title: The influence of hypotonicity on large-conductance calcium-activated potassium channels in human retinal pigment epithelial cells.
abstract: The aim of this study was to characterize the effects of hypotonicity on the activity of large-conductance Ca(2+)-activated K+ (BK(Ca)) channels in human retinal pigment epithelial (RPE R-50) cells. Effects of hypotonicity on ion currents were investigated with the aid of the patch-clamp technique. A regulatory volume decrease in response to a hypotonic solution (200 mOsm/L) was observed that could be blunted by paxilline. In whole-cell current recordings, a hypotonic solution (200 mOsm/L) reversibly increased the amplitude of K+ outward currents (I(K)). The increase of I(K) could be reversed by iberiotoxin (200 nM), paxilline (1 microM), or tetrandrine (5 microM), but not by glibenclamide (10 microM), disulphonic acid (DIDS) (100 microM), or dequalinium dichloride (10 microM). In RPE R-50 cells pretreated with thapsigargin, aristolochic acid, or pertussis toxin, the increased amplitude of I(K) in response to hypotonicity was unaltered. In cell-attached patches, an increase in BK(Ca)-channel activity was observed during hypotonicity-induced cell swelling. The enhanced channel activity elicited under this condition was mainly mediated by an increase in the number of long-lived openings. These findings support the evidence for the coupling of volume swelling to the functional activity of BK(Ca) channels.
authors.affiliation: Department of Ophthalmology, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan. sjsheu@isca.vghks.gov.tw
authors.forename: Shwu-Jiuan
authors.initials: SJ
authors.lastname: Sheu
authors.forename: Sheng-Nan
authors.initials: SN
authors.lastname: Wu
authors.forename: Dan-Ning
authors.initials: DN
authors.lastname: Hu
authors.forename: Jane-Fane
authors.initials: JF
authors.lastname: Chen
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D034341:Aristolochic Acids / Q000494:pharmacology; D044182:Benzylisoquinolines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D007038:Hypotonic Solutions / Q000737:chemistry / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology; D007783:Lactones / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009883:Ophthalmic Solutions / Q000737:chemistry / Q000494:pharmacology; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000378:metabolism / Q000493:pharmacokinetics; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D034341:Aristolochic Acids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D007038:Hypotonic Solutions; D007211:Indoles; D007783:Lactones; D009883:Ophthalmic Solutions; D010455:Peptides; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; C009438:tetrandrine; C048220:paxilline; D019284:Thapsigargin; C064719:iberiotoxin; C000228:aristolochic acid I; D037342:Pertussis Toxin; D011188:Potassium; D002118:Calcium