Comparative study of platelet dense granule constituents

Abstract

Cat, cattle, dog, horse, human, mink pig and rabbit platelets were separated from plasma by gel filtration. The gel-filtered plateltes (GFP) were treated with thrombin to induce maximal granule secretion and the potential dense granule constituents, ATP, ADP, serotonin (5-HT), Ca2+ and Mg2+, were measured in GFP and in the control and thrombin-treated platelets and in the respective supernatants. The amount of Ca2+, Mg2+, 5-HT, ATP and ADP within the nonreleasable pool for all species varied between 3.1 and 10.0 .mu.mol/1011 platelets for Ca2+ and Mg2+, was < 1.5 .mu.mol/1011 platelets for ADP and 5-HT and was between 2.0 and 5.0 .mu.mol/1011 platelets for ATP. Marked differences were observed in the releasable fraction. Human platelets were characterized by the largest releasable Ca2+ pool (> 10 .mu.mol/1011 platelets), the smallest secretable 5-HT and Mg2+ pool (< 0.5 .mu.mol/1011 platelets) and the lowest ATP-to-ADP ratio (> 1.0). Pig platelets had the highest amount of releasable Mg2+ (.apprx. 8.0 .mu.mol/1011 platelets). Rabbit platelets released the most 5-HT (> 3.0 .mu.mol/1011) and had the highest ATP/ADP (> 5.0). The releasable pool of Ca2+, Mg2+, ATP and ADP in the remaining species varied from .apprx. 1.5-4.0, .apprx. 1.0-3.0, 0.5-3.5 and .apprx. 0.5-1.5, .mu.mol/1011 platelets .mu.mol/1011 platelets, respectively.