title: Functional evidence for Na+-activated K+ channels in circular smooth muscle of the opossum lower esophageal sphincter.
abstract: Na(+) reduction induces contraction of opossum lower esophageal sphincter (LES) circular smooth muscle strips in vitro; however, the mechanism(s) by which this occurs is unknown. The purpose of the present study was to investigate the electrophysiological effects of low Na(+) on opossum LES circular smooth muscle. In the presence of atropine, quanethidine, nifedipine, and substance P, conventional intracellular electrodes recorded a resting membrane potential (RMP) of -37.5 +/- 0.9 mV (n = 4). Decreasing [Na(+)] from 144.1 to 26.1 mM by substitution of equimolar NaCl with choline Cl depolarized the RMP by 7.1 +/- 1.1 mV. Whole cell patch-clamp recordings revealed outward K(+) currents that began to activate at -60 mV using 400-ms stepped test pulses (-120 to +100 mV) with increments of 20 mV from holding potential of -80 mV. Reduction of [Na(+)] in the bath solution inhibited K(+) currents in a concentration-dependent manner. Single channels with conductance of 49-60 pS were recorded using cell-attached patch-clamp configurations. The channel open probability was significantly decreased by substitution of bath Na(+) with equimolar choline. A 10-fold increase of [K(+)] in the pipette shifted the reversal potential of the single channels to the positive by -50 mV. These data suggest that Na(+)-activated K(+) channels exist in the circular smooth muscle of the opossum LES.
authors.affiliation: Div. of Gastroenterology, Hotel Dieu Hospital, 166 Brock St., Kingston, ON, Canada.
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: William G
authors.initials: WG
authors.lastname: Paterson
mesh_terms: D000818:Animals; D002794:Choline / Q000378:metabolism; D048293:Didelphis; D049630:Esophageal Sphincter, Lower / Q000378:metabolism*; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D009119:Muscle Contraction; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D015221:Potassium Channels; D012964:Sodium; D002794:Choline; D011188:Potassium