期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2003
卷号：100
期号：17
页码：10061-10066
DOI：10.1073/pnas.1731650100
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The {beta}1 subunit of BK (large conductance Ca2+ and voltage-activated K+) channels is essential for many key physiological processes, such as controlling the contraction of smooth muscle and the tuning of hair cells in the cochlea. Although it is known that the {beta}1 subunit greatly increases the open probability of BK channels, little is known about its mechanism of action. We now explore this mechanism by using channels in which the Ca2+- and Mg2+-dependent activating mechanisms have been disrupted by mutating three sites to remove the Ca2+ and Mg2+ sensitivity. We find that the presence of the {beta}1 subunit partially restores Ca2+ sensitivity to the triply mutated channels, but not the Mg2+ sensitivity. We also find that the {beta}1 subunit has no effect on the Mg2+ sensitivity of WT BK channels, in contrast to its pronounced effect of increasing the apparent Ca2+ sensitivity. These observations suggest that the {beta}1 subunit increases open probability by working through the Ca2+-dependent, rather than Mg2+-dependent, activating mechanisms, and that the action of the {beta}1 subunit is not directly on the Ca2+ binding sites, but on the allosteric machinery coupling the sites to the gate. The differential effects of the {beta}1 subunit on the Ca2+ and Mg2+ activation of the channel suggest that these processes act separately. Finally, we show that [IMG]f1.gif" ALT="Formula" BORDER="0"> inhibits, rather than activates, BK channels in the presence of the {beta}1 subunit for intermediate levels of [IMG]f2.gif" ALT="Formula" BORDER="0">. This Mg2+ inhibition in the presence of the {beta}1 subunit provides an additional regulatory mechanism of BK channel activity.
