Increased cytosolic free sodium in platelets from patients with early-stage chronic renal failure

Cytosolic free sodium concentration ([Na+]t) and sodium transport systems were measured in intact platelets from 19 patients with early-stage chronic renal failure and 33 healthy control subjects using the novel fluorescent dye sodium-bindingbenzofuran- isophthalate. Resting [Na+] was significantly greater in patients with chronic renal failure compared to control subjects (40.8 ±3.1 mmol/1 versus 32.2 ± 2.0 mmol/1, mean±SEM, P<0.05). After inhibition of Na-K-ATPase by 1 mmol/1 ouabain a higher net sodium influx was observed in platelets from patients with chronic renal failure compared to control subjects (49.8 ±8.7 mmol/1 versus 28.5 ±5.2 mmol/1, P<0.05). The platelet Na-H exchanger was similar in the two groups. Cytosolic free calcium concentration ([Ca2+]j) was measured using fura2 and did not show significant differences between the two groups. To evaluate whether a circulating factor may be associated with elevated [Na+]b a linked-enzyme Na-K-ATPase assay was included. Compared to control subjects plasma from patients with chronic renal failure produced a significant inhibition of steady-state Na-K-ATPase activity by 11.2±3.0% (P<0.0). It is concluded that early-stage renal failure is associated with significant impairment of platelet sodium metabolism.