Platelet plasma membrane changes in human type IIa hypercholesterolemia.

We have examined platelets collected from hypercholesterolemic (HC) young patients (n = 12) and from normocholesterolemic young volunteers (n = 9) by means of freeze fracture. The mean value of the surface density per square micrometer of the openings of the surface-connected canalicular system was significantly higher (p less than 0.03) in the HC patients (2.4 +/- 0.6) compared with the controls (1.8 +/- 0.5). It was also positively correlated with the low-density lipoprotein cholesterolemia/total cholesterol ratio (p less than 0.005) and inversely correlated with the high-density lipoprotein cholesterolemia/total cholesterol ratio (p less than 0.01). These data indicate that the circulating platelets of HC type IIa patients appear changed at ultrastructural level and that their modification may be somehow related to the atherogenetic processes.