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The main purpose of this experiment was to assess the functional importance of platelet membrane amino groups (NH2). Picryl Sulfonic Acid (PSA) is a known NH2 modifier. Platelets were harvested, exposed to 0.25 - 32 mM PSA for 15 minutes at 22°C. They were then washed and functionally tested. The release was measured by C5HT release. The release reaction was induced by 0.1, 1, and 10 u/ml Thrombin (THR), Trypsin (TRY), Collagen (COL), and Latex particles (LAT). There was gradual but never complete inhibition of the release reaction. At 16 mM PSA, the platelets started to lose small amounts of 5HT (4%). Clot retraction was not affectedby 1 to 32 mil PSA. 5HT uptake was enhanced at 0.1 to 4 mM PSA (paired t test, p&lt;0.01) and maximal at 2 mM PSA.Pre-incubation with 0.25 and 0.5 mM PSA in the presence of calcium enhanced the PSA effect on rate of 5HT uptake (paired t test, p&lt;0.01). This may be due to the enhanced availability of amino groups to PSA in the presence of Ca, speculated by Godin to be due to a lipid effect (1972). Incorporation of PSA into the membrane was increased in the presence of Ca (O.D. at 335 nm). In summary, PSA modification of platelet membrane NH2 groups partially but never completely interferes with the induction of the release reaction. The inhibition was not specific with respect to the release inducing agent. Clot retraction remains intact. The observed significant enhancement in rate of 5HT uptake may be specific or may be due to neutralization of the charge on free amino groups, which repels 5HT.

Enhancement of 5HT Uptake by Picryl Sulfonic Acid Amino Group Modification in the Platelet Membrane