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Biomedical subjects

R J Haslam

Publications and source records attributed to R J Haslam.

At least 73 records · Page 4Linked to original sources
PubMed1976

Loss of sulfated proteoglycan from the surface of rabbit platelets during adenosine 5'-diphosphate-induced aggregation.

Rabbit platelets were labeled in vivo by intravenous injection of 35SO4=60 hours before the animals were exsanguinated. The labeled platelets were washed and resuspended in Tyrode's solution containing 0.35 per cent albumin. The aggregated normally upon the addition of ADP and during aggregation 14.0 +/- 2.7 per cent (mean +/- standard deviation) of the labeled material was lost into the suspending medium. The extent of loss was dependent on ADP concentration and was inhibited by inhibitors of ADP-induced aggregation (AMP, ATP, adenosine, prostaglandin E1, parachloromercuribenzensulfonate and lack of calcium). Since neither release of granule contents nor lysis occurs when rabbit platelets are aggregated by ADP, it was concluded that the labeled material that was lost had been part of the surface coat of the platelets. The labeled material has been identified in other studies as a proteoglycan in which the mucopolysaccharide is principally chondroitin sulfate A. Loss of this material did not make the platelets unresponsive to ADP. The platelets did not reincorporate labeled proteoglycan from plasma. Thrombin caused the release of 50 to 80 per cent of the total platelet-labeled material, presumably from both the granules and the surface. The functional significance of the loss of surface proteoglycan during platelet aggregation is unknown.

Adenosine Diphosphate↗
PubMed1974

Adenosine 3': 5'-cyclic monophosphate in young and senescent human fibroblasts during growth and stationary phase in vitro. Effects of prostaglandine E1 and of adrenaline.

Cyclic AMP levels per mg of cell protein were higher in late-passage (senescent) fibroblasts than in early-passage (young) fibroblasts both during growth and stationary phase, but, because the protein concentration per unit volume in senescent cells was lower than in young cells, the molar concentrations of intracellular cyclic AMP were very similar in the two cell types. In both young and senescent fibroblasts cyclic AMP levels declined during growth and no increase in intracellular cyclic AMP occurred in association with density-dependent inhibition of growth. These results indicate that changes in cyclic AMP concentration do not play a role in controlling the growth or in the senescent decline of human fibroblasts. Prostaglandin E(1) (1mum) caused maximal increases in fibroblast cyclic AMP concentration of 60-500-fold after 10-30min, and adrenaline (epinephrine) (10mum) caused maximum increases of 5-25-fold after 2-10min, depending on both the number of passages and the period after subculture. The cyclic AMP level in confluent young cells increased more with prostaglandin E(1) and far less with adrenaline than the cyclic AMP level in confluent senescent cells. During growth to confluence the cyclic AMP response to adrenaline declined in young cells and increased in senescent cells. As these responses to prostaglandin E(1) and to adrenaline changed independently of each other and of the basal cyclic AMP concentration, it is suggested that the expression of hormone receptors is altered both during growth to confluence and during senescence of human fibroblasts.

Adult↗
PubMed1967

The adenylate kinase of human plasma, erythrocytes and platelets in relation to the degradation of adenosine diphosphate in plasma.

1. Adenylate kinase (EC 2.7.4.3) has been shown to be present in human plasma obtained by conventional means and the adenylate-kinase activities of plasma and of lysed and intact human platelets and erythrocytes have been measured at 37 degrees by sensitive spectrophotometric methods. 2. The activities found in plasma ranged from 2.7 to 22.9mumoles of ADP formed/min./l. and in lysed platelets and lysed erythrocytes mean values of 0.79 and 12.0mumoles of ADP formed/min./10(9) cells respectively were found. Intact platelets and erythrocytes showed little or no activity. 3. The apparent K(m) of plasma adenylate kinase for ADP was found to be 1.4-1.6mm. 4. The adenylate-kinase activity of plasma was correlated with the free haemoglobin present and the larger part of the activity could be accounted for by haemolysis occurring either during the withdrawal of the blood or in vivo. 5. Aggregation of platelets by ADP, collagen fibres or thrombin released up to 16% of the platelet adenylate kinase into the suspending medium. 6. Measurement of the rate of breakdown of 1.6mum-ADP in plasma gave values of about 0.1mmu-mole/min./ml. This was not increased by addition of sufficient erythrocyte lysate to increase the activity of plasma adenylate kinase five to ten times. 7. It was concluded that the activity of adenylate kinase found in plasma, even after aggregation of the platelets, is insufficient to account for the rate of breakdown of low concentrations of ADP usually observed, and that another enzyme is responsible for this process.

Adenine Nucleotides↗