PHOSPHOLIPASE-C ACTIVITY IN PLATELETS FROM BERNARD-SOULIER SYNDROME PATIENTS

The levels of glycoprotein (GP) Ib and GPV and phospholipase C activit y were measured in platelets from three Bernard-Soulier syndrome patie nts. The patients' platelets had 46%, 46%, and 24% of control levels o f GPIbalpha and 43%, trace, and 13% of control levels of GPV as determ ined by immunoblot analysis. Stimulation by thrombin, trypsin, the thr omboxane analogue U46619, and the combination of U46619 and trypsin ca used the formation of [P-32]phosphatidic acid, an index of phospholipa se C activity, in [P-32] orthophosphate-prelabeled platelets. With all agonists, however, the formation of [P-32] phosphatidic acid was mark edly reduced in Bernard-Soulier syndrome platelets compared with contr ol platelets. These data indicated a postreceptor defect in phospholip ase C activation in Bernard-Soulier syndrome platelets and confirmed e arlier observations of potential proteolytic and nonproteolytic mechan isms of platelet activation.