Abundance and activity of Ca2+-ATPase in hypercalciuric children

The plasma membrane Ca2+-ATPase (PMCA) is one of the main regulators of cel l Ca2+ homeostasis. The aim of our study was to determine whether the abund ance and activity of PMCA are altered in erythrocytes of children with idio pathic hypercalciuria. Twenty-four children with idiopathic hypercalciuria (13 girls and 11 boys, mean age 10.6+/-4.8 years; mean urinary calcium conc entration 0.85+/-0.20 mmol/mmol creatinine) and 30 healthy age-matched chil dren were enrolled. PMCA protein abundance was determined by Western blot a nalysis. Enzyme activity was determined spectrophotometrically. The abundan ce of PMCA did not differ in hypercalciuric patients from that of control s ubjects (98+/-22% vs 100+/-18%). Moreover, the activity was not different b etween the studied groups (3141+/-1494 vs 2953+/-780 nmol ATP/mg protein/h) . The extent of hypercalciuria did not correlate with enzyme abundance or a ctivity. Assuming that erythrocytes may reflect the renal tubular transport ing processes, our data suggest that other Ca2+-transport mechanisms than P MCA might be involved in the development of idiopathic hypercalciuria in ch ildren.