Effects of trifluoperazine and membrane-bound sialic acid on 45Ca2+ uptake into erythrocytes.

After removal of more than 70% of the sialic acid from the erythrocyte membrane by treatment with neuraminidase, trifluoperazine (TFP) increased the rapid and slow phase of 45Ca2+ uptake into erythrocytes, identically to Ca2+ uptake into untreated erythrocytes from patients with tetanic syndrome. Both phases of 45Ca2+ influx were inhibited by extracellular Mg2+, Ki amounted to 4 mmol/l. However, the increased 45Ca2+ influx into patient erythrocytes in the presence of TFP was not caused by a reduced sialic acid content in the patients' erythrocytes. It was concluded that erythrocytes from patients with tetanic syndrome either bind more TFP or, if the same amount of TFP is bound, it has a stronger effect on 45Ca2+ influx.