The increase of openings of the surface-connected canalicular system in weekly stimulated platelets is prevented by a carbochromen derivative. A computerized morphometric analylis of freeze-etched human platelets plasma-membrane

When thrombin is added to platelet rich plasma at very low concentrations (0.02 U/ml), platelets undergo an activation process. Under these conditions platelets discharge beta-thromboglobulin, platelet factor 4 and the "platelet derived growth factor". In this paper we present evidence that when human platelets are weakly stimulated with thrombin, the number of openings of the surface connected canalicular system (SCCS) increases. Analogous SCCS increase was observed in hypercholesterolemic rabbits as well in humans (familial hyperchoelsterolemia). 8-chlorocarbochromen (AD6), an antiaggregating drug, inhibits the SCSS in vitro increase while acetylsalicylic acid was uneffective.