| 1. |
- Nilsson, Johanna, et al.
(författare)
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Bupivacaine Blocks N-Type Inactivating K-v Channels in the Open State : No Allosteric Effect on Inactivation Kinetics
- 2008
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 95:11, s. 5138-5152
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Tidskriftsartikel (refereegranskat)abstract
- Local anesthetics bind to ion channels in a state-dependent manner. For noninactivating voltage-gated K channels the binding mainly occurs in the open state, while for voltage-gated inactivating Na channels it is assumed to occur mainly in inactivated states, leading to an allosterically caused increase in the inactivation probability, reflected in a negative shift of the steady-state inactivation curve, prolonged recovery from inactivation, and a frequency-dependent block. How local anesthetics bind to N-type inactivating K channels is less explored. In this study, we have compared bupivacaine effects on inactivating (Shaker and K(v)3.4) and noninactivating (Shaker-IR and K(v)3.2) channels, expressed in Xenopus oocytes. Bupivacaine was found to block these channels time-dependently without shifting the steady-state inactivation curve markedly, without a prolonged recovery from inactivation, and without a frequency-dependent block. An analysis, including computational testing of kinetic models, suggests binding to the channel mainly in the open state, with affinities close to those estimated for corresponding noninactivating channels (300 and 280 mu M for Shaker and Shaker-IR, and 60 and 90 mu M for K(v)3.4 and K(v)3.2). The similar magnitudes of K-d, as well as of blocking and unblocking rate constants for inactivating and noninactivating Shaker channels, most likely exclude allosteric interactions between the inactivation mechanism and the binding site. The relevance of these results for understanding the action of local anesthetics on Na channels is discussed.
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| 2. |
- Ågren, Richard, et al.
(författare)
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Ligand with Two Modes of Interaction with the Dopamine D-2 Receptor-An Induced-Fit Mechanism of Insurmountable Antagonism
- 2020
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Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 11:19, s. 3130-3143
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Tidskriftsartikel (refereegranskat)abstract
- A solid understanding of the mechanisms governing ligand binding is crucial for rational design of therapeutics targeting the dopamine D2 receptor (D2R). Here, we use G protein-coupled inward rectifier potassium (GIRK) channel activation in Xenopus oocytes to measure the kinetics of D2R antagonism by a series of aripiprazole analogues, as well as the recovery of dopamine (DA) responsivity upon washout. The aripiprazole analogues comprise an orthosteric and a secondary pharmacophore and differ by the length of the saturated carbon linker joining these two pharmacophores. Two compounds containing 3- and 5-carbon linkers allowed for a similar extent of recovery from antagonism in the presence of 1 or 100 μM DA (>25 and >90% of control, respectively), whereas recovery was less prominent (∼20%) upon washout of the 4-carbon linker compound, SV-III-130, both with 1 and 100 μM DA. Prolonging the coincubation time with SV-III-130 further diminished recovery. Curve-shift experiments were consistent with competition between SV-III-130 and DA. Two mutations in the secondary binding pocket (V91A and E95A) of D2R decreased antagonistic potency and increased recovery from SV-III-130 antagonism, whereas a third mutation (L94A) only increased recovery. Our results suggest that the secondary binding pocket influences recovery from inhibition by the studied aripiprazole analogues. We propose a mechanism, supported by in silico modeling, whereby SV-III-130 initially binds reversibly to the D2R, after which the drug-receptor complex undergoes a slow transition to a second ligand-bound state, which is dependent on secondary binding pocket integrity and irreversible during the time frame of our experiments.
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