| 1. |
- Birnir, Bryndis, et al.
(författare)
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Bicuculline, pentobarbital and diazepam modulate spontaneous GABA(A) channels in rat hippocampal neurons
- 2000
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Ingår i: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 131:4, s. 695-704
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneously opening, chloride-selective channels that showed outward rectification were recorded in ripped-off patches from rat cultured hippocampal neurons and in cell-attached patches from rat hippocampal CA1 pyramidal neurons in slices. In both preparations, channels had multiple conductance states and the most common single-channel conductance varied. In the outside-out patches it ranged from 12 to 70 pS (Vp=40 mV) whereas in the cell-attached patches it ranged from 56 to 85 pS (-Vp=80 mV). Application of GABA to a patch showing spontaneous channel activity evoked a rapid, synchronous activation of channels. During prolonged exposure to either 5 or 100 microM GABA, the open probability of channels decreased. Application of GABA appeared to have no immediate effect on single-channel conductance. Exposure of the patches to 100 microM bicuculline caused a gradual decrease on the single-channel conductance of the spontaneous channels. The time for complete inhibition to take place was slower in the outside-out than in the cell-attached patches. Application of 100 microM pentobarbital or 1 microM diazepam caused 2 - 4 fold increase in the maximum channel conductance of low conductance (<40 pS) spontaneously active channels. The observation of spontaneously opening GABA(A) channels in cell-attached patches on neurons in slices suggests that they may have a role in neurons in vivo and could be an important site of action for some drugs such as benzodiazepines, barbiturates and general anaesthetics.
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| 2. |
- Birnir, Bryndis, et al.
(författare)
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GABA concentration sets the conductance of delayed GABAA channels in outside-out patches from rat hippocampal neurons.
- 2001
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 181:3, s. 171-83
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Tidskriftsartikel (refereegranskat)abstract
- GABAA channels were activated by GABA in outside-out patches from rat cultured hippocampal neurons. They were blocked by bicuculline and potentiated by diazepam. In 109 of 190 outside-out patches, no channels were active before exposure to GABA (silent patches). The other 81 patches showed spontaneous channel activity. In patches containing spontaneous channel activity, rapid application of GABA rapidly activated channels. In 93 of the silent patches, channels could be activated by GABA but only after a delay that was sometimes as long as 10 minutes. The maximum channel conductance of the channels activated after a delay increased with GABA concentration from less than 10 pS (0.5 microm GABA) to more than 100 pS (10 mm GABA). Fitting the data with a Hill-type equation gave an EC50 value of 33 microm and a Hill coefficient of 0.6. The channels showed outward rectification and were chloride selective. In the presence of 1 microm diazepam, the GABA EC50 decreased to 0.2 microm but the maximum conductance was unchanged. Diazepam decreased the average latency for channel opening. Bicuculline, a GABA antagonist, caused a concentration-dependent decrease in channel conductance. In channels activated with 100 microm GABA the bicuculline IC50 was 19 microm. The effect of GABA on channel conductance shows that the role of the ligand in GABAA receptor channel function is more complex than previously thought.
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| 3. |
- Eghbali, M, et al.
(författare)
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Effects of propofol on GABA(A) channel conductance in rat-cultured hippocampal neurons
- 2003
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Ingår i: European Journal of Pharmacology. - 1879-0712. ; 468:2, s. 75-82
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Tidskriftsartikel (refereegranskat)abstract
- Channels were activated, in ripped-off patches from rat-cultured hippocampal neurons, by propofol alone, propofol plus 0.5 muM GABA (gamma-aminobutyric acid) or GABA alone. The propofol-activated currents were chloride-selective, showed outward-rectification and were enhanced by 1 muM diazepam. The maximum propofol-activated channel conductance increased with propofol concentration from less than 15 pS (10 muM) to about 60 pS (500 muM) but decreased to 40 pS in 1 mM propofol. Fitting the data from 10 to 500 muM propofol with a Hill-type equation gave a maximum conductance of 64 pS, an EC50 value of 32 muM and a Hill coefficient of 1.1. Addition of 0.5 muM GABA shifted the propofol EC50 value to 10 muM and increased the maximum channel conductance to about 100 pS. The Hill coefficient was 0.8. The maximum channel conductance did not increase further when 1 muM diazepam was added together with a saturating propofol concentration and GABA. The results are compared to effects other drugs have on GABA(A) channels conductance. (C) 2003 Elsevier Science B.V All rights reserved.
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| 4. |
- Eghbali, M, et al.
(författare)
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Hippocampal GABA(A) channel conductance increased by diazepam
- 1997
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 388:6637, s. 71-75
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Tidskriftsartikel (refereegranskat)abstract
- Benzodiazepines, which are widely used clinically for relief of anxiety and for sedation, are thought to enhance synaptic inhibition in the central nervous system by increasing the open probability of chloride channels activated by the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Here we show that the benzodiazepine diazepam can also increase the conductance of GABAA channels activated by low concentrations of GABA (0.5 or 5 microM) in rat cultured hippocampal neurons. Before exposure to diazepam, chloride channels activated by GABA had conductances of 8 to 53pS. Diazepam caused a concentration-dependent and reversible increase in the conductance of these channels towards a maximum conductance of 70-80 pS and the effect was as great as 7-fold in channels of lowest initial conductance. Increasing the conductance of GABAA channels tonically activated by low ambient concentrations of GABA in the extracellular environment may be an important way in which these drugs depress excitation in the central nervous system. That any drug has such a large effect on single channel conductance has not been reported previously and has implications for models of channel structure and conductance.
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| 5. |
- Eghbali, M, et al.
(författare)
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Pentobarbital modulates gamma-aminobutyric acid-activated single-channel conductance in rat cultured hippocampal neurons.
- 2000
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Ingår i: Molecular Pharmacology. - 0026-895X .- 1521-0111. ; 58:3, s. 463-9
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Tidskriftsartikel (refereegranskat)abstract
- We examined the effect of a range of pentobarbital concentrations on 0.5 microM gamma-aminobutyric acid (GABA)-activated channels (10 +/- 1 pS) in inside-out or outside-out patches from rat cultured hippocampal neurons. The conductance increased from 12 +/- 4 to 62 +/- 9 pS as the pentobarbital concentration was raised from 10 to 500 microM and the data could be fitted by a Hill-type equation. At 100 microM pentobarbital plus 0.5 microM GABA, the conductance seemed to reach a plateau. The pentobarbital EC(50)(0.5 microM GABA) value was 22 +/- 4 microM and n was 1.9 +/- 0.5. In 1 mM pentobarbital plus 0.5 microM GABA, the single-channel conductance decreased to 34 +/- 8 pS. This apparent inhibition of channel conductance was relieved by 1 microM diazepam. The channel conductance was 64 +/- 6 pS in the presence of all three drugs. The channels were open more in the presence of both GABA and pentobarbital than in the presence of either drug alone. Pentobarbital alone (100 microM) activated channels with conductance (30 +/- 2 pS) and kinetic properties distinct from those activated by either GABA alone or GABA plus pentobarbital. Whether pentobarbital induces new conformations or promotes conformations observed in the presence of GABA alone cannot be determined from our study, but the results clearly show that it is the combination of drugs present that determines the single-channel conductance and the kinetic properties of the receptors.
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| 6. |
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| 7. |
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| 8. |
- Yu, Tiangxiong, et al.
(författare)
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A-MYB/TCFL5 regulatory architecture ensures the production of pachytene piRNAs in placental mammals
- 2023
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Ingår i: RNA. - : Cold Spring Harbor Laboratory. - 1355-8382 .- 1469-9001. ; 29:1, s. 30-43
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Tidskriftsartikel (refereegranskat)abstract
- In male mice, the transcription factor A-MYB initiates the transcription of pachytene piRNA genes during meiosis. Here, we report that A-MYB activates the transcription factor Tcfl5 produced in pachytene spermatocytes. Subsequently, A-MYB and TCFL5 reciprocally reinforce their own transcription to establish a positive feedback circuit that triggers pachytene piRNA production. TCFL5 regulates the expression of genes required for piRNA maturation and promotes transcription of evolutionarily young pachytene piRNA genes, whereas A-MYB activates the transcription of older pachytene piRNA genes. Intriguingly, pachytene piRNAs from TCFL5-dependent young loci initiate the production of piRNAs from A-MYB-dependent older loci, ensuring the self-propagation of pachytene piRNAs. A-MYB and TCFL5 act via a set of incoherent feedforward loops that drive regulation of gene expression by pachytene piRNAs during spermatogenesis. This regulatory architecture is conserved in rhesus macaque, suggesting that it was present in the last common ancestor of placental mammals.
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