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Biomedical subjects

S Raha

Publications and source records attributed to S Raha.

51 records · Page 3Linked to original sources
PubMed1992

Adhesion efficiency, platelet density and size.

We have previously shown that adhesion of human platelets to immobilized collagen is extremely rapid, with initial rates approaching 3% of single particles adhering per 10 ms. Here, we have investigated adhesion efficiency to collagen as a function of platelet density. Platelet subpopulations: low-density (1.040 < d < 1.065 g/ml), intermediate-density (1.065 < d < 1.070 g/ml) and high-density (1.070 < d < 1.080 g/ml) were separated by Percoll density gradient centrifugation. They constituted 24%, 47% and 29% of the total platelet population and had mean volumes of 6.01, 7.37 and 8.21 fl, respectively. Using a continuous-flow, micro-affinity column, we found that the most dense (large) platelets exhibited initial rate of adhesion 4 times greater than the least dense (small) platelets. They were also less sensitive to inhibition by prostacyclin (PGI2). In contrast, there was no significant difference in aggregation induced by high doses of ADP and collagen, indicating that the most dense platelets were not preferentially involved in aggregation induced by high doses of agonists. These results suggest that normal circulating platelets can be distinctly heterogeneous in their ability to adhere to collagen under arterial-flow conditions. The greater efficiency of high-density platelets may be related to increased content of the glycoprotein Ia/IIa (GPIa/IIa) complex.

Antigens, CD↗
PubMed1991

Percutaneous endoscopic gastrostomy.

Percutaneous endoscopic gastrostomy is a useful alternative to long-term nasogastric feeding or surgical gastrostomy for dysphagic patients. It is simple to perform and is relatively safe.

Deglutition Disorders↗
PubMed1990

Simultaneous isolation of total cellular RNA and DNA from tissue culture cells using phenol and lithium chloride.

A rapid procedure for the isolation of intact total cellular RNA from cultured cells is described. This method combines the simultaneous disruption of cells and extraction of nucleic acids in a single step with the use of phenol and a buffer containing 100 mM LiCl. Total cellular RNA can be isolated in approximately 2 hours. The yield and quality of the RNA is comparable to the more widely employed methods requiring extensive preparatory steps such as extraction using guanidinium thiocyanate and subsequent CsCl gradient centrifugation. The RNA isolated using our procedure contains transcripts up to 10 kb in length and is suitable for Northern analysis. This procedure also yields high-molecular-weight DNA, which is a suitable substrate for restriction endonucleases.

Adrenal Gland Neoplasms↗
PubMed1989

Correlation of membrane anisotropy with function in subpopulations of human blood platelets.

Human blood platelets were fractionated on a discontinuous Percoll gradient into high density (HD), intermediate (ID), and low density (LD) platelets. The subpopulations were characterized with regard to [14C]serotonin uptake and release, cAMP content, aggregation, and membrane anisotropy, which is inversely related to membrane fluidity. Membrane anisotropy, which was high in LD platelets, was found to decrease with increasing density (LD greater than ID greater than HD). LD platelets showed significant lower cAMP levels and [14C]serotonin uptake than the total platelet population (TPP) and ID and HD platelets. Upon ADP and serotonin stimulation the cAMP content was reduced in all platelet populations with the exception of HD platelets in which cAMP was unchanged. Upon thrombin stimulation the cAMP content was reduced only in TPP and LD platelet population and it was increased in HD platelet population. Thrombin activation changed the anisotropy only in LD platelets. Thrombin at a concentration of 0.001 U/ml reduced whereas 0.01 and 0.05 U thrombin/ml increased the membrane anisotropy significantly. As compared with TPP and the other subpopulations, LD platelets were most sensitive upon ADP and thrombin stimulated [14C]serotonin release as well as upon ADP, serotonin and thrombin induced aggregation. The findings suggest that the differing functional abilities of the platelet subpopulations are correlated to the various membrane anisotropies observed in these fractions.

Adenosine Diphosphate↗
PubMed1988

KRDS--a tetrapeptide derived from lactotransferrin--inhibits binding of monoclonal antibody against glycoprotein IIb-IIIa on ADP-stimulated platelets and megakaryocytes.

Short peptides isolated from fibrinogen and K-casein have been shown to inhibit platelet aggregation and fibrinogen binding to stimulated platelets. We studied the effects of synthetic peptides occurring in milk proteins (bovine K-casein, KNQDK, and human lactotransferrin, KRDS) and in fibrinogen (RGDS and L10) on subsequent binding of monoclonal antibodies (MoAb) against the glycoprotein (GP) IIb-IIIa complex (AP2 and P2) on adenosine diphosphate (ADP)-stimulated and unstimulated human platelets and megakaryocytes (MKs) by using an immunoperoxidase method to visualize antibody binding. Only KRDS (900 mumol/L) inhibited the binding of AP2 and P2 on ADP (5 mumol/L)-stimulated platelets, but not on unstimulated platelets. However, the binding of P2 was considerably more inhibited than that of AP2 as judged by immunoperoxidase intensity. Radiolabeled AP2 binding was inhibited by 30% with KRDS on ADP-stimulated platelets as compared with platelets incubated in the absence of ADP. KRDS did not inhibit the binding of MoAbs against GP IIIa (SZ 21), GP IIb (SZ 22), and GP Ib (SZ 2) on ADP-stimulated human platelets. Inhibition of P2 binding by KRDS was also observed in a section of MKs isolated from human bone marrow and stimulated by 15 or 20 micron ADP. A lower concentration of ADP (5 or 10 mumol/L) failed to produce any inhibition of binding. This indicates that MKs may not be equally responsive to agonists as platelets. Moreover, P2 binding inhibition was observed in a larger (P less than .001) percentage of mature MKs (29%) as compared with younger, maturing MKs (11%). The observations suggested that a functional ability possessed by platelets, namely, agonist-induced exposure of the site of interaction of KRDS, may occur at a late stage of MK development.

Adenosine Diphosphate↗
PubMed1985

Isolation of mouse megakaryocytes. I. Separation of two fractions enriched in different maturational stages.

Megakaryocytes (MK) were isolated from mouse bone marrow by centrifugation on discontinuous gradients of isotonic albumin or Percoll and characterized by acetylcholinesterase (AChE) staining. The apparent density distributions of MK varied greatly depending upon the nature of the gradient medium and the composition of the cell suspension buffer while the density range of the other bone marrow cells remained largely unchanged. The present findings also indicate that the unusual morphological and functional characteristics of MK may underlie the observed shift in their density profile. Thrombocytopoietic stimulatory factor (TSF) was administered to mice 18 h before killing to elevate the normally low numbers of earlier MK in the bone marrow and to improve the yield of immature MK during the subsequent isolation procedure. Cells belonging to earlier stages in maturation were separated from the more mature ones on discontinuous Percoll density gradients, providing a basis for further investigation of MK development.

Acetylcholinesterase↗
PubMed1985

Isolation of mouse megakaryocytes. II. Functional and metabolic aspects of two different maturational stages.

Functional and metabolic parameters were compared in immature and mature megakaryocytes (MK) isolated from bone marrow of the mouse by Percoll density gradient centrifugation. Comparison of metabolic parameters revealed that the ability to take up serotonin was equal in both megakaryocytic fractions. The uptake of radioactively labeled adenine was increased in immature MK as compared with mature MK. Total adenosine triphosphate (ATP) content was enhanced during the differentiation from MK to platelets: immature MK: 5, mature MK: 29, platelets: 63 nmol ATP/mg protein. Since MK, like platelets, released ATP upon stimulation, thrombin-induced release was used as functional parameter to differentiate between secretable and non-secretable ATP compartments. Upon thrombin stimulation both MK fractions released about 25% of their total ATP as compared with about 40% secreted by platelets. Although the actual size of the non-secretable ATP pool was different in mature MK and platelets, they demonstrated similar percentages of retained ATP (20-25%) in contrast to a much higher retention (62%) by immature MK. The present findings suggest that the bulk of ATP is acquired by immature MK as they gain maturity, although some ATP is still obtained during even later stages of differentiation. This growing ATP pool could be attributed mainly to the enlargement of the secretable compartment during the transition of immature MK to mature MK.

Adenine↗
PubMed1983

Effects of endotoxin treatment on the differentiation of guinea pig megakaryocytes to blood platelets.

The effect of endotoxin treatment (30 micrograms/kg body weight) on megakaryocyte development and platelet production in guinea pigs was investigated. A moderate thrombocytopenia was noted at 24 h after endotoxin administration. Recovery was observed at 48 h when the platelet count had almost reached the normal level. A significant increase in platelet production was obtained at 48 h, indicated by an enhancement in incorporation of labelled sulphate into platelets and also by an increase in the number of circulating heavier platelets. Megakaryocytes were classified into different developmental stages - megakaryoblast, promegakaryocyte, megakaryocyte - using standard morphological criteria (size, shape of nucleus, nucleus/cytoplasm ratio). The number of mature megakaryocytes increased at 24 and 48 h after endotoxin treatment. It was possible to distinguish between two different types of mature megakaryocytes - early mature and mature megakaryocytes - by the presence of a methanol-sensitive acid phosphatase. This enzyme is found mainly in mature, presumably platelet-forming, megakaryocytes and in platelets. The increased number of mature megakaryocytes at 24 h was due to an enhancement in the number of early mature megakaryocytes, whereas the change at 48 h was due largely to an increased number of mature, platelet-forming megakaryocytes. Megakaryocytes were isolated from bone marrow of guinea pigs by Percoll density-gradient centrifugation and incubated with radioactively labelled leucine. Compared with the untreated controls megakaryocytes isolated 24 h after endotoxin treatment took up and incorporated higher amounts of leucine into protein, indicating a higher metabolic capacity of the early mature megakaryocytes. No alteration in the ploidy distribution of megakaryocytes was noted after endotoxin treatment.

Acid Phosphatase↗