Gating of recombinant small-conductance Ca-activated K+ channels by calcium

Birgit Hirschberg, James Maylie, John P. Adelman, Neil V. Marrion

Research output: Contribution to journalArticle

139 Scopus citations

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 grating 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 μM Ca2+ and was maximal above 2 μM 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 ~0.6 in 1 μM free Ca2+. A lower open probability of ~0.05 in 1 μM 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 grating 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.

Original languageEnglish (US)
Pages (from-to)565-581
Number of pages17
JournalJournal of General Physiology
Volume111
Issue number4
DOIs
StatePublished - Apr 1 1998

Keywords

  • Afterhyperpolarization
  • Calcium-activated
  • Gating
  • Potassium channel
  • Single channel

ASJC Scopus subject areas

  • Physiology

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