Red blood cell calcium level in chronic renal failure: Effect of continuous ambulatory peritoneal dialysis

Red blood cell (RBC) calcium, calcium 45 influx, and calcium extrusion as indicated by Ca-stimulated, Mg-dependent adenosine triphosphatase (CaATPase) was determined in patients with chronic renal failure (CRF), patients with CRF receiving continuous ambulatory peritoneal dialysis (CAPD) treatment, and controls. Cell calcium, which in the controls was 5.5 μmol/L of cells, was elevated in patients with CRF - 30.6 ± 6.8 μmol/L of cells (p < 0.002) - and in patients receiving CAPD - 23.6 ± 6.7 μmol/L cells (p < 0.02. Basal CaATPase activity in controls was 850.7 ± 66.7 nmol inorganic phosphate per milligram of protein per hour. It was suppressed in patients with CRF and patients receiving CAPF: 504.9 ± 34.4 nmol inorganic phosphate per milligram of protein per hour and 618.2 ± 47.3 nmol inorganic phosphate per milligram of protein per hour, respectively (p < 0.01). Calmodulin-stimulated CaATPase revealed a pattern similar to that of CaATPase basal activity. RBC calcium showed an inverse correlation with CaATPase activity ( r = -0.935, p < 0.005) in patients with CRF. Calcium influx was increased in patients with CRF and in patients receiving CAPD: 12.00 ± 1.34 μmol/L of cells per hour and 13.60 ± 1.70, respectively, compared with 4.61 ± 0.39 μmol/L of cells per hour in controls (p < 0.001). Patients with CRF have elevated RBC calcium levels mainly related to decreased extrusion and to increased influx. CAPD fails to improve substantially these abnormalities. Plasma vanadium levels were markedly elevated in patients undergoing hemodialysis and marginally in patients receiving CAPD. This inhibitor of CaATPase did not change by hemodialysis and did not correlate with CaATPase in any of the five groups in which it was tested.