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O 2 ‐dependent K + fluxes in trout red blood cells: the nature of O 2 sensing revealed by the O 2 affinity, cooperativity and pH dependence of transport
Author(s) -
Berenbrink Michael,
Völkel Susanne,
Heisler Norbert,
Nikinmaa Mikko
Publication year - 2000
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.1469-7793.2000.t01-1-00069.x
Subject(s) - chemistry , ouabain , trout , cooperativity , cotransporter , extracellular , bohr effect , efflux , stereochemistry , biophysics , analytical chemistry (journal) , sodium , biochemistry , hemoglobin , chromatography , biology , oxygen–haemoglobin dissociation curve , organic chemistry , fishery , fish <actinopterygii>
1 The effects of pH and O 2 tension on the isotonic ouabain‐resistant K + (Rb + ) flux pathway and on haemoglobin O 2 binding were studied in trout red blood cells (RBCs) in order to test for a direct effect of haemoglobin O 2 saturation on K + transport across the RBC membrane. 2 At pH values corresponding to in vivo control arterial plasma pH and higher, elevation of the O 2 partial pressure ( P O2 ) from 7.8 to 157 mmHg increased unidirectional K + influx across the RBC membrane several‐fold. At lower extracellular pH values, stimulation of K + influx by O 2 was depressed, exhibiting an apparent p K a (p K′ a ) for the process of 8.0. Under similar conditions the p K′ a for acid‐induced deoxygenation of haemoglobin (Hb) was 7.3. 3 When trout RBCs were exposed to P O2 values between 0 and 747 mmHg, O 2 equilibrium curves typical of Hb O 2 saturation were also obtained for K + influx and efflux. However, at pH 7.9, the P O2 for half‐maximal K + efflux and K + influx ( P 50 ) was about 8‐ to 12‐fold higher than the P 50 for Hb‐O 2 binding. While K + influx and efflux stimulation by O 2 was essentially non‐cooperative, Hb‐O 2 equilibrium curves were distinctly sigmoidal (Hill parameters close to 1 and 3, respectively). 4 O 2 ‐stimulated K + influx and efflux were strongly pH dependent. When the definition of the Bohr factor for respiratory pigments (Φ=Δlog P 50 ×ΔpH −1 ) was extended to the effect of pH on O 2 ‐dependent K + influx and efflux, extracellular Bohr factors (Φ o ) of ‐2.00 and ‐2.06 were obtained, values much higher than that for Hb (Φ o = ‐0.49). The results of this study are consistent with an O 2 sensing mechanism differing markedly in affinity and cooperativity of O 2 binding, as well as in pH sensitivity, from bulk Hb.