The accelerating effect of calcium and other cations on the conversion of fibrinogen to fibrin

Whether the presence of calcium ions alters the rate at which fibrinogen is transformed to fibrin has been disputed repeatedly since Hammarsten first showed that solutions of thrombin clotted fibrinogen in the presence of oxalate salts (1). Most recently, Stefanini (2) reported that calcium salts inhibited the clotting of fibrinogen by thrombin. On the other hand, Seegers and Smith (3), Rosen-feld and Janszky (4), and Biggs and Macfarlane (5) offered evidence that calcium accelerated the conversion of fibrinogen to fibrin by thrombin. The problem was reexamined, using prepara-tions of plasma and fibrinogen which had been de-pleted of cations other than sodium through the use of ion exchange resins. Certain cations, in-cluding calcium, shortened the clotting time in all but the highest concentrations tested. The effects described could be demonstrated only when the ionic strength of the mixtures was maintained at a constant level, so that the action of specific ions could be differentiated from the influence of the total ionic strength of the medium. METHODS Plasma was prepared by centrifuging human blood for 10 minutes at 10,500 rpm. in a Sorvall SS-1 centrifuge (rim diameter 9 inches) at- 50 C., using lusteroid centri-fuge tubes coated with desicote (Beckman). The blood was drawn through a No. 18 needle, coated with tri (2-hydroxyethyl) dodecyl ammonium chloride,2 into a silicone-coated syringe. The supernatant plasma, ob-tained without the use of an anticoagulant, was shaken for 10 minutes with one-third its volume of Amberlite resin, IRC 50, which was in the sodium phase at pH 7.7. The resin was removed by centrifugation at room tem-perature for 10 minutes at 2,500 rpm in an Internationa