Reduction of resting K+ current by metabotropic glutamate and muscarinic receptors in rat CA3 cells: mediation by G-proteins.
1. Effects of 1S,3R-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD) acting at metabotropic glutamate receptors (mGluRs), and methacholine (MCh), acting at cholinergic muscarinic receptors, were investigated in CA3 neurones in hippocampal slice cultures using the patch-clamp technique. 2. Both 1S,3R-ACPD (10 microM) and MCh (0.5 microM) activated an inward current associated with a decrease in membrane conductance. The current was observed when the slow calcium-dependent after-hyperpolarizing current (IAHP) and the voltage-dependent current (IM) were not activated, reversed close to the reversal potential for K+ (EK) (Erev = -92.8 +/- 10.7 and -89.2 +/- 8.6 mV for 1S,3R-ACPD and MCh, respectively), varied linearly with membrane potential, and thus corresponds to a leak K+ current. 3. The decrease in K+ conductance elicited with 1S,3R-ACPD (50 microM) was substantially reduced (> 70%) with bath application of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG, 1 mM), a selective mGluR antagonist and was not mimicked by the enantiomer 1R,3S-ACPD (100 microM). 4. The effects of 1S,3R-ACPD and MCh were mediated by activation of G-proteins since no inward current could be elicited in GDP beta S-loaded cells (500 microM). When cells were dialysed with GTP (100 microM) or GTP gamma S (250 microM), however, the amplitude of the current was significantly enhanced. 5. These findings provide evidence that G-proteins couple the activation of mGluRs and muscarinic receptors to a decrease in leak K+ conductance.
Guérineau
N C
NC
Brain Research Institute, University of Zürich, Switzerland.
Gähwiler
B H
BH
Gerber
U
U
D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D010084:Oxidation-Reduction; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*
D015221:Potassium Channels; D017470:Receptors, Glutamate; D011976:Receptors, Muscarinic; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D019204:GTP-Binding Proteins