Block of inhibitory junction potentials and TREK-1 channels in murine colon by Ca2+ store-active drugs.
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.
Hwang
Sung Jin
SJ
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA.
O'Kane
Neil
N
Singer
Cherie
C
Ward
Sean M
SM
Sanders
Kenton M
KM
Koh
Sang Don
SD
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*
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