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.
Division of Nephrology, Dialysis and Hypertension, San Raffaele Scientific Institute, University of Milan, Italy. soldati.laura@hsr.it
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L
Soldati
D
D
Adamo
S
S
Zerbi
A
A
Caumo
R
R
Spaventa
G
G
Bianchi
G
G
Vezzoli
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