A 59 amino acid insertion increases Ca2+ sensitivity of rbslo1, a Ca2+-activated K+ channel in renal epithelia

K. Hanaoka, J. M. Wright, I. B. Cheglakov, T. Morita, W. B. Guggino

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


We previously cloned a MaxiK channel α-subunit isoform, rbslo1, from rabbit kidney with an amino acid sequence highly homologous to mslo but with a 59 amino acid insertion between S8 and S9 (Morita et al., 1997. Am. J. Physiol. 273:F615-F624). rbslo1 activation properties differed substantially from mslo with much greater Ca2+ sensitivity, half-activation potential of -49 mV in 1 μM Ca2+. We now report single-channel analysis of rbslo1 and delA, a construct produced by removal of the 59 amino acid insertion at site A. delA is identical to mslo from upstream of S1 to downstream of S10 with the exception of 8 amino acids. Slope of the steady-state Boltzmann voltage activation curve was 8.1 mV per e-fold change in probability of opening for both rbslo1 and delA. The apparent [Ca2+](i) properties in delA were more like mslo but the voltage-activation properties remained distinctly rbslo1. Ca2+ affinity decreased and transmembrane voltage effects on apparent Ca2+ affinity increased in delA. The differences between rbslo1 and other cloned channels appear to be localized at insertion site A with both the insertion sequence and amino acid substitutions near site A being important. The steeper activation slope makes the channel more responsive to small changes in transmembrane voltage while the insertion sequence makes the channel functional at physiological low levels of [Ca2+](i).

Original languageEnglish (US)
Pages (from-to)193-201
Number of pages9
JournalJournal of Membrane Biology
Issue number3
StatePublished - 1999


  • BK channel
  • Gating
  • Potassium channel
  • Single-channel recording

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology


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