Platelet adhesion to human brain microvascular endothelial cells in vitro. Observation with video-enhanced contrast microscopy.

Employing video-enhanced contrast (VEC) microscopy and perfusion systems, we examined whether platelets adhere directly to human brain microvascular endothelial cells (HBEC) in vitro after thrombin treatment and whether adenosine diphosphate (ADP) or thromboxane A2-stimulated platelets adhere directly to HBEC at a low flow state in vitro. HBECs were cultured on a coverglass and put in the observation chamber of VEC microscopy. Following pretreatment with human alpha-thrombin 1.0 units/ml (n = 8) for 20 min, thrombin was thoroughly washed out. Platelet rich plasma (PRP) was perfused over HBEC at a low shear rate of 10 s(-1) for 30 min. Platelets adhered directly to thrombin-treated HBEC. Activated platelets by ADP (2 microM, n = 8) or thromboxane A2 (U-46619 10 microM, n = 5) were perfused over HBEC for 30 min and washed out. Platelets also adhered directly to HBEC. However, platelets did not adhere to HBEC when PRP only (n = 6) was perfused over HBEC for 30 min and washed out. Platelet adhesion directly to HBEC following thrombin treatment or platelet activation may play a pivotal role in secondary thrombus formation and microcirculatory disturbance in the ischemic brain.