sarcotubular membranes. Of the polar components, the phosphoryl moiety of the phospholipids is required for both activities. However, the phosphoryl group appears to be required for the maintenance of the membranous structure necessary for Ca(++) sequestration rather than serving specifically in the active transport process. That treatment with phospholipase D, which results in the conversion of much of the sarcotubular phospholipid from a dipolar to an anionic structure, does not affect Ca(++) uptake activity is a most remarkable finding.

Adenosine Triphosphatases↗
PubMedDate not supplied

Physical activity as a factor in the action of dietary restriction on aging: effects in Fischer 344 rats.

Dietary restriction (DR) slows the rate of aging in laboratory rodents but the mechanism of action is unknown. DR is known to induce beneficial effects in a variety of tissues and organ systems. DR also maintains high levels of physical activity over the life span. We tested the hypothesis that lifelong physical activity is an important component of the anti-aging action of DR. Male specific pathogen-free Fischer 344 rats were divided into 4 groups at 6 weeks of age: A: fed old libitum; AE: fed ad libitum and in cages with running wheels; B: fed 60% ad libitum; BE: fed 60% ad libitum and in cages with running wheels. Running activity and spontaneous cage activity were measured over 24 hours and over the life span. Metabolic rate was measured indirectly by analysis of air entering and leaving cages. AE rats exhibited low levels of running activity and ran very little beyond 6 months of age. In contrast, BE rats sustained high running levels even after all A and AE rats had died. High levels of wheel running did not decrease spontaneous cage activity. Median life span (50% survival) was in the order A = AE < B < BE. Ten percent survival was in the order A = AE < B = BE. BE rats had greatest median life span and also highest specific metabolic rate. Exercise and DR altered pathology: At death BE rats had a high incidence of cardiomyopathy, whereas A and AE rats had high incidence of chronic nephropathy and pituitary tumors. The data indicate that increased physical activity is probably not an important factor in the action of DR on aging.

Aging↗
PubMedDate not supplied

The effect of rat age on the composition and functional activities of skeletal muscle sarcoplasmic reticulum membrane preparations.

The complex of membranes of which cells are comprised have been considered as likely sites of deterioration underlying the decline on physiologic competence with age. Although this concept is an attractive one on theoreical grounds, few direct experimental data are available on the effect of age on biological membranes. Since the sarcoplasmic reticulum of skeletal muscle has been well characterized and is an easily studied membrane system in regard both to its composition and function, the effect of age on this membrane system was explored. Rats of 1, 2, 3, 6, 12, 24 and 28 months of age were the source of sarcoplasmic reticulum membranes which were characterized by the following measurements: phospholipid/protein weight ratio; phospholipid composition; the activity of the (Ca++ + Mg++) -ATPase and the steady state concentration of its phosphorylated intermediate; the ATP-dependent, oxalatepromoted Ca++ transport activity. Although there were some differences between age groups in these basic parameters of sarcoplasmic reticulum composition and function, the data obtained provide no clear evidence of deterioration of these membranes with age.

Adenosine Triphosphatases↗
PubMedDate not supplied

Morphometric analysis of somatotrophs: effects of age and dietary restriction.

We investigated changes in the cell number of somatotrophs in the anterior pituitary of male F344 rats caused by age and lifelong dietary restriction (DR). Morphometric and immunohistochemical techniques were performed on the pituitary gland at 6, 18, and 24 months of age. In ad lib fed (AL) rats, cell density of somatotrophs progressively decreased with age. However, when normalized according to the increased volume of the anterior lobe, which occurs during aging, the total number of somatotrophs remained constant until 18 months, then decreased. In contrast, the cell density of DR rats was not affected to the same extent as that of AL rats, and the total number of cells seemed to remain constant through 24 months, thus, retarding the age-related numerical changes. However, the cell number in DR rats, when normalized by body weight, was larger than that found in AL rats. We also found that average cell volume of somatotrophs shows little age or dietary restriction effects, but the nucleus volume significantly increases at 24 months in both groups. The numerical changes which occur in somatotrophs during the aging process may be associated with the aging phenomena found in GH secretion.

Aging↗
PubMedDate not supplied

Change in endocrine pancreatic function in short-term diet restriction.

Long-term diet restriction can retard the aging process. Lower sustained plasma glucose levels may be one of the key factors for prolongation of life. The purpose of this study was to determine the effects of short-term diet restriction on the endocrine pancreas in rats. One hundred 5-wk-old male Sprague-Dawley rats were fed ad libitum for 1 wk, and then 10 rats (5 fed, 5 fasted for 24 h) were killed. The remaining 90 rats were divided into two groups, either fed ad libitum or maintained on a restricted food intake (60% of control/day). At regular intervals after the start of food restriction, rats from each group were killed, and plasma and the pancreas were collected for measurements of glucose, insulin, and glucagon concentration and content. At the end of the study, isolated pancreatic perfusions were performed to examine dynamic insulin response to glucose. Throughout the study, plasma glucose and insulin levels were lower in fed rats from the diet-restricted group than in fed rats from the normally fed group. Furthermore, there were no differences in plasma glucose or insulin levels between fed and fasted rats in the diet-restricted group. Pancreatic perfusion showed that the second phase of insulin release was significantly lower in rats from the diet-restricted group than in rats from the normally fed group. Decreased content of spermine in the pancreas of the diet-restricted rats may correlate with a decreased second phase of insulin release. These findings may partly explain why lowered plasma insulin levels are observed in diet-restricted rats.

Aging↗