Modulation of calcium currents by a metabotropic glutamate receptor involves fast and slow kinetic components in cultured hippocampal neurons.
The modulation of high-threshold Ca2+ currents by the selective metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), was investigated in cultured hippocampal neurons using whole-cell voltage-clamp recording. ACPD reduced high-threshold Ca2+ currents carried by Ba2+ with an EC50 of 15.5 microM. The inhibition was reversible, voltage dependent, and blocked by L-2-amino-3-phosphonopropionic acid (1 mM) or by pretreatment with pertussis toxin. Inhibition by ACPD was greatly enhanced, and became irreversible, when the nonhydrolyzable GTP analog GTP gamma S was included in the whole-cell pipette. In some neurons, the Ba2+ current was inhibited by L(+)-2-amino-4-phosphonobutanoic acid (L-AP4) as well as ACPD while most cells were insensitive to L-AP4, suggesting that these agonists activate distinct receptors. The inhibition of Ca2+ currents was reduced but not eliminated in the presence of either omega-conotoxin GVIA or nifedipine, suggesting that both N- and L-type Ca2+ currents were affected. The degree and kinetics of inhibition were dependent on intracellular calcium. With [Ca]i < 1 nM, inhibition had a fast onset (t approximately 1-2 sec) and a rapid recovery, consistent with a membrane-delimited pathway. However, a slow component of inhibition appeared when the steady state [Ca]i was increased to 100 nM (t onset approximately 3 min). The slow component did not require transient Ca2+ influx or release of intracellular Ca2+. We suggest that Ca2+ channel modulation by ACPD involves either two mGluR subtypes with separate coupling mechanisms or a single mGluR that couples to both mechanisms.
Vollum Institute, Oregon Health Sciences University, Portland 97201.
Y
Y
Sahara
G L
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Westbrook
D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001464:Barium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D003517:Cyclopentanes / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology / Q000379:methods; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006624:Hippocampus / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D037342:Pertussis Toxin; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology* / Q000502:physiology; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D003517:Cyclopentanes; D010455:Peptides; D017470:Receptors, Glutamate; D010566:Virulence Factors, Bordetella; C000211:2-amino-3-phosphonopropionic acid; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C075501:3-aminocyclopentane-1-carboxylic acid; D020866:omega-Conotoxin GVIA; D037342:Pertussis Toxin; D009543:Nifedipine; D000409:Alanine