Activation of heteromeric G protein-gated inward rectifier K ⁺ channels overexpressed by adenovirus gene transfer inhibits the excitability of hippocampal neurons

Abstract

G protein-gated inward rectifier K ؉ channel subunits 1-4 (GIRK1-4) have been cloned from neuronal and atrial tissue and function as heterotetramers. To examine the inhibition of neuronal excitation by GIRKs, we overexpressed GIRKs in cultured hippocampal neurons from 18 day rat embryos, which normally lack or show low amounts of GIRK protein and currents. Adenoviral recombinants containing the cDNAs for GIRK1, GIRK2, GIRK4, and the serotonin 1A receptor were constructed. Typical GIRK currents could be activated by endogenous GABA B , serotonin 5-HT 1A , and adenosine A1 receptors in neurons coinfected with GIRK1؉2 or GIRK1؉4. Under current clamp, GIRK activation increased the cell membrane conductance by 1-to 2-fold, hyperpolarized the cell by 11-14 mV, and inhibited action potential firing by increasing the threshold current for firing by 2-to 3-fold. These effects were not found in non-and mock-infected neurons, and were similar to the effects of muscarinic stimulation of native GIRK currents in atrial myocytes. Two inhibitory effects of GIRK activation, hyperpolarization and diminution of depolarizing pulses, were simulated from the experimental data. These inhibitory effects are physiologically important in the voltage range between the resting membrane potential and the potential where voltage-gated Na ؉ and K ؉ currents are activated; that is where GIRK currents are outward.

Fast noninvasive activation and inhibition of neural and network activity by vertebrate rhodopsin and green algae channelrhodopsin

“…2D and 1C) probably because of the effect of endogenous proteins, such as RGS proteins, which accelerate the GTPase activity of the G proteins. These observations are comparable to the described actions of Gi͞o-coupled receptors on membrane changes in neurons (20). More importantly, the hyperpolarization induced by light was capable of reducing the number of action potentials produced during a depolarizing current pulse ( Fig.…”

Suppression of Neuronal Hyperexcitability and Associated Delayed Neuronal Death by Adenoviral Expression of GABACReceptors

“…Overexpression of a chloride transporter, forcing the chloride reversal potential to become more negative (Staley et al, 1996), is another approach. Excitability can be reduced by viral expression of inwardly rectifying potassium channels with a consequent increase in the threshold for action potential generation (Ehrengruber et al, 1997;Johns et al, 1999). Because activation of the classical MAP kinases (Murray et al, 1998) may mediate delayed neuronal death, expression of a dominant-negative MAP kinase mutant might render neurons resistant to excitotoxic death.…”

γ-Aminobutyric acid type B receptors are expressed and functional in mammalian cardiomyocytes

“…Our findings are reminiscent of observations reported for neurons or heterologous expression vectors (10,13,(19)(20)(21)(22)(23)(24)(25)36), in that both GHB (at millimolar concentrations) and baclofen (at micromolar Northern blot analysis of GABA BR1a and -R1b transcripts in rat cardiomyocytes (Heart) and hippocampal tissue (Brain). Receptor mRNAs were amplified by RT-PCR, using primers specific to the different 5Ј ends of the two isoforms, and the products were size fractionated on 2% agarose gels for comparison with a 100-bp DNA ladder (first lane).…”

“…Indeed, the electrophysiological changes after GABA B agonist application, and the strong inwardly rectifying property of the GHB-induced current (Fig. 1C) together with its sensitivity to Ba 2ϩ , suggest that this current might be caused by the opening of Kir3 channels as described for postsynaptic inhibition after GABA B R activation (20)(21)(22)(23)(24)(25). Assuming that Kir3 channels might be the final effectors in cardiomyocytes could have been in contradiction to the classical notion that these channels are absent from mammalian ventricle (39).…”

“…In contrast, the GABA B agonist baclofen induces quite similar effects, with an EC 50 of 3-5 M for GABA B R-activated inwardly rectifying K ϩ currents (20,21). As a matter of fact, several studies have borne out the conclusion that inwardly rectifying K ϩ channels of subfamily 3 (Kir3) are prominent postsynaptic effectors of GABA B receptors in neuronal tissue (19)(20)(21)(22)(23)(24)(25).…”