Influence of human plasma or serum albumin on ADP- or vasopressin-induced calcium increases in human platelets

Abstract

By focusing the consequences of loading platelets with the fluorescent calcium indicator, fura-2, in buffer or plasma the influences of plasma constituents on calcium responses in blood platelets has been worked out. Proteins were removed from the pre-incubation medium before agonist stimulation and measurement of intracellular calcium concentration [Ca2+]i. We found that moderate amounts (1-33%, v/v) of plasma added to the buffer during pre-incubation stimulated the mobilization of cytoplasmic calcium, delta[Ca2+]i, and reduced the time from agonist stimulation to peak level of [Ca2+]i in platelets stimulated with ADP or arginine vasopressin A8VP. With the buffer used, calcium response was restored by addition of 33% (v/v) plasma to the same level as found for unwashed platelets in the platelet rich plasma (cf. methods). The presence of human serum albumin during the pre-incubation also influenced the calcium response, but not to the same extent as plasma. From a resting level of 73 +/- 10 nmol l-1, addition of 0.4 mumol l-1 ADP increased the [Ca2+]i by 24 +/- 13 nmol l-1 (n = 20), 65 +/- 30 nmol l-1 (n = 5), and 144 +/- 44 nmol l-1 (n = 22) in platelets pre-incubated with buffer, 5 gl-1 albumin, and 33% (v/v) plasma, respectively. The corresponding values after stimulation with 0.05 mumol l-1 A8VP were 49 +/- 34 nmol l-1, 105 +/- 27 nmol l-1, and 170 +/- 39 nmol l-1, (n = 7). In platelets incubated in buffer only, the delta t from stimulation with 0.4 mumol l-1 ADP was 18.9s.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin uptake stimulating peptide found in plasma of normal individuals and in some autistic urines

“…Platelet preparation has been described (4, 5). Briefly, blood was drawn by cubital venepuncture from healthy males into vacutainers with 1/6th the volume of citric acid/dextrose (65 m m citric acid, 85 m m Na‐citrate, 111 m m glucose), made as described (4). Platelet‐enriched plasma (PRP) was obtained by centrifugation at 1000 g for 5 min at 20°C.…”

“…The suspension was kept in stoppered polyethylene tubes prior to use for 1–3 h at room tempe0rature and shielded from light. If the suspension was cooled in ice the platelet membranes become leaky to fura‐2 (4, 5).…”

“…Thus, the cloned serotonin 5‐HT 2a receptor has the same primary structure in the frontal cortex and in human platelets (2) and the uptake and release of serotonin seems similar (1). Because plasma modulates the intracellular calcium mobilization caused by ADP and vasopressin (3–5), we have tried to characterize some of the low molecular weight compounds involved in this modulation. We describe here the isolation and characterization of a small peptide from plasma that increases the uptake of serotonin (5‐HT) into platelets.…”

Beyond COX-1: the effects of aspirin on platelet biology and potential mechanisms of chemoprevention

“…The most discussed modification of serum albumin in the literature focuses on the acetylation of lysine residues [ 22 , 50 ]. Human serum albumin has also been observed to affect platelet-clotting mechanisms by influencing calcium regulation [ 100 ].…”

Characterization of a unique dihydropyrimidinone, ethyl 4-(4′-heptanoyloxyphenyl)-6-methyl-3,4-dihydropyrimidin-2-one-5-carboxylate, as an effective antithrombotic agent in a rat experimental model

“…These observations suggested the direct stimulatory action of Ca 2+ ‐channel blockers on endothelial NO production. Normally, cytosolic Ca 2+ is kept very low (10 −7 m ) by the action of Ca 2+ pumps in the endoplasmic reticulum, mitochondria, and plasma membrane while ADP, collagen and thrombin increase Ca 2+ concentration in cytosol, which is obliterated by H‐DHPM [20–23] . Intercellular calcium communication (ICC) is a widespread form of cell–cell communication that allows tissue coordination of cell proliferation, differentiation, and metabolism.…”