Volume changes and whole cell membrane currents activated during gradual osmolarity decrease in C6 glioma cells: Contribution of two types of K + channels

B. Ordaz, L. Vaca, R. Franco, H. Pasantes-Morales

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

Volume changes and whole cell ionic currents activated by gradual osmolarity reductions (GOR) of 1.8 mosM/min were characterized in C6 glioma cells. Cells swell less in GOR than after sudden osmolarity reductions (SOR), the extent of swelling being partly Ca2+ dependent. In nominally Ca2+-free conditions, GOR activated predominantly whole cell outward currents. Cells depolarized from the initial -79 mV to a steady state of -54 mV reached at 18% osmolarity reduction [hyposmolarity of -18% (H-18%)]. Recordings of Cl- and K+ currents showed activation at H-3% of an outwardly rectifying Cl- current, with conductance of 1.6 nS, sensitive to niflumic acid and 5-nitro-2-(3-phenylpropylamino)benzoic acid, followed at H-18% by an outwardly rectifying K+ current with conductance of 4.1 nS, inhibited by clofilium but insensitive to the typical K+ channel blockers. With 200 nM Ca2+ in the patch pipette, whole cell currents activated at H-3% and at H-13% cells depolarized from -77 to -63 mV. A K+ current activated at H-1%, showing a rapid increase in conductance, suppressed by charybdotoxin and insensitive to clofilium. These results show the operation of two different K+ channels in response to GOR in the same cell type, activated by Ca2+ and osmolarity and with different osmolarity activation thresholds. Taurine and glutamate efflux, monitored by labeled tracers, showed delayed osmolarity thresholds of H-39 and H-33%, respectively. This observation clearly separates the Cl- and amino acid osmosensitive pathways. The delayed amino acid efflux may contribute to counteract swelling at more stringent osmolarity reductions.

Original languageEnglish (US)
Pages (from-to)C1399-C1409
JournalAmerican Journal of Physiology - Cell Physiology
Volume286
Issue number6 55-6
DOIs
StatePublished - Jun 2004

Keywords

  • Hyposmolarity
  • Isovolumetric regulation
  • Regulatory volume decrease
  • Taurine
  • Volume regulation

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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