Which parameters affect cytosolic free calcium in polymorphonuclear leukocytes of haemodialysis patients?

Background: Cytosolic free calcium ([Ca(2+)](i)) is an important second messenger during stimulation in a wide variety of cells, including polymorphonuclear leukocytes (PMNs). Its mobilization in PMNs is altered in various diseases such as atherosclerosis and ageing. In chronic haemodialysis (HD) patients, both atherosclerosis and accelerated ageing are well known. Therefore [Ca(2+)](i) in resting PMNs of HD patients was determined along with certain parameters which might affect it, such as recombinant human erythropoietin (rHuEpo) treatment, calcium-phosphate balance, and biocompatibility of dialysis membranes.

Methods: PMNs were separated by density centrifugation and [Ca(2+)](i) was determined by spectrofluorimetry using Quin 2/AM fluorescent dye. Laboratory parameters were determined by standard methods in clinical chemistry.

Results: It was found that [Ca(2+)](i) in resting PMNs of HD patients not undergoing rHuEpo therapy was higher than that of controls. After 12-weeks of rHuEpo therapy, [Ca(2+)](i) decreased to near normal level. The role of erythropoiesis in normalization of [Ca(2+)](i) in resting PMNs was supported by PMN [Ca(2+)](i) which was elevated in patients who had low haemoglobin (<100 g/l) or haematocrit (<0.30) values. In some patients, including those receiving rHuEpo treatment, [Ca(2+)](i) remained high, suggesting a role for other parameters in increasing [Ca(2+)](i). One possible parameter might be the disturbed calcium-phosphate metabolism of chronic renal failure, because we found a strong correlation between [Ca(2+)](i) and plasma iPTH levels in HD patients (r=0.743, P<0.001). [Ca(2+)](i) was also elevated in PMNs of those patients who had either low plasma calcium or high plasma phosphate levels. PMN [Ca(2+)](i) of HD patients correlated positively with the duration of HD (r=0.671, P<0.001). However, there was no correlation between [Ca(2+)](i) and patient age. The dialysis procedure itself also transiently increased PMN [Ca(2+)](i) HD patients, independently of the type of dialysis membrane.

Conclusion: PMN [Ca(2+)](i) is modulated by various parameters in HD patients, including the degree of anaemia, disturbances of calcium metabolism, and duration of dialysis treatment. The elevated [Ca(2+)](i) of resting PMNs might contribute to altered functions in these cells.