Serotonin accumulation in granules of storage pool-deficient platelets of Chediak-Higashi cattle.

Platelets from cattle with the Chediak-Higashi (CH) syndrome are virtually devoid of dense granules, serotonin (5-HT), and stored ATP and ADP. The present study determined how the handling of 5-HT in normal cattle platelets differed from that in CH cattle platelets. Normal and CH platelets accumulated 5-[14C]HT to the same extent. After normal and CH platelets were incubated with 5-HT for 12 h most 5-HT is still intact, indicating that it was protected from metabolism. Part of the newly acquired 5-HT in normal and CH platelets was in a pool that was rapidly released by 5 U/ml of thrombin, suggesting that 5-HT was, in part, within granules. Subcellular fractionation studies showed that, whereas most of the newly acquired 5-HT in normal platelets was located in the dense granule fractions, about one fourth was found in the lighter granule fraction that was enriched in alpha-granules. The dense granule fraction was virtually absent in CH platelets, and most of the granule 5-HT was associated with the lighter granule fraction. The mixed granule fraction from CH platelets accumulated 5-HT but the uptake was about 10% of that from normal platelets. Unlike normal granules the uptake of 5-HT by CH granules was only slightly inhibited by reserpine but was reversed by NH4Cl and nigericin treatment.