Action of immobilized neuraminidase on the accumulation of 5-hydroxytryptamine by human platelets.

Abstract

Abstract The accumulation of 5-HT was studied in human platelets following graded desialylation with neuraminidase immobilized on macrobeads. Platelets were removed from the soluble sialylglyco-proteins of the plasma by gel filtration on Sepharose 2B; the uptake of 5-HT by gel filtered platelets over four hours was similar to that found using platelet rich plasma. Platelet aggregation induced by 10 −5 M 5-HT and 10 −6 M ADP was decreased following gel filtration and the use of Sepharose 2B insolubilized apyrase did not ameliorate this effect. Removal of up to 30 per cent of the platelet sialic acid, which results in changes in the glycoprotein pattern as demonstrated by two dimensional gel electrophoresis, appears to accelerate the rate of uptake of 5-HT. This is followed by a significantly decreased rate once 50% desialylation has been achieved. Native platelets and those from which 30 per cent of the sialic acid had been removed were refractory to resialylation with exogenous rat liver sialyltransferase though this enzyme preparation catalyses the resialylation of soluble asialoglycoprotein acceptor.