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Oxygen‐dependent K + fluxes in sheep red cells
Author(s) -
Campbell E. H.,
Gibson J. S.
Publication year - 1998
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.1469-7793.1998.679bv.x
Subject(s) - cotransporter , chemistry , extracellular , potassium , oxygen , intracellular , stimulation , biophysics , red cell , analytical chemistry (journal) , sodium , biochemistry , chromatography , biology , medicine , endocrinology , organic chemistry
1 This study was designed to investigate the O 2 dependence of K + influx in sheep red cells. Influx was determined using 86 Rb + as a tracer for K + ; glass tonometers coupled to a gas mixing pump were used to equilibrate cell samples to the requisite oxygen tension ( P O2 ). 2 Both volume‐ and H + ‐stimulated K + influxes in low potassium‐containing (LK) sheep red cells were approximately doubled on equilibration with O 2 relative to influxes measured in N 2 . O 2 ‐dependent influxes were abolished when Cl − was replaced with NO 3 − , consistent with mediation by the KCl cotransporter. At pH 7, P O2 required for half‐maximal stimulation was 56 ± 1 mmHg (mean ± s.e.m., 3 sheep) for the O 2 ‐dependent component of K + influx: thus P O2 values over the physiological range affected K + influx. 3 K + influx in fully deoxygenated sheep red cells showed substantial volume and H + sensitivity. These residual components in N 2 were also Cl − dependent, indicating that the KCl cotransporter of LK sheep red cells was active in the absence of O 2 . 4 Volume‐sensitive K + influxes in high potassium‐containing (HK) sheep red cells responded in a similar way to those in cells from LK sheep, although much smaller in magnitude, showing that intracellular [K + ] had no significant effect on the O 2 dependence of the cotransporter. 5 Intracellular [Mg 2+ ] ([Mg 2+ ] i ) was altered by incubating sheep red cells with A23187 (20 μM) and different values of extracellular [Mg 2+ ] ([Mg 2+ ] o ). Total [Mg 2+ ] i was determined by atomic absorption spectroscopy and free [Mg 2+ ] i from [Mg 2+ ] o and the Donnan ratio . Total [Mg 2+ ] i was 1.29 ± 0.08 mM (mean ± s.e.m., n = 5 ), similar to that reported in the literature. Estimates of free [Mg 2+ ] i showed an increase from 0.39 ± 0.05 in oxygenated cells to 0.52 ± 0.04 mM (mean ± s.e.m., n = 5 ; P < 0.05 ) in deoxygenated ones. 6 Finally, although K + influxes were altered by pharmacological loading or depletion of cells with Mg 2+ , the free [Mg 2+ ] i required to affect influxes significantly was outside the physiological range. Results are difficult to reconcile with P O2 modulating KCl cotransport activity directly via changes in free [Mg 2+ ] i or [Mg 2+ ‐ATP] i .