Elimination of the BK(Ca) channel's high-affinity Ca(2+) sensitivity.
We report here a combination of site-directed mutations that eliminate the high-affinity Ca(2+) response of the large-conductance Ca(2+)-activated K(+) channel (BK(Ca)), leaving only a low-affinity response blocked by high concentrations of Mg(2+). Mutations at two sites are required, the "Ca(2+) bowl," which has been implicated previously in Ca(2+) binding, and M513, at the end of the channel's seventh hydrophobic segment. Energetic analyses of mutations at these positions, alone and in combination, argue that the BK(Ca) channel contains three types of Ca(2+) binding sites, one of low affinity that is Mg(2+) sensitive (as has been suggested previously) and two of higher affinity that have similar binding characteristics and contribute approximately equally to the power of Ca(2+) to influence channel opening. Estimates of the binding characteristics of the BK(Ca) channel's high-affinity Ca(2+)-binding sites are provided.
Bao
Lin
L
Molecular Cardiology Research Institute, New England Medical Center, and the Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA.
Rapin
Anne M
AM
Holmstrand
Ericka C
EC
Cox
Daniel H
DH
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D009154:Mutation / Q000502:physiology; D009865:Oocytes; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D008274:Magnesium; D002118:Calcium