Abstract
BK channels are activated by intracellular Ca 2+ and Mg 2+ as well as by depolarization. Such activation is possible because each of the four subunits has two high-affinity Ca 2+ sites, one low-affinity Mg 2+ site, and a voltage sensor. This study further investigates the mechanism of Mg 2+ activation by using single-channel recording to determine separately the action of Mg 2+ on the open and closed states of the channel. To limit Mg 2+ action to the Mg 2+ sites, the two high-affinity Ca 2+ sites are disabled by mutation. When the voltage is stepped from negative holding potentials to +100 mV, we find that 10 mM Mg 2+ decreases the mean closed latency to the first channel opening 2.1-fold, decreases the mean closed interval duration 8.7-fold, increases mean burst duration 10.1-fold, increases the number of openings per burst 4.4-fold, and increases mean open interval duration 2.3-fold. Hence, Mg 2+ can bind to closed BK channels, increasing their opening rates, and to open BK channels, decreasing their closing rates. To explore the relationship between Mg 2+ action and voltage sensor activation, we record single-channel activity in macropatches containing hundreds of channels. Open probability (P o) is dramatically increased by 10 mM Mg 2+ when voltage sensors are activated with either depolarization or the mutation R210C. The increased P o arises from large decreases in mean closed interval durations and moderate increases in mean open interval durations. In contrast, 10 mM Mg 2+ has no detectable effects on P o or interval durations when voltage sensors are deactivated with very negative potentials or the mutation R167E. These observations are consistent with a model in which Mg 2+ can bind to and alter the gating of both closed and open states to increase P o, provided that one or more voltage sensors are activated.
| Original language | English |
|---|---|
| Pages (from-to) | 593-607 |
| Number of pages | 15 |
| Journal | Journal of General Physiology |
| Volume | 138 |
| Issue number | 6 |
| DOIs | |
| State | Published - Dec 1 2011 |
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ASJC Scopus subject areas
- Physiology
Cite this
Mg 2+ binding to open and closed states can activate BK channels provided that the voltage sensors are elevated. / Chen, Ren Shiang; Geng, Yanyan; Magleby, Karl.
In: Journal of General Physiology, Vol. 138, No. 6, 01.12.2011, p. 593-607.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Mg 2+ binding to open and closed states can activate BK channels provided that the voltage sensors are elevated
AU - Chen, Ren Shiang
AU - Geng, Yanyan
AU - Magleby, Karl
PY - 2011/12/1
Y1 - 2011/12/1
N2 - BK channels are activated by intracellular Ca 2+ and Mg 2+ as well as by depolarization. Such activation is possible because each of the four subunits has two high-affinity Ca 2+ sites, one low-affinity Mg 2+ site, and a voltage sensor. This study further investigates the mechanism of Mg 2+ activation by using single-channel recording to determine separately the action of Mg 2+ on the open and closed states of the channel. To limit Mg 2+ action to the Mg 2+ sites, the two high-affinity Ca 2+ sites are disabled by mutation. When the voltage is stepped from negative holding potentials to +100 mV, we find that 10 mM Mg 2+ decreases the mean closed latency to the first channel opening 2.1-fold, decreases the mean closed interval duration 8.7-fold, increases mean burst duration 10.1-fold, increases the number of openings per burst 4.4-fold, and increases mean open interval duration 2.3-fold. Hence, Mg 2+ can bind to closed BK channels, increasing their opening rates, and to open BK channels, decreasing their closing rates. To explore the relationship between Mg 2+ action and voltage sensor activation, we record single-channel activity in macropatches containing hundreds of channels. Open probability (P o) is dramatically increased by 10 mM Mg 2+ when voltage sensors are activated with either depolarization or the mutation R210C. The increased P o arises from large decreases in mean closed interval durations and moderate increases in mean open interval durations. In contrast, 10 mM Mg 2+ has no detectable effects on P o or interval durations when voltage sensors are deactivated with very negative potentials or the mutation R167E. These observations are consistent with a model in which Mg 2+ can bind to and alter the gating of both closed and open states to increase P o, provided that one or more voltage sensors are activated.
AB - BK channels are activated by intracellular Ca 2+ and Mg 2+ as well as by depolarization. Such activation is possible because each of the four subunits has two high-affinity Ca 2+ sites, one low-affinity Mg 2+ site, and a voltage sensor. This study further investigates the mechanism of Mg 2+ activation by using single-channel recording to determine separately the action of Mg 2+ on the open and closed states of the channel. To limit Mg 2+ action to the Mg 2+ sites, the two high-affinity Ca 2+ sites are disabled by mutation. When the voltage is stepped from negative holding potentials to +100 mV, we find that 10 mM Mg 2+ decreases the mean closed latency to the first channel opening 2.1-fold, decreases the mean closed interval duration 8.7-fold, increases mean burst duration 10.1-fold, increases the number of openings per burst 4.4-fold, and increases mean open interval duration 2.3-fold. Hence, Mg 2+ can bind to closed BK channels, increasing their opening rates, and to open BK channels, decreasing their closing rates. To explore the relationship between Mg 2+ action and voltage sensor activation, we record single-channel activity in macropatches containing hundreds of channels. Open probability (P o) is dramatically increased by 10 mM Mg 2+ when voltage sensors are activated with either depolarization or the mutation R210C. The increased P o arises from large decreases in mean closed interval durations and moderate increases in mean open interval durations. In contrast, 10 mM Mg 2+ has no detectable effects on P o or interval durations when voltage sensors are deactivated with very negative potentials or the mutation R167E. These observations are consistent with a model in which Mg 2+ can bind to and alter the gating of both closed and open states to increase P o, provided that one or more voltage sensors are activated.
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U2 - 10.1085/jgp.201110707
DO - 10.1085/jgp.201110707
M3 - Article
VL - 138
SP - 593
EP - 607
JO - Journal of General Physiology
JF - Journal of General Physiology
SN - 0022-1295
IS - 6
ER -