title: Deglycosylation of the beta1-subunit of the BK channel changes its biophysical properties.
abstract: Large-conductance Ca(2+)-activated potassium (BK) channels are composed of pore-forming alpha-subunits and auxiliary beta-subunits. The alpha-subunits are widely expressed in many cell types, whereas the beta-subunits are more tissue specific and influence diverse aspects of channel function. In the current study, we identified the presence of the smooth muscle-specific beta1-subunit in murine colonic tissue using Western blotting. The native beta1-subunits migrated in SDS-PAGE as two molecular mass bands. Enzymatic removal of N-linked glycosylations from the beta1-subunit resulted in a single band that migrated at a lower molecular mass than the native beta1-subunit bands, suggesting that the native beta1-subunit exists in either a core glycosylated or highly glycosylated form. We investigated the functional consequence of deglycosylating the beta1-subunit during inside-out single-channel recordings. During inside-out single-channel recordings, with N-glycosidase F in the pipette solution, the open probability (P(o)) and mean open time of BK channels increased in a time-dependent manner. Deglycosylation of BK channels did not affect the conductance but shifted the steady-state voltage of activation toward more positive potentials without affecting slope when Ca(2+) concentration was <1 microM. Treatment of myocytes lacking the beta1-subunits of the BK channel with N-glycosidase F had no effect. These data suggest that glycosylations on the beta1-subunit in smooth muscle cells can modify the biophysical properties of BK channels.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557-0046, USA.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hagen
authors.forename: Kenton M
authors.initials: KM
authors.lastname: Sanders
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002413:Cations, Divalent / Q000494:pharmacology; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D004553:Electric Conductivity; D006031:Glycosylation / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000172:deficiency / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000494:pharmacology; D020033:Protein Isoforms / Q000172:deficiency / Q000187:drug effects / Q000378:metabolism / Q000502:physiology
chemical_list: D002413:Cations, Divalent; D051036:Large-Conductance Calcium-Activated Potassium Channels; D020033:Protein Isoforms; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase