Abstract
Routine clotting tests, general platelet function tests, platelet Na<sup>+</sup> and K<sup>+</sup> concentrations, the influx and efflux kinetics of <sup>86</sup>Rb<sup>+</sup> (as K<sup>+</sup> analogue) and the osmotic resistance have been studied in platelets from patients with a dominant hereditary macrocytic thrombopathic thrombocytopenia. Calculated on a cell-volume basis the pathological platelets showed no abnormalities in the concentration gradients for Na<sup>+</sup> and K<sup>+</sup>. In all patients a normal active uptake and a strikingly decreased passive efflux rate of <sup>86</sup>Rb<sup>+</sup> from the platelets was observed. Ouabain increased the efflux rate of <sup>86</sup>Rb<sup>+</sup> from control platelets, whereas no or weak efflux-increasing effect was observed in the pathological platelets. The platelets of all patients studied showed a shift towards a more resistant osmotic fragility curve, possibly caused by an increased surface to volume ratio of the cells. The findings are explained in terms of a pathological platelet membrane which is more rigid in structure and which requires more drastic stimuli in order to function properly.
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