Facilitation of recurrent inhibition in rat hippocampus by barbiturate and related nonbarbiturate depressant drugs

ABSTRACT The effects of anticonvulsant, anesthetic and convulsant barbiturates and of related depressant drugs were characterized on excitatory and inhibitory synaptic transmission in slices of rat hippocampus

Allosteric Control of Gating and Kinetics at P2X₄ Receptor Channels

The CNS abundantly expresses P2X receptor channels for ATP; of these the most widespread in the brain is the P2X₄ channel. We show that ivermectin (IVM) is a specific positive allosteric effector of heterologously expressed P2X₄ and possibly of heteromeric P2X₄/P2X₆channels, but not of P2X₂, P2X₃, P2X₂/P2X₃, or P2X₇ channels. In the submicromolar range (EC₅₀, ∼250 nM) the action of IVM was rapid and reversible, resulting in increased amplitude and slowed deactivation of P2X₄ channel currents evoked by ATP. IVM also markedly increased the potency of ATP and that of the normally low-potency agonist α,β-methylene-ATP in a use- and voltage-independent manner without changing the ion selectivity of P2X₄ channels. Therefore, IVM evokes a potent pharmacological gain-of-function phenotype that is specific for P2X₄ channels. We also tested whether IVM could modulate endogenously expressed P2X channels in the adult trigeminal mesencephalic nucleus and hippocampal CA1 neurons. Surprisingly, IVM produced no significant effect on the fast ATP-evoked inward currents in either type of neuron, despite the fact that IVM modulated P2X₄ channels heterologously expressed in embryonic hippocampal neurons. These results suggest that homomeric P2X₄ channels are not the primary subtype of P2X receptor in the adult trigeminal mesencephalic nucleus and in hippocampal CA1 neurons

Allosteric Control of Gating and Kinetics at P2X₄ Receptor Channels

The CNS abundantly expresses P2X receptor channels for ATP; of these the most widespread in the brain is the P2X₄ channel. We show that ivermectin (IVM) is a specific positive allosteric effector of heterologously expressed P2X₄ and possibly of heteromeric P2X₄/P2X₆channels, but not of P2X₂, P2X₃, P2X₂/P2X₃, or P2X₇ channels. In the submicromolar range (EC₅₀, ∼250 nM) the action of IVM was rapid and reversible, resulting in increased amplitude and slowed deactivation of P2X₄ channel currents evoked by ATP. IVM also markedly increased the potency of ATP and that of the normally low-potency agonist α,β-methylene-ATP in a use- and voltage-independent manner without changing the ion selectivity of P2X₄ channels. Therefore, IVM evokes a potent pharmacological gain-of-function phenotype that is specific for P2X₄ channels. We also tested whether IVM could modulate endogenously expressed P2X channels in the adult trigeminal mesencephalic nucleus and hippocampal CA1 neurons. Surprisingly, IVM produced no significant effect on the fast ATP-evoked inward currents in either type of neuron, despite the fact that IVM modulated P2X₄ channels heterologously expressed in embryonic hippocampal neurons. These results suggest that homomeric P2X₄ channels are not the primary subtype of P2X receptor in the adult trigeminal mesencephalic nucleus and in hippocampal CA1 neurons

Antagonists of the Receptor-G Protein Interface Block Gi-coupled Signal Transduction

The carboxyl terminus of heterotrimeric G protein alpha subunits plays an important role in receptor interaction. We demonstrate that peptides corresponding to the last 11 residues of Galphai1/2 or Galphao1 impair agonist binding to A1 adenosine receptors, whereas Galphas or Galphat peptides have no effect. Previously, by using a combinatorial library we identified a series of Galphat peptide analogs that bind rhodopsin with high affinity (Martin, E. L., Rens-Domiano, S., Schatz, P. J., and Hamm, H. E. (1996) J. Biol. Chem. 271, 361-366). Native Galphai1/2 peptide as well as several analogs were tested for their ability to modulate agonist binding or antagonist-agonist competition using cells overexpressing human A1 adenosine receptors. Three peptide analogs decreased the Ki, suggesting that they disrupt the high affinity receptor-G protein interaction and stabilize an intermediate affinity state. To study the ability of the peptides to compete with endogenous Galphai proteins and block signal transduction in a native setting, we measured activation of G protein-coupled K+ channels through A1 adenosine or gamma-aminobutyric acid, type B, receptors in hippocampal CA1 pyramidal neurons. Native Galphai1/2, peptide, and certain analog peptides inhibited receptor-mediated K+ channel gating, dependent on which receptor was activated. This differential perturbation of receptor-G protein interaction suggests that receptors that act on the same G protein can be selectively disrupted