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Titolo:
CYTOPLASMIC CALCIUM BUFFERS IN INTACT HUMAN RED-CELLS
Autore:
TIFFERT T; LEW VL;
Indirizzi:
UNIV CAMBRIDGE,PHYSIOL LAB,DOWNING ST CAMBRIDGE CB2 3EG ENGLAND
Titolo Testata:
Journal of physiology
fascicolo: 1, volume: 500, anno: 1997,
pagine: 139 - 154
SICI:
0022-3751(1997)500:1<139:CCBIIH>2.0.ZU;2-X
Fonte:
ISI
Lingua:
ENG
Soggetto:
BLOOD-CELLS; CA PUMP; INTRACELLULAR CALCIUM; POTASSIUM-TRANSPORT; HUMAN-ERYTHROCYTES; OLD INDIVIDUALS; CALMODULIN; CA-2+; K+; PERMEABILITY;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
42
Recensione:
Indirizzi per estratti:
Citazione:
T. Tiffert e V.L. Lew, "CYTOPLASMIC CALCIUM BUFFERS IN INTACT HUMAN RED-CELLS", Journal of physiology, 500(1), 1997, pp. 139-154

Abstract

1. Precise knowledge of the cytoplasmic Ca2+ buffering behaviour in intact human red cells is essential for the characterization of their [Ca2+](i)-dependent functions. This was investigated by using a refinedmethod and experimental protocols which allowed continuity in the estimates of [Ca2+](i), from nanomolar to millimolar concentrations, in the presence and absence of external Ca2+ chelators. 2. The study was carried out in human red cells whose plasma membrane Ca-2+ pump was inhibited either by depleting the cells of ATP or by adding vanadate to the cell suspension. Cytoplasmic Ca2+ buffering was analysed from plotsof total cell calcium content vs. ionized cytoplasmic Ca2+ concentration ([Ca-T](i) vs. [Ca2+](i)) obtained from measurements of the equilibrium distribution of Ca-45(2+) at different external Ca2+ concentrations ([Ca2+](o)), in conditions known to clamp cell volume and pH. The equilibrium distribution of Ca-45(2+) was induced by the divalent cation ionophore A23187. 3. The results showed the following. (i) The known red cell Ca2+ buffer represented by alpha, with a large capacity andlow Ca2+ affinity, was the main cytoplasmic Ca2+ binding agent. (ii) The value of alpha was remarkably constant; the means for each of fourdonors ranged from 0.33 to 0.35, with a combined value of all independent measurements of 0.34 +/- 0.01. (mean +/- S.E.M., n = 16). This contrasts with the variability previously reported. (iii) There was an additional Ca2+ buffering complex with a low capacity (similar to 80 mumol (340 g Hb)(-1)) and intermediate Ca2+ affinity (apparent dissociation constant, K-D,K-app approximate to 4-50 mu M) whose possible identity is discussed. (iv) The cell content of putative Ca2+ buffers withsubmicromolar Ca2+ dissociation constants was below the detection limit of the methods used here (less than 2 mu mol (340 g Hb)(-1)). 4. Vanadate (1 mM) inhibited the V-max of the Ca2+ pump in inosine-fed cells by 99.7%. The cytoplasmic Ca2+ buffering behaviour in these cells was similar to that found in ATP-depleted cells.

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Documento generato il 28/09/20 alle ore 11:31:47