Vanadate changes Ca2+ influx pathway properties in human red blood cells

The properties of the basal Ca2+ influx (measured using cells labelled with 45Ca2+) in intact human red blood cells (RBC) were compared with those of 45Ca2+ influx induced by vanadate. The basal Ca2+ influx was not sensitive to inhibitors of vanadate-induced Ca2+ influx such as the HS-reagent p-chloromercuribenzoate and low concentrations of Cu2+, and also the sensitivity to nifedipine was significantly weaker. High K+ known to suppress vanadate-induced 45Ca2+ influx had no effect on the basal Ca2+ influx. Both processes were saturated with Ca2+ but the latter was saturated at higher Ca2+ concentrations (KM(Ca) 2.1 vs. 0.5 mmol/l). These experiments favour the notion that vanadate changes the properties of the inward-directed Ca(2+)-transport pathway in human RBC membrane. Vanadate-induced 45Ca2+ influx was insensitive to pertussis toxin and cholera toxin, and several non-steroidal antiinflammatory agents did not influence it in a consistent manner. Li+ partly inhibited the 45Ca2+ uptake. Vanadate stimulated the incorporation of 32P(in) into PIP2 in human but not in pig RBC which are known to be defective in the phosphoinositide metabolism and in the vanadate-induced 45Ca2+ uptake. These results suggest that the change in the Ca2+ influx pathway properties induced by vanadate may involve changes in the metabolism of phosphoinositides but not of the arachidonate metabolism nor G-protein activation.