title: Ammonium ion enhances the calcium-dependent gating of a mammalian large conductance, calcium-sensitive K+ channel.
abstract: We observed that the current amplitude and activation of expressed, mouse brain large conductance, calcium-sensitive K+ channels (BKCa channels) may be reversibly enhanced following addition of low concentrations of the weakly permeant cation NH4+ to the cytoplasmic face of the channel in excised, inside-out membrane patches from HEK 293 cells. Conductance-voltage relations were left-shifted along the voltage axis by addition of NH4Cl in a concentration-dependent manner, with an EC50 of 18.5 mM. Furthermore, this effect was observed in the presence of cytosolic free calcium (approximately 1 microM), but was absent in a cytosolic bath solution containing nominally zero free calcium (e.g.. 5 mM EGTA only), a condition under which these channels undergo largely voltage-dependent gating. Recordings of single BKCa channel events indicated that NH4+ increased the channel open probability of single channel activity approximately 3-fold, but did not alter the amplitude of single channel currents. These findings suggest that the calcium-sensitive gating of mammalian BKCa channels may be modified by other ions present in cytosolic solution.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Calgary, AB, Canada. abraun@ucalgary.ca
authors.forename: A P
authors.initials: AP
authors.lastname: Braun
mesh_terms: D000643:Ammonium Chloride / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000166:cytology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002414:Cations, Monovalent / Q000378:metabolism; D002478:Cells, Cultured; D004553:Electric Conductivity; D015640:Ion Channel Gating / Q000502:physiology*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials; D051379:Mice; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism / Q000502:physiology*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D002414:Cations, Monovalent; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D000644:Quaternary Ammonium Compounds; D000643:Ammonium Chloride; D002118:Calcium