Inhibition of Sulfhydryl-Dependent Platelet Functions by Penetrating and Non-Penetrating Anologues of Parachloromercuribenzene

The effects of PCMB and PCMBS on cation permeability, ADP aggregation, platelet volume and clot retraction have been studied in intact human platelets and have been compared to the effects of ouabain on the same functions. The influence of these agents on Mg^{+ +} -dependent ATPase activity and Na⁺, K⁺ activated ATPase activity of osmotically lysed platelets also has been evaluated. (a) Ouabain, which produces inhibition of Na^-, K⁺ dependent ATPase activity, has no influence on ADP-induced aggregation or clot retraction. (b) Both PCMB and PCMBS inhibit all ATPase activities in osmotically lysed platelets and inhibit ADP aggregation by intact platelets. Cysteine reverses the inhibition of ADP aggregation produced by both PCMB and PCMBS at a time when PCMB induced inhibition of clot retraction no longer is reversible. (c) Clot retraction is inhibited by the penetrating agent, PCMB, but is not affected by identical concentrations of PCMBS. These observations suggest that ADP aggregation and clot retraction are independent phenomena.