Lithium and protein kinase C modulators regulate swelling-activated K-Cl cotransport and reveal a complete phosphatidylinositol cycle in low K sheep erythrocytes

C. M. Ferrell, P. K. Lauf, B. A. Wilson, N. C. Adragna

Research output: Contribution to journalArticlepeer-review

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 alternating 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.

Original languageEnglish (US)
Pages (from-to)81-93
Number of pages13
JournalJournal of Membrane Biology
Volume177
Issue number1
DOIs
StatePublished - Sep 1 2000
Externally publishedYes

Keywords

  • Cell swelling
  • Erythrocytes
  • K-Cl cotransport
  • Lithium
  • Phosphatidylinositol
  • Protein kinase C

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology

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