Prostaglandin E-1-induced deconsolidation of thrombin-activated platelet aggregates I: Ultrastructure-computer image analysis

We have compared, at an ultrastructural-computer image morphometric level, the relaxation induced by Mg-ethylene-bis-oxyethylenenitrilo-tetracetic aci d and prostaglandin E-1 on a model of a thrombin-activated platelet aggrega te. Mg-ethylene-bisoxyethylenenitrilo-tetracetic acid produced a small incr ease of 5.0% of the intercellular space over the control levels, and a decr ease of 10.0+/-1.3% of the cross-sectional area of the platelets, with no a pparent cytoskeletal alterations. In contrast, the prostaglandin E-1-treate d preparation shows a 360% increase in the intercellular space and a decrea se of the average platelet cross-sectional area of 30.0+/-2.0% with marked cytoskeletal alterations. We use the term "deconsolidation" to describe thi s effect. The enlargement of the intercellular space allows the observation of two types of contacts: (1) a type S (segmental) complex, of approximate ly 200-nm length that maintains a narrow interplatelet gap of 20-30 nm, fil led with a dense intercellular material, and (2) a type R (reticular) compl ex, formed by scant focal regions of the plasma membrane from opposing plat elets that are connected through a mesh of fibrillar or granular material c ontained within a variable-size space. We hypothesize that deconsolidation is caused by fluid loss from the platelets into the intercellular space. As a result, platelet volume decreases and intercellular space increases. (C) 1999 Elsevier Science Ltd. All rights reserved.