Influence of pH on contact phase activation induced by negatively charged dialysis membrane. Platelet-poor plasma pools were diluted 1:20 in 0.9% saline (5% final plasma content). Pool pHs (measured at 37°C) were adjusted as indicated and perfused (single pass) through mini-hemodialysers constructed of AN69 membrane (250 cm2). At 4, 6, and 10 minutes of perfusion, aliquots of effluent plasma were immediately frozen in methanol/dry ice bath. Plasma kallikrein was determined by chromogenic assay using substrate S2302 (Biogenic, Maurin, France) after modification of a method described by De La Cadena et al.9 Means and standard deviations (error bars) of six experiments are shown. Kallikrein in the nonperfused pool remained at the baseline of less than 2 U/L over the course of the experiment. Kallikrein for plasma perfused over nonelectronegatively charged membranes (eg, cellulosic) remains at baseline of less than 2 U/L (data not shown). (□) pH 7.1; (•) pH 7.4; (▴) pH 7.6; (▿) pH 7.8.
