Abnormal Erythrocyte and Renal Frusemide-Sensitive Sodium Transport in Idiopathic Calcium Nephrolithiasis

1. Anomalous transmembrane anion transport has been observed in erythrocytes of patients with idiopathic calcium nephrolithiasis.

2. To verify whether cation transport is also abnormal, we investigated the frusemide-sensitive Na⁺ efflux from Na⁺-loaded erythrocytes and the natriuretic response to acute intravenous frusemide administration in calcium oxalate renal stone formers.

3. Frusemide administration induced a statistically significant smaller increase in the fractional excretion of Na⁺ in patients than in control subjects. Abnormal kinetic properties of erythrocyte Na⁺-K⁺-2Cl⁻ co-transport were observed in approximately 60% of stone formers. The K_m for Na⁺ of Na⁺-K⁺-2Cl⁻ co-transport correlated with urinary Ca²⁺ excretion.

4. The abnormal kinetic properties of Na⁺-K⁺-2Cl⁻ co-transport may be relevant for stone formation, hampering renal Ca²⁺ reabsorption in the distal nephron and determining critical physicochemical conditions for calcium/oxalate crystallization.