title: Gating of recombinant small-conductance Ca-activated K+ channels by calcium.
abstract: Small-conductance Ca-activated K+ channels play an important role in modulating excitability in many cell types. These channels are activated by submicromolar concentrations of intracellular Ca2+, but little is known about the gating kinetics upon activation by Ca2+. In this study, single channel currents were recorded from Xenopus oocytes expressing the apamin-sensitive clone rSK2. Channel activity was detectable in 0.2 micro M Ca2+ and was maximal above 2 micro M Ca2+. Analysis of stationary currents revealed two open times and three closed times, with only the longest closed time being Ca dependent, decreasing with increasing Ca2+ concentrations. In addition, elevated Ca2+ concentrations resulted in a larger percentage of long openings and short closures. Membrane voltage did not have significant effects on either open or closed times. The open probability was approximately 0.6 in 1 micro M free Ca2+. A lower open probability of approximately 0.05 in 1 micro M Ca2+ was also observed, and channels switched spontaneously between behaviors. The occurrence of these switches and the amount of time channels spent displaying high open probability behavior was Ca2+ dependent. The two behaviors shared many features including the open times and the short and intermediate closed times, but the low open probability behavior was characterized by a different, long Ca2+-dependent closed time in the range of hundreds of milliseconds to seconds. Small-conductance Ca- activated K+ channel gating was modeled by a gating scheme consisting of four closed and two open states. This model yielded a close representation of the single channel data and predicted a macroscopic activation time course similar to that observed upon fast application of Ca2+ to excised inside-out patches.
authors.affiliation: Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201, USA.
authors.forename: B
authors.initials: B
authors.lastname: Hirschberg
authors.forename: J
authors.initials: J
authors.lastname: Maylie
authors.forename: J P
authors.initials: JP
authors.lastname: Adelman
authors.forename: N V
authors.initials: NV
authors.lastname: Marrion
mesh_terms: D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D007425:Intracellular Membranes / Q000378:metabolism; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D008954:Models, Biological; D009865:Oocytes; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated; D051381:Rats; D011994:Recombinant Proteins; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013997:Time Factors; D014981:Xenopus
chemical_list: C496899:Kcnn2 protein, rat; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011994:Recombinant Proteins; D051640:Small-Conductance Calcium-Activated Potassium Channels; D001030:Apamin; D002118:Calcium