Erythrocyte membrane calcium transport in patients with primary hyperparathyroidism.

The chronic effect of PTH on erythrocyte membrane Ca transport was examined. (Ca+Mg)ATPase activity and passive Sr influx were measured to assess the rate of passive Ca influx (total and inhibited by dihydropyridines [DHPs]), in erythrocytes from patients with primary hyperparathyroidism and normal controls. Erythrocyte Sr influx was lower in patients, due to a decreased DHP-sensitive Sr influx. Conversely, efflux activity of (Ca+Mg)ATPase was not different in patients and controls. We hypothesize that in primary hyperparathyroidism chronic PTH stimulation may induce a downregulation of the erythrocyte Ca influx mediated by DHP-sensitive Ca carrier.