Volume changes and whole cell membrane currents activated during gradual osmolarity decrease in C6 glioma cells: contribution of two types of K+ channels.
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 Ca(2+) dependent. In nominally Ca(2+)-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 Ca(2+) 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 Ca(2+) 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.
Ordaz
B
B
Department of Biophysics, National University of Mexico, Mexico City, Mexico.
Vaca
L
L
Franco
R
R
Pasantes-Morales
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D005910:Glioma / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013654:Taurine / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
D018118:Chloride Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013654:Taurine; D018698:Glutamic Acid; D002118:Calcium