Erythrocyte voltage-dependent calcium influx is reduced in hemodialyzed patients.
BACKGROUND
Uremia displays increased cytosolic free calcium ([Ca2+]i) in many different cell types, supporting the hypothesis of an altered Ca2+ transport modifying the functional activity of calcium signaling pathway.


METHODS
Thirty-five hemodialyzed patients and 20 age-matched subjects were studied. Erythrocyte resting [Ca2+]i and Ca2+ influx were measured by the fluorescent Ca2+-sensitive dye fura-2.


RESULTS
We found an increase of resting [Ca2+]i in erythrocytes from uremic hemodialyzed patients compared with matched healthy controls (103 +/- 2.5 nM, N = 20, vs. 90 +/- 4, N = 20, P < 0.01). Moreover, we found an altered voltage-dependent Ca2+ influx showing a reduced transport rate (0.42 +/- 0.03 nM/second vs. 0.74 +/- 0.08, P < 0.01). High levels of plasma parathyroid hormone (PTH) were related to augmented Ca2+ entry (r = 0.511, P < 0.05), contributing to maintain a high level of [Ca2+]i. Hemodialysis had no effect on cell calcium level and Ca2+ influx indices. The therapy with Ca2+ antagonists did not modify the values of resting [Ca2+]i or Ca2+ influx indices, but the correlation between PTH and influx indices was lost.


CONCLUSIONS
In conclusion, we found evidence for an alteration of erythrocyte Ca2+ influx caused by uremic toxicity that could be related to some organ disorders in uremia. The chronic increase of cellular calcium may contribute to influx derangement.
Soldati
L
L
Division of Nephrology, Dialysis and Hypertension, San Raffaele Scientific Institute, University of Milan, Italy. soldati.laura@hsr.it
Adamo
D
D
Zerbi
S
S
Caumo
A
A
Spaventa
R
R
Bianchi
G
G
Vezzoli
G
G
D000328:Adult; D002118:Calcium / Q000097:blood*; D016922:Cellular Senescence / Q000502:physiology; D004594:Electrophysiology; D004912:Erythrocytes / Q000378:metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D006435:Renal Dialysis; D014511:Uremia / Q000097:blood* / Q000628:therapy*
D010281:Parathyroid Hormone; D002118:Calcium