BK channel

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KCNMA1
File:BK-cartoon wp.jpg
The domain structure of BK channels
Identifiers
Symbol KCNMA1
Alt. symbols SLO
Entrez 3778
HUGO 6284
OMIM 600150
RefSeq NM_002247
UniProt Q12791
Other data
Locus Chr. 10 q22
KCNMB1
Identifiers
Symbol KCNMB1
Entrez 3779
HUGO 6285
OMIM 603951
RefSeq NM_004137
UniProt Q16558
Other data
Locus Chr. 5 q34
KCNMB2
Identifiers
Symbol KCNMB2
Entrez 10242
HUGO 6286
OMIM 605214
RefSeq NM_181361
UniProt Q9Y691
Other data
Locus Chr. 3 q26.32
KCNMB3
Identifiers
Symbol KCNMB3
Alt. symbols KCNMB2, KCNMBL
Entrez 27094
HUGO 6287
OMIM 605222
RefSeq NM_171828
UniProt Q9NPA1
Other data
Locus Chr. 3 q26.3-q27
KCNMB3L
Identifiers
Symbol KCNMB3L
Alt. symbols KCNMB2L, KCNMBLP
Entrez 27093
HUGO 6288
RefSeq NG_002679
Other data
Locus Chr. 22 q11.1
KCNMB4
Identifiers
Symbol KCNMB4
Entrez 27345
HUGO 6289
OMIM 605223
RefSeq NM_014505
UniProt Q86W47
Other data
Locus Chr. 12 q15
Calcium-activated BK potassium channel alpha subunit
Identifiers
Symbol BK_channel_a
Pfam PF03493
InterPro IPR003929

BK channels (Big Potassium), also called Maxi-K or slo1, are potassium channels characterized by their large conductance for potassium ions (K+) through cell membranes. These channels are activated (opened) by changes in membrane electrical potential and/or by increases in concentration of intracellular calcium ion (Ca2+).[1][2] Opening of BK channels allows K+ to passively flow through the channel, down the electrochemical gradient. Under typical physiological conditions, this results in an efflux of K+ from the cell, which leads to cell membrane hyperpolarization (an increase in the electrical potential across the cell membrane) and a decrease in cell excitability (a decrease in the probability that the cell will transmit an action potential).[3]

BK channels are essential for the regulation of several key physiological processes including smooth muscle tone and neuronal excitability.[4] They control the contraction of smooth muscle and are involved with the electrical tuning of hair cells in the cochlea. BK channels also contribute to the behavioral effects of ethanol in the worm C. elegans under high exogenous doses (> 100 mM) [5] that have been shown to correspond to biologically relevant internal ethanol concentrations.[6] It remains to be determined if BK channels contribute to intoxication in humans.

Structure

As with most other voltage-gated potassium channels, BK channels have a tetrameric structure. Each monomer of the channel-forming alpha subunit is the product of the KCNMA1 gene. Modulatory beta subunits (encoded by KCNMB1, KCNMB2, KCNMB3, or KCNMB4) can associate with the tetrametic channel.

BK channels are a prime example of modular protein evolution. Each BK channel alpha subunit consists of (from N- to C-terminal):

  1. A unique transmembrane domain (S0)[7] that precedes the 6 transmembrane domains (S1-S6) conserved in all voltage-dependent K+ channels.
  2. A voltage sensing domain (S1-S4).
  3. A K+ channel pore domain (S5, selectivity filter, and S6).
  4. A cytoplasmic C-terminal domain (CTD) consisting of a pair of RCK (Regulator of Conductance of K+) domains that assemble into an octameric gating ring on the intracellular side of the tetrameric channel.[8][9][10][11][12] The CTD contains four primary binding sites for Ca2+, called "calcium bowls", encoded within the second RCK domain of each monomer.[2][8][12][13]

Available X-ray structures:

  • 3MT5 - Crystal Structure of the Human BK Gating Apparatus[2]
  • 3NAF - Structure of the Intracellular Gating Ring from the Human High-conductance Ca2+ gated K+ Channel (BK Channel)[8]
  • 3U6N - Open Structure of the BK channel Gating Ring[13]

Pharmacology

BK channels are pharmacological targets for the treatment of several medical disorders including stroke[14] and overactive bladder.[15] Although pharmaceutical companies have attempted to develop synthetic molecules targeting BK channels,[16] their efforts have proved largely ineffective. For instance, BMS-204352, a molecule developed by Bristol-Myers Squibb, failed to improve clinical outcome in stroke patients compared to placebo.[17] However, BKCa channels are reduced in patients suffering from the Fragile X syndrome[18] and the agonist, BMS-204352, corrects some of the deficits observed in Fmr1 knockout mice, a model of Fragile X syndrome.[19]

BK channels have also been found to be activated by exogenous pollutants and endogenous gasotransmitters carbon monoxide[20][21] and hydrogen sulphide.[22]

BK channels can be readily inhibited by a range of compounds including tetraethylammonium (TEA), paxilline[23] and iberiotoxin.[24]

The BKCa-channel blocker GAL-021 has been investigated for potential use in inhibiting opioid induced respiratory depression without affecting analgesia.[25]

See also

References

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ EntrezGene 3778
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 8.2 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ 12.0 12.1 Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ 13.0 13.1 Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  25. ↑ McLeod JF, Leempoels JM, Peng SX, Dax SL, Myers LJ, Golder FJ. GAL-021, a new intravenous BKCa-channel blocker, is well tolerated and stimulates ventilation in healthy volunteers. Br J Anaesth. 2014 Nov;113(5):875-83. doi: 10.1093/bja/aeu182 PMID 24989775

External links

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