Platelet basal cytosolic calcium: The influence of plasma factors in cirrhosis

Background: Platelet cytosolic calcium is necessary for normal platelet function, and may reflect intracellular signalling in vascular smooth muscle cells, Methods: The cytosolic calcium of platelets from patients with cirrhosis and control subjects was measured in contact with plasma from either source, using FURA 2AM. Results: The basal cytosolic calcium of patients with cirrhosis was found to be significantly lower than that of control subjects (95.7 +/- 10.0 cf. 128.0 +/- 7.8 nmol/l; p = 0.02), When platelets from control subjects were incubated for 45 min with freshly obtained plasma from patients with cirrhosis, the control platelet cytosolic calcium fell to concentrations similar to those of patient platelets (93.0 +/- 7.8 nmol/l; p < 0.005). Such an effect was not observed if patient serum or plasma that had previously been frozen was used, When patient platelets were incubated with fresh control subject plasma, the platelet cytosolic calcium increased (165.4 +/- 19.9 nmol/l; p = 0.01). Conclusion: These results indicate that a plasma-borne factor, sensitive to freezing, is responsible for the abnormalities of platelet calcium signalling noted in cirrhosis.