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Oxygen‐dependent K + influxes in Mg 2+ ‐clamped equine red blood cells
Author(s) -
Campbell E. H.,
Cossins A. R.,
Gibson J. S.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.431ac.x
Subject(s) - cotransporter , chemistry , deoxygenation , oxygen , inorganic chemistry , biophysics , biochemistry , catalysis , sodium , biology , organic chemistry
1 Cl − ‐dependent K + ( 86 Rb + ) influxes were measured in oxygenated and deoxygenated equine red blood cells, whose free [Mg 2+ ] i had been clamped, to examine the effect on O 2 dependency of the K + ‐Cl − cotransporter. 2 Total [Mg 2+ ] i was 2.55 ± 0.07 mM (mean ± s.e.m., n = 6 ). Free [Mg 2+ ] i was estimated at 0.45 ± 0.04 and 0.68 ± 0.03 mM (mean ± s.e.m., n = 4 ) in oxygenated and deoxygenated red cells, respectively. 3 K + ‐Cl − cotransport was minimal in deoxygenated cells but substantial in oxygenated ones. Cl − ‐dependent K + influx, inhibited by calyculin A, consistent with mediation via the K + ‐Cl − cotransporter, was revealed by depleting deoxygenated cells of Mg 2+ . 4 Decreasing [Mg 2+ ] i stimulated K + influx, and increasing [Mg 2+ ] i inhibited it, in both oxygenated and deoxygenated red cells. When free [Mg 2+ ] i was clamped, Cl − ‐dependent K + influxes were always greater in oxygenated cells than in deoxygenated ones, and changes in free [Mg 2+ ] i of the magnitude occurring during oxygenation‐deoxygenation cycles had a minimal effect. Physiological fluctuations in free [Mg 2+ ] i are unlikely to provide the primary link coupling activity of the K + ‐Cl − cotransporter with O 2 tension. 5 Volume and H + ion sensitivity of K + influx in Mg 2+ ‐clamped red cells were increased in O 2 compared with those in deoxygenated cells at the same free [Mg 2+ ] i , by about 6‐ and 2‐fold, respectively, but again these features were not responsible for the higher fluxes in oxygenated cells. 6 Regulation of the K + ‐Cl − cotransporter by O 2 is very similar in equine, sheep and in normal human (HbA) red cells, but altered in human sickle cells. Present results imply that, as in sheep red cells, O 2 dependence of K + ‐Cl − cotransport in equine red cells is not mediated via changes in free [Mg 2+ ] i and that cotransport in Mg 2+ ‐clamped red cells is still stimulated by O 2 . This behaviour is contrary to that reported for human sickle (HbS) cells.