title: Swelling-activated anion channels are essential for volume regulation of mouse thymocytes.
abstract: Channel-mediated trans-membrane chloride movement is a key process in the active cell volume regulation under osmotic stress in most cells. However, thymocytes were hypothesized to regulate their volume by activating a coupled K-Cl cotransport mechanism. Under the patch-clamp, we found that osmotic swelling activates two types of macroscopic anion conductance with different voltage-dependence and pharmacology. At the single-channel level, we identified two types of events: one corresponded to the maxi-anion channel, and the other one had characteristics of the volume-sensitive outwardly rectifying (VSOR) chloride channel of intermediate conductance. A VSOR inhibitor, phloretin, significantly suppressed both macroscopic VSOR-type conductance and single-channel activity of intermediate amplitude. The maxi-anion channel activity was largely suppressed by Gd(3+) ions but not by phloretin. Surprisingly, [(dihydroindenyl)oxy] alkanoic acid (DIOA), a known antagonist of K-Cl cotransporter, was found to significantly suppress the activity of the VSOR-type single-channel events with no effect on the maxi-anion channels at 10 μM. The regulatory volume decrease (RVD) phase of cellular response to hypotonicity was mildly suppressed by Gd(3+) ions and was completely abolished by phloretin suggesting a major impact of the VSOR chloride channel and modulatory role of the maxi-anion channel. The inhibitory effect of DIOA was also strong, and, most likely, it occurred via blocking the VSOR Cl(-) channels.
authors.affiliation: Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan. psharapovna@yahoo.com
authors.forename: Ranokhon S
authors.initials: RS
authors.lastname: Kurbannazarova
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Bessonova
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Okada
authors.forename: Ravshan Z
authors.initials: RZ
authors.lastname: Sabirov
mesh_terms: D000200:Action Potentials; D000818:Animals; D002264:Carboxylic Acids / Q000494:pharmacology; D048429:Cell Size; D002712:Chlorides / Q000378:metabolism; D005682:Gadolinium / Q000494:pharmacology; D007192:Indenes / Q000494:pharmacology; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051379:Mice; D009997:Osmotic Pressure; D010693:Phloretin / Q000494:pharmacology; D060168:Thymocytes / Q000166:cytology / Q000378:metabolism* / Q000502:physiology
chemical_list: C059990:((dihydroindenyl)oxy)alkanoic acid; D002264:Carboxylic Acids; D002712:Chlorides; D007192:Indenes; D007473:Ion Channels; D005682:Gadolinium; D010693:Phloretin