Calcium influx into red blood cells: the effect of sera from patients with systemic sclerosis.

The rheology of red blood cells in patients with systemic sclerosis is abnormal. To investigate this further we have examined the effect of sera from patients with systemic sclerosis on the handling of calcium ions by the erythrocyte membrane. Normal erythrocytes were filled with a photoprotein (aequorin) which emits light on contact with calcium. These photoprotein loaded normal erythrocytes were then incubated overnight with serum from: normal subjects (n = 20), from patients with systemic sclerosis (n = 27) or from patients with primary Raynaud's disease (n = 10). There was no significant difference in basal calcium leakage, as measured by the amount of light produced following the addition of triton X-100. Induced calcium influx, as measured by the amount of light produced following the addition of ionophore A23817, was significantly greater in the photoprotein loaded erythrocytes incubated overnight with serum from patients with systemic sclerosis compared to those incubated with serum from normal subjects (p less than 0.02) or patients with primary Raynaud's disease (p less than 0.01). This modulation of Ca2+ handling in erythrocytes by a serum factor from patients with systemic sclerosis could account for the alterations in erythrocyte function, such as red cell deformability, observed in systemic sclerosis.