Biomedical subjects

A Blankenfeld

Publications and source records attributed to A Blankenfeld.

4 recordsLinked to original sources

PubMed1993

Platelet multielemental composition, lability, and subcellular localization.

Diagnostic X-ray spectrometry (DXS), based on X-ray fluorescence, was used to quantitate directly the multiple elemental composition of washed, intact human platelets (n = 16), with the following results: K = 3.08 +/- 1.00 mg/g, Ca = 1.18 +/- 0.29 mg/g, Zn = 35 +/- 9 micrograms/g. These values show that washed platelets contain significant pools of K, Ca, and Zn, the latter some 30-60-fold higher than plasma levels. Dialysis of whole platelets against cation exchange resin (Chelex-100) did not extract Ca(II) and Zn(II) sequestered within whole cells. To identify the subcellular locale of the elements, platelet lysate was subjected to 30-70% sucrose gradient ultracentrifugation and subcellular enriched fractions were obtained. Fractions were analyzed by DXS (for elements), electron microscopy (for dense granules), and subcellular markers fibrinogen and von Willebrand factor. In contrast to Ca and K, which accumulate in the dense granules and the cytoplasm, respectively, Zn appears to be distributed in the alpha-granules (40%) and the cytoplasm (60%). The subcellular distribution of Zn(II) is discussed within the context of the sensitivity of platelet response to the availability of Zn(II) and the platelet release reactions following stimulation.

Absorption↗

PubMed1993

Kinetic and mechanical parameters of pure and cryoprecipitate fibrin.

The kinetics of formation (clot time; CT) as well as a mechanical parameter (breaking strength; BS) of fibrin were measured at various concentrations of fibrinogen. In a pure system and for a fixed level of thrombin, the CT-fibrinogen dependency was biphasic, reaching a minimum in the range 1-8 microM fibrinogen. A new parameter, [Fib]min, the minimal fibrinogen concentration required for phase change, was derived from this. The [Fib]min values of pure fibrinogen activated with thrombin, ranged between 0.15 and 0.25 microM fibrinogen. Single donor cryoprecipitate (cryo) had similar kinetics and [Fib]min value. A technique for measuring the innate breaking strength of fibrin, independently of its adhesive properties, is described. For pure fibrin activated with thrombin, the BS was a linear function of fibrinogen concentration, with numeric values for the slope of 0.84 g/microM and slopeCa (with 2.5 mM Ca) of 2.26 g/microM, which transformed into a general description of the BS of fibrin and the fibrinogen level according to the equation: BS = mu [Fib]. The constants mu = 18.9 dyne/microM-cm2 and microCa = 55.7 dyne/microM-cm2 reflect the innate strength of fibrin clot per cross-section area. Cryo fibrin exhibited a BS equivalent to its fibrinogen level in a pure system. Although scanning electron microscopy of pure and cryo fibrin formed at equivalent fibrinogen levels revealed significant ultrastructural disparity between the pure and cryo fibrin, the kinetics of formation and the mechanical parameters of both were comparable.

Bleeding Time↗

PubMed1992

Model for the regulation of platelet volume and responsiveness by the trans-membrane Na+/K(+)-pump.

The correspondence between K+ uptake in platelets to their responsiveness was studied using 86Rb+ as an analogue of K+. An average 86Rb+ uptake rate of 0.73 (+/- 0.140) x 10(-15) mole Rb+/min-plt (n = 20) was observed. By the use of K(+)-influx inhibitors, we were able to distinguish three distinct 86Rb+ uptake pathways: an ouabain-sensitive (61% +/- 2% inhibitable) pump and two equivalent channels, only one of which is sensitive to furosemide. Other platelet parameters were also examined in conjunction with K(+)-uptake. Platelets incubated with ouabain exhibited an overall rise in their cell volume (MPV) with incubation time (delta MPV = 7.4 x 10(-17) L/min-1 plt-1). Concomitantly, over 24 hours, a steady decrease in platelet number was recorded by blood cell coulter, which correlated inversely with the counts of particles, which by their size resemble white blood cells (r = 0.89). On a cellular level, incubation with ouabain induced greater expression of surface fibrinogen-receptor (GPIIb), increased binding of FITC-labelled fibrinogen, and increased responsiveness to ADP. Our observations suggest the following sequence of events: Ouabain turns off the Na+/K(+)-ATPase pump, which leads to water accumulation in platelets and concomitant increased MPV. Greater expression of fibrinogen receptors on the distended platelet surface corresponds to spontaneous microaggregate formation as well as greater responsiveness to agonists. Our model links volume regulation, the expression of fibrinogen receptors, and the sensitivity of platelets to agonists to the activity of the Na+/K(+)-ATPase pump.

Blood Platelets↗

PubMed1991

Reducing white cells in platelet units.

White cells (WBCs) constitute a significant contaminant of platelet concentrates (PCs). Various technologies, including apheresis and filtration, are currently being developed to minimize the carryover of WBCs into platelets. The aim is to reduce contamination of less than 10(8) WBCs per platelet unit. As part of quality control monitoring of the blood bank operations, the centrifugation protocols employed in the preparation of platelet-rich plasma (PRP) have been evaluated for their impact on the WBC content of the PCs. The WBC content, which is expressed throughout the PRP volume as well as in the PC, reflects the degree of braking. For example, after centrifugation (2500 rpm, 4 min) of whole blood into packed red cells (RBCs) and PRP, braking-induced mixing increases the WBC content of the expressed PRP. Variations in the braking rates of the centrifuges used also correlate with the WBC carryover into packed platelets. An alternative centrifugation protocol to minimize WBC carryover is suggested. Whole blood is centrifuged at 2500 rpm for 1.5 minutes (rather than 4 min) and allowed to stop with no braking. This procedure adds some 3 minutes to the total centrifugation time, but the relative integral of this centrifugation program is approximately 50 percent smaller than that of the normally employed centrifugation protocol (with braking). It was observed that the WBC content throughout the expressed PRP, or in the entire PC, is reduced by about 75 percent. These results show that an effective method of significantly decreasing the WBC content of platelet units is simply to prepare PRP with reduced centrifugation time and with the braking programs disengaged.

Blood Platelets↗