Effects of transient oxygen-glucose deprivation on G-proteins and G-protein-coupled receptors in rat CA3 pyramidal cells in vitro.
The role of guanosine triphosphate-binding proteins (G-proteins) in the generation of the outward current during transient oxygen-glucose deprivation (OGD) was investigated in CA3 pyramidal cells in rat hippocampal organotypic slice cultures using the single-electrode voltage-clamp technique with KMeSO4-filled microelectrodes. To simulate ischaemia, brief chemical OGD (2 mM 2-deoxyglucose and 3 mM NaN3 for 4-9 min) was used, which induced an outward K+ current associated with an increase in input conductance. OGD failed to induce the outward current under conditions where G-protein function was disrupted by loading cells with guanosine 5'-O-(2-thiodiphosphate) [GDPbetaS] or after prolonged injection of guanosine 5'-O(3-thiotdphosphate) [GTPgammaS]. However, in slices treated with pertussis toxin (PTX), OGD still elicited the outward current, indicating that PTX-insensitive G-proteins are involved. Consistent with this insensitivity to PTX, neither adenosine receptors nor GABA(B) (gamma-aminobutyric acid) receptors, which operate via PTX-sensitive G-proteins, mediate the OGD-induced outward current. When adenosine receptors or GABA(B) receptors were blocked with 1,3-dipropyl-8-psulphophenylxanthine (DPSPX, 5 microM) or CGP 52 432 (10 microM), respectively, the OGD-induced response was not modified. The response also persisted following pretreatment of slice cultures with tetanus toxin to prevent vesicular release of neurotransmitters and neuromodulators from presynaptic terminals. Both PTX-sensitive and PTX-insensitive G-protein-mediated responses were suppressed during OGD. The inward current induced by the metabotropic glutamate receptor agonist 1 S, 3R-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD) and the outward current elicited by adenosine or baclofen were strongly or completely attenuated. In contrast, the ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) response was not affected. These findings suggest that during OGD there is a functional uncoupling of receptors from G-proteins, and a direct receptor-independent activation of PTX-insensitive G-proteins leading to an increase in membrane K+ conductance.
Tanabe
M
M
Brain Research Institute, University of Zurich, Switzerland.
Gähwiler
B H
BH
Gerber
U
U
D000241:Adenosine / Q000502:physiology; D000818:Animals; D004553:Electric Conductivity; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005947:Glucose / Q000172:deficiency*; D000860:Hypoxia / Q000378:metabolism*; D009924:Organ Culture Techniques; D017966:Pyramidal Cells / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011956:Receptors, Cell Surface / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D011956:Receptors, Cell Surface; D005680:gamma-Aminobutyric Acid; D019204:GTP-Binding Proteins; D005947:Glucose; D000241:Adenosine