THE SIGNIFICANT ENHANCEMENT OF FIBRINOLYSIS BY CALCIUM-ION IN A CELL-FREE SYSTEM - THE SHORTENING OF EUGLOBULIN CLOT LYSIS TIME BY CALCIUM-ION

We investigated the roles of calcium ion (Ca2+) on euglobulin clot lys is time (ECLT) and found that the physiological concentration of Ca2significantly (4-5 times) shortened ECLT. The shortening was observed at the concentration of Ca2+ higher than 1.5-2.0 mM. Other divalent ca tions such as Mg2+, Zn2+ or Mn2+ didn't change ECLT. Anti-tPA antibody or plasminogen activator inhibitor-1 prolonged ECLT in the absence of Ca2+, whereas they had no effect on ECLT shortened by Ca2+. C1 inacti vator also had no effect. When barium absorbed plasma was employed, th e shortening of ECLT by Ca2+ wasn't observed, whereas it was recovered by the readdition of barium absorbed fraction. When factor X deficien t plasma was employed, the shortening of ECLT by Ca2+ was also not obs erved. Thus, Ca2+ enhances fibrinolysis in a cell free system by a nov el pathway in which the presence of factor X is prerequisite.