title: Maxi K+ channel in apical membrane of vestibular dark cells.
abstract: Recordings were made on excised apical membrane patches from vestibular dark cells from the semicircular canal of gerbils to determine if ion channels could be involved in the process of K+ secretion. Both nonselective cation channels [Am. J. Physiol. 262 (Cell Physiol. 31): C1430-C1436, 1992] and K(+)-selective channels were found. The K+ channels occurred in only 0.7% of the patches. In symmetrical 145 mM KCl solutions, the current-voltage (I-V) relation of the K(+)-selective channel was linear, indicating the absence of rectification, and the conductance was 240 +/- 8 pS (n = 8). The Goldman-Hodgkin-Katz equation for current carried solely by K+ could be fitted to the I-V relation in asymmetrical K+ and Na+ solutions and yielded a K+ permeability of 5.78 x 10(-13) cm3/s (n = 12). The channel was shown to be impermeable to Li+, NH4+, N-methyl-D-glucamine, and Cl-. Channel activity increased with depolarization and with increasing free [Ca2+]; for voltages between +40 and -60 mV, the strongest regulation occurred in the range 10(-6) to 10(-5) M Ca2+. Tetraethylammonium (2 x 10(-2) M) had from the cytosolic side no effect on the open probability (Po) but completely inhibited activity from the extracellular side. Po was reduced by Ba2+ (5 x 10(-3) M), verapamil (10(-4) M), quinine (10(-4) M), and quinidine (10(-4) and 10(-3) M), while lidocaine (5 x 10(-3) M) had no measurable effect on Po but decreased the amplitude. Rb+ and Cs+ were either poorly permeable or partially blocked the channel in a voltage-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Biophysics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131.
authors.forename: S
authors.initials: S
authors.lastname: Takeuchi
authors.forename: D C
authors.initials: DC
authors.lastname: Marcus
authors.forename: P
authors.initials: P
authors.lastname: Wangemann
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D005849:Gerbillinae; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011336:Probability; D012665:Semicircular Canals / Q000166:cytology / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D004533:Egtazic Acid; D019789:Tetraethylammonium; D002118:Calcium