Abstract.
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 .
Similar content being viewed by others
Author information
Authors and Affiliations
Additional information
Received: 23 August 1999
Rights and permissions
About this article
Cite this article
Hanaoka, K., Wright, J., Cheglakov, I. et al. A 59 Amino Acid Insertion Increases Ca2+ Sensitivity of rbslo1, a Ca2+-Activated K+ Channel in Renal Epithelia. J. Membrane Biol. 172, 193–201 (1999). https://doi.org/10.1007/s002329900596
Issue Date:
DOI: https://doi.org/10.1007/s002329900596