Effect of phenazine methosulphate on K+ transport in human red cells.
The effect of phenazine methosulphate (PMS; 1 mM) on (86Rb+) K+ transport in human red cells was investigated to ascertain its action on the K+-Cl- cotransporter (KCC; defined as the Cl- dependent component of K+ flux measured in the presence of ouabain and bumetanide) and the Ca2+-activated K+ channel (Gardos channel; defined as the clotrimazole, 5 microM, -sensitive K+ flux). In the presence of Ca2+, both transport pathways were stimulated but effects were markedly greater under deoxygenated conditions (5-fold for KCC; 20-fold for the Gardos channel). KCC activation was inhibited by prior treatment with calyculin A (100 nM), implying action via protein dephosphorylation. Activation of the Gardos channel correlated with 28 +/- 3% inhibition of the plasma membrane Ca2+ pump, with maximal activity reduced from 7.7 +/- 1.1 to 2.7 +/- 0.7 micromol.(l cells.h)(-1) (all means +/- S.E.M. for n = 3), and a 3-fold increase in sensitivity of the channel to Ca2+ (EC50 reduced from 437 +/- 156 to 152 +/- 57 nM). Increased availability of NADH in deoxygenated conditions, resulting in increased free radical generation by PMS, may be responsible. We speculate that the similarity of the K+ transport phenotype produced by PMS to that seen in deoxygenated sickle cells is relevant to the pathophysiology of sickle cell disease.
Gibson
John S
JS
Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge, UK. jsg1001@cam.ac.uk
Muzyamba
Morris C
MC
Ellory
Clive J
CJ
D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D008773:Methylphenazonium Methosulfate / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*
D008773:Methylphenazonium Methosulfate; D010749:Phosphoprotein Phosphatases; D011188:Potassium; D002118:Calcium