Heterogeneity of Storage Pool Deficiency

Abstract

Prolonged incubation of Storage Pool Deficient (SPD) platelets with 14C-5HT is followed by abnormally rapid catabolism of the amine. When a 1:1 mixture of normal and SPD platelets was incubated with 14C-5HT such abnormal metabolism was not detectable due to the compensatory effect of normal platelets. SPD or normal platelets were incubated with 2 μM 14C-5HT for 5 minutes, washed and resuspended in buffer. Addition of 20 μM imipramine was followed by a rapid efflux from SPD platelets of 14C-5HT, which was not degraded. Normal platelets were not affected. In mixtures of normal and SPD platelets treated with imipramine the efflux of 14C-5HT was proportional to the SPD platelet fraction and still evident when only 30% of SPD platelets were present. In three non-typical cases of congenital SPD no metabolism of exogenous 14C-5HT was observed. In two of these, platelets incubated with 14C-5HT, washed and treated with imipramine, showed a rapid efflux of 5HT, comparable to that seen in a 30% normal-70% abnormal mixture, suggesting that the defect only involves a part of the platelet population. In a third patient no efflux of 14C-5HT was seen after imipramine. Imipramine additiion to platelets preincubated with 14C-5HT appears to be a good way of distinguishing among different types of SPD and of investigating the presence of a similar defect in acquired SPD in which only a part of the platelet population is likely to be involved.