Effect of Ionic Calcium and Magnesium on Human Platelet Aggregation

Abstract

The ionic calcium requirement for platelet aggregation is much lower than that required for fibrin formation. Maximal aggregation can still take place with the [Ca2+] well below 5 × 10−6M. Chelation of Ca2+ with EGTA results in a decrease in aggregation at a higher [Ca2+] than when EDTA is employed. This seems to indicate that the [Ca2+]/[Mg2+] ratio may be of importance at low ionic concentrations. However, excess [Ca2+] and/or [Mg2+] above the normal levels inhibit aggregation. In fact, when both of these ions are added in excess of the normal levels their inhibitory effects are additive, indicating that the [Ca2+]/[Mg2+] ratio is of little consequence under these conditions.