1. Volume changes and whole cell membrane currents activated during gradual osmolarity decrease in C6 glioma cells: contribution of two types of [K.sup.+] channels
- Author
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Ordaz, B., Vaca, L., Franco, R., and Pasantes-Morales, H.
- Subjects
Cells -- Research ,Biological sciences - Abstract
Volume changes and whole cell membrane currents activated during gradual osmolarity decrease in C6 glioma cells: contribution of two types of [K.sup.+] channels. Am J Physiol Cell Physiol 286: C 1399-C1409, 2004. First published January 21,2004; 10.1152/ajpcell.00198.2003.--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.sup.2+] dependent. In nominally [Ca.sup.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.sup.-] and [K.sup.+] currents showed activation at H-3% of an outwardly rectifying [Cl.sup.-] 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.sup.+] current with conductance of 4.1 nS, inhibited by clofilium but insensitive to the typical [K.sup.+] channel blockers. With 200 nM [Ca.sup.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.sup.+] current activated at H-l%, showing a rapid increase in conductance, suppressed by charybdotoxin and insensitive to clofilium. These results show the operation of two different [K.sup.+] channels in response to GOR in the same cell type, activated by [Ca.sup.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 C[l.sup.-] and amino acid osmosensitive pathways. The delayed amino acid efflux may contribute to counteract swelling at more stringent osmolarity reductions. volume regulation; taurine; hyposmolarity; isovolumetric regulation; regulatory volume decrease
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- 2004