Further investigations on Bernard-Soulier platelet abnormalities.

Platelets from patients with the BSS make an interesting model for the study of 5-HT uptake, with their abnormal morphology including a defect in the plasma membrane GP I sialoglycoproteins (GP lb and glycocalicin), increased density in relation to an increased DB content, and increased size as a result of an abnormal shape change. The "apparent" kinetics of 5-HT incorporation by BSS platelets as measured with [3H]5-HT (0.2 to 2 micro M) were greatly modified: the VM was increased, but a high KM was needed. With a 5-HT concentration corresponding to the control platelet KM, twice as much 5-HT storage was taken up by BSS platelets as by normal platelets. The BSS platelets capacity for 5-HT storage as measure with [14C]5-HT (3 to 54 micro M) was increased up to to fivefold but normally inhibited b reserpine. The metabolism of platelet 5-HT was neither more rapid nor increased. The results, which further define the BSS platelet abnormalities, strongly suggest (1) a modification of the 5-HT transport process at the plasma membrane level and (2) an increased capacity of the platelets to accumulate 5-HT due to the increased DB content that parallels the increased platelet size. The possible relation between these two phenomena is discussed.