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Paxilline inhibits BK channels by an almost exclusively closed-channel block mechanism.

Zhou Y, Lingle CJ - J. Gen. Physiol. (2014)

Bottom Line: Measurements of Po times the number of channels at negative potentials support the idea that paxilline increases occupancy of closed states, effectively reducing the closed-open equilibrium constant, L(0).However, paxilline does not hinder MTSET modification of the inner cavity residue, A313C.We conclude that paxilline binds more tightly to the closed conformation, favoring occupancy of closed-channel conformations, and propose that it binds to a superficial position near the entrance to the central cavity, but does not hinder access of smaller molecules to this cavity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110.

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Essentially complete recovery from paxilline block can occur, even in the continuous presence of paxilline under conditions of high Po. (A) The indicated test-pulse sequence was applied every 1 s while holding at −80 mV with 300 µM Ca2+. The traces show before paxilline application, after ∼50% inhibition by paxilline, and during the full paxilline effect. (B) For the same patch in A, the equilibration conditions were altered to 80 mV with 300 µM Ca2+ while still in the continuous presence of 100 nM paxilline. Brief sojourns to −80 mV with test steps to 160 mV were used to monitor recovery in the presence of paxilline. A 60-s washout of paxilline confirmed that no additional recovery occurred. (C) The time course of onset and recovery from inhibition by 100 nM paxilline, while in the continuous presence of paxilline, is plotted for the cell shown in A and B, with the numbers corresponding to the approximate times of the traces in A and B.
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fig4: Essentially complete recovery from paxilline block can occur, even in the continuous presence of paxilline under conditions of high Po. (A) The indicated test-pulse sequence was applied every 1 s while holding at −80 mV with 300 µM Ca2+. The traces show before paxilline application, after ∼50% inhibition by paxilline, and during the full paxilline effect. (B) For the same patch in A, the equilibration conditions were altered to 80 mV with 300 µM Ca2+ while still in the continuous presence of 100 nM paxilline. Brief sojourns to −80 mV with test steps to 160 mV were used to monitor recovery in the presence of paxilline. A 60-s washout of paxilline confirmed that no additional recovery occurred. (C) The time course of onset and recovery from inhibition by 100 nM paxilline, while in the continuous presence of paxilline, is plotted for the cell shown in A and B, with the numbers corresponding to the approximate times of the traces in A and B.

Mentions: The ability of inhibition by paxilline to be reversed by changes in equilibration conditions, even in the constant presence of paxilline, was also confirmed in patches with large numbers of BK channels (Fig. 4). Specifically, after onset of block in 100 nM paxilline (Fig. 4 A), changing the equilibration conditions to those favoring unblocking can produce recovery from paxilline inhibition (Fig. 4, B and C). It may be noticed that the onset of paxilline inhibition appears variable during wash-in of paxilline. This is addressed below and appears to reflect variability in paxilline access to the patch, despite the rapidity of solution exchange with small charged molecules.


Paxilline inhibits BK channels by an almost exclusively closed-channel block mechanism.

Zhou Y, Lingle CJ - J. Gen. Physiol. (2014)

Essentially complete recovery from paxilline block can occur, even in the continuous presence of paxilline under conditions of high Po. (A) The indicated test-pulse sequence was applied every 1 s while holding at −80 mV with 300 µM Ca2+. The traces show before paxilline application, after ∼50% inhibition by paxilline, and during the full paxilline effect. (B) For the same patch in A, the equilibration conditions were altered to 80 mV with 300 µM Ca2+ while still in the continuous presence of 100 nM paxilline. Brief sojourns to −80 mV with test steps to 160 mV were used to monitor recovery in the presence of paxilline. A 60-s washout of paxilline confirmed that no additional recovery occurred. (C) The time course of onset and recovery from inhibition by 100 nM paxilline, while in the continuous presence of paxilline, is plotted for the cell shown in A and B, with the numbers corresponding to the approximate times of the traces in A and B.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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fig4: Essentially complete recovery from paxilline block can occur, even in the continuous presence of paxilline under conditions of high Po. (A) The indicated test-pulse sequence was applied every 1 s while holding at −80 mV with 300 µM Ca2+. The traces show before paxilline application, after ∼50% inhibition by paxilline, and during the full paxilline effect. (B) For the same patch in A, the equilibration conditions were altered to 80 mV with 300 µM Ca2+ while still in the continuous presence of 100 nM paxilline. Brief sojourns to −80 mV with test steps to 160 mV were used to monitor recovery in the presence of paxilline. A 60-s washout of paxilline confirmed that no additional recovery occurred. (C) The time course of onset and recovery from inhibition by 100 nM paxilline, while in the continuous presence of paxilline, is plotted for the cell shown in A and B, with the numbers corresponding to the approximate times of the traces in A and B.
Mentions: The ability of inhibition by paxilline to be reversed by changes in equilibration conditions, even in the constant presence of paxilline, was also confirmed in patches with large numbers of BK channels (Fig. 4). Specifically, after onset of block in 100 nM paxilline (Fig. 4 A), changing the equilibration conditions to those favoring unblocking can produce recovery from paxilline inhibition (Fig. 4, B and C). It may be noticed that the onset of paxilline inhibition appears variable during wash-in of paxilline. This is addressed below and appears to reflect variability in paxilline access to the patch, despite the rapidity of solution exchange with small charged molecules.

Bottom Line: Measurements of Po times the number of channels at negative potentials support the idea that paxilline increases occupancy of closed states, effectively reducing the closed-open equilibrium constant, L(0).However, paxilline does not hinder MTSET modification of the inner cavity residue, A313C.We conclude that paxilline binds more tightly to the closed conformation, favoring occupancy of closed-channel conformations, and propose that it binds to a superficial position near the entrance to the central cavity, but does not hinder access of smaller molecules to this cavity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110.

Show MeSH