title: Unique inner pore properties of BK channels revealed by quaternary ammonium block.
abstract: Potassium channels have a very wide distribution of single-channel conductance, with BK type Ca(2+)-activated K(+) channels having by far the largest. Even though crystallographic views of K(+) channel pores have become available, the structural basis underlying BK channels' large conductance has not been completely understood. In this study we use intracellularly applied quaternary ammonium compounds to probe the pore of BK channels. We show that molecules as large as decyltriethylammonium (C(10)) and tetrabutylammonium (TBA) have much faster block and unblock rates in BK channels when compared with any other tested K(+) channel types. Additionally, our results suggest that at repolarization large QA molecules may be trapped inside blocked BK channels without slowing the overall process of deactivation. Based on these findings we propose that BK channels may differ from other K(+) channels in its geometrical design at the inner mouth, with an enlarged cavity and inner pore providing less spatially restricted access to the cytoplasmic solution. These features could potentially contribute to the large conductance of BK channels.
authors.affiliation: Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA. raldrich@stanford.edu
authors.forename: Weiyan
authors.initials: W
authors.lastname: Li
authors.forename: Richard W
authors.initials: RW
authors.lastname: Aldrich
mesh_terms: D000818:Animals; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology*; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008956:Models, Chemical; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated / Q000737:chemistry / Q000502:physiology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D014982:Xenopus laevis
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D000644:Quaternary Ammonium Compounds; C013912:decyltrimethylammonium; C009405:tetrabutylammonium; D011188:Potassium