(Ca+Mg)ATPase and calcium influx in eruthrocytes of patients with idiopathic hypercalciuria

Increased erythrocyte (Ca+Mg)ATPase activity was previously observed in idiopathic hypercalciuria. In order to verify if this alteration is a primary or a secondary event, we studied Sr influx in erythrocytes from subjects with idiopathic hypercalciuria. (Ca+Mg)ATPase activity was significantly higher in hypercalciuric than in hypercalciuric than in normocalciuric subjects whereas no difference in Sr influx was found between the two groups. (Ca+Mg)ATPase activity positively correlated with the erythrocyte Sr content found after 5 min of incubation and with urine Ca excretion. The normal Sr permeability suggests that (Ca+Mg)ATPase is primarily altered in idiopathic hypercalciuria. The primary increase of (Ca+Mg)ATPase activity may enhance passive Ca influx by reduction of cellular Ca concentration. It may induce a defect in cellular Ca metabolism that may cause idiopathic hypercalciuria by stimulating bone Ca turn-over and enteral Ca absorption.