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Milton JG and Frojmovic MM. 1979. Invaginated plasma membrane of human platelets: Evagination and measurement in normal and giant platelets. J. Lab. Clin. Med. 93: 162-170. Full Article

A technique is described for estimating the amount of platelet plasma membrane. Addition of 80% by volume of distilled water to citrated human PRP converts platelets in the disc-form into large, spherical forms (spherocytes) without lysis in over 75% of these cells. Spherocyte formation is accompanied by about a twofold increase in mean surface area and a fourfold increase in the mean volume of the platelets. It is concluded that the large increase in surface area arises from an evagination of the platelet IM system. Spherocyte surface areas provide a measurement of total platelet plasma membrane surface area (including IM) which is in good agreement with recent electron microscope estimations of platelet plasma membrane. This technique is utilized to measure plasma membrane of platelets obtained from donors with a giant platelet syndrome (MPS) in which discocytes are normal-sized and shape-changed platelets are abnormally large. The observation that MPS platelets have a normal amount of plasma membrane suggests that the abnormally large size of these platelets arises because of a subtle flaw in the mechanism which regulates membrane reorganization during platelet shape change. Osmotic sphereocyte formation may be a rpaid and usefult technique for classifying giant platelet syndromes into 1) a group where the abnormally large platelet arises because of a defect in the way plasma membrane is organized and 2) a group where the abnormally large size is associated with increased plasma membrane. The significance of this kind of observation for the etiology of giant platelet syndromes is discussed.

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