title: Outward K+ current in epithelial cells isolated from intermediate portion of endolymphatic sac of guinea pigs.
abstract: Ion currents in epithelial cells isolated from the intermediate portion of endolymphatic sac (ES) in guinea pigs were investigated with the use of the whole cell patch-clamp technique. Depolarizing voltage steps from a holding potential of -60 mV induced a time- and voltage-dependent outward current, which is comparable to that of delayed rectifying K+ currents. The average resting membrane potential in the current-clamp mode was -54.8 +/- 11 mV (n = 45), which was similar to the value of zero current potential (-55.6 +/- 0.8 mV, n = 32) obtained from current-voltage (I-V) relationships of outward currents in voltage-clamp mode. The I-V relationship of the tail current exhibited a reversal potential (Erev) of -78.1 +/- 0.9 mV (n = 19) in standard external solution. The Erev of the outward current was linearly related to the logarithm of extracellular K+ concentrations. The slope was 48 mV per 10-fold change in extracellular K+ concentrations. The time constants of K+ current activation, inactivation, and K+ tail current deactivation were voltage dependent. The steady-state activation and inactivation of K+ current exhibited a sigmoidal relationship to voltage. The 50% maximal activation voltage and slope factor were -21 and 11 mV (n = 8), respectively. The 50% maximal inactivation voltage and slope factor were -45 and 13 mV (n = 7), respectively. The K+ current was blocked by externally applied 1 mM 4-aminopyridine (4-AP), 5 mM Ba2+ and 20 mM tetraethylammonium chloride (TEA). The sensitivity of the current to 4-AP and Ba2+ was higher than that to TEA. Elimination of external Ca2+ and increase of internal Ca2+ failed to significantly change the current, suggesting that the K+ current may be Ca2+ independent. The results show that epithelial cells in the intermediate portion of the ES possess a delayed-rectifier K+ current, which may be involved in membrane stability or in the ion balance between the cytosol and the extracellular environment.
authors.affiliation: Department of Otolaryngology, Kagawa Medical University, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Wu
authors.forename: N
authors.initials: N
authors.lastname: Mori
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004848:Epithelium / Q000502:physiology; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D008208:Lymphatic System / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D015221:Potassium Channels / Q000502:physiology*; D013997:Time Factors
chemical_list: D015221:Potassium Channels; D011188:Potassium