title: Block of inhibitory junction potentials and TREK-1 channels in murine colon by Ca2+ store-active drugs.
abstract: Post-junctional enteric inhibitory responses are composed of at least two components attributed to the release of a purine and nitric oxide (NO). The nitrergic component is characterized by membrane potential hyperpolarization; however, the conductances involved and the role of Ca(2+) stores in regulating these conductances are controversial. Conventional microelectrode recordings were performed in intact muscle strips and whole-cell voltage clamp experiments were performed on freshly dispersed cells and COS7 cells stably transfected with TREK-1 channels. Here we show that several Ca(2+) store-active compounds, including caffeine, ryanodine, and cyclopiazonic acid, reduce inhibitory junction potentials and responses to sodium nitroprusside in murine colonic muscles. We previously proposed that two-pore K(+) channels of the TREK family mediate a portion of the hyperpolarization response to NO in colonic muscles. We tested the effects of Ca(2+) store-active drugs in COS cells expressing murine TREK-1 channels and found these compounds block TREK-1 currents. These effects were greatly attenuated by dialysing cells with protein kinase A inhibitory peptide (PKAI). Caffeine also blocked stretch-dependent K(+) (SDK) channels, thought to be due to expression of TREK channels, in colonic myocytes, but these effects were not apparent in excised patches. Taken together our data show that Ca(2+) store-active compounds inhibit TREK-1 channels, native SDK channels, and nitrergic inhibitory junction potentials. These effects appear to be due, in part, to the cAMP/PKA stimulatory actions of these drugs and inhibitory effects of TREK channels.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA.
authors.forename: Sung Jin
authors.initials: SJ
authors.lastname: Hwang
authors.forename: Neil
authors.initials: N
authors.lastname: O'Kane
authors.forename: Cherie
authors.initials: C
authors.lastname: Singer
authors.forename: Sean M
authors.initials: SM
authors.lastname: Ward
authors.forename: Kenton M
authors.initials: KM
authors.lastname: Sanders
authors.forename: Sang Don
authors.initials: SD
authors.lastname: Koh
mesh_terms: D000818:Animals; D019556:COS Cells; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002522:Chlorocebus aethiops; D003106:Colon / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology*; D007365:Intercellular Junctions / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024683:Potassium Channels, Tandem Pore Domain / Q000187:drug effects* / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D024683:Potassium Channels, Tandem Pore Domain; C103742:potassium channel protein TREK-1; D012433:Ryanodine; D002110:Caffeine; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium; C000543:cyclopiazonic acid