Lithium and Protein Kinase C Modulators Regulate Swelling-Activated K-Cl Cotransport and Reveal a Complete Phosphatidylinositol Cycle in Low K Sheep Erythrocytes |
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Authors: | CM Ferrell PK Lauf BA Wilson NC Adragna |
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Institution: | (1) Department of Pharmacology and Toxicology, Wright State University, Dayton, Ohio 45435, USA, US;(2) Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45435, USA, US;(3) Department of Biochemistry and Molecular Biology, Wright State University, Dayton, Ohio 45435, USA, US |
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Abstract: | K-Cl cotransport (COT), a ouabain-insensitive, Cl-dependent bidirectional K flux, is ubiquitously present in all cells, plays
a major role in ion and volume homeostasis, and is activated by cell swelling and a variety of chemical interventions. Lithium
modulates several cation transport pathways and inhibits phospholipid turnover in red blood cells (RBCs). Lithium also inhibits
K-Cl COT by an unknown mechanism. To test the hypothesis whereby Li inhibits swelling-activated K-Cl COT by altering either
its osmotic response, its regulation, or by competing with K for binding sites, low K (LK) sheep (S) RBCs were loaded with
Li by Na/Li exchange or the cation ionophore nystatin. K-Cl COT was measured as the Cl-dependent, ouabain-insensitive K efflux
or Rb influx. The results show that Li altered the cell morphology, and increased both cell volume and diameter. Internal
(Li
i
) but not external (Li
o
) Li inhibited swelling-activated K-Cl COT by 85% with an apparent K
i
of ∼7 mm. In Cl, Li
i
decreased K efflux at relative cell volumes between 0.9 and 1.2, and at external pHs between 7.2 and 7.4. Li
i
reduced the V
max
and increased the K
m
for K efflux in Cl. Furthermore, Li
i
increased the production of diacylglycerol in a bimodal fashion, without significant effects on the phosphatidylinositol
concentration, and revealed the presence of a complete PI cycle in LK SRBCs. Finally, phorbol ester treatment and PD89059,
an inhibitor of mitogen-activated protein kinase (ERK2) kinase, caused a time-dependent inhibition of K-Cl COT. Hence, Li
i
appears to inhibit K-Cl COT by acting at an allosteric site on the transporter or its putative regulators, and by modulation
of the cellular phospholipid metabolism and a PKC-dependent regulatory pathway, causes an altered response of K-Cl COT to
pH and volume.
Received: 1 November 1999/Revised: 6 June 2000 |
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Keywords: | : Lithium — K-Cl Cotransport — Phosphatidylinositol — Erythrocytes — Protein kinase C — Cell Swelling |
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