Impairment of GABAA receptor function by N-methyl-D-aspartate-mediated calcium influx in isolated CA1 pyramidal cells

Neuroscience. 1994 Oct;62(3):813-28. doi: 10.1016/0306-4522(94)90479-0.

Abstract

Mechanisms of regulation of GABAA receptor function by intracellular calcium ([Ca2+]i) were examined in cell somata and apical dendrites of pyramidal cells, acutely dissociated from the CA1 hippocampal subfield of adult guinea-pigs. GABAA receptor-mediated currents were measured by whole-cell clamp recordings. N-methyl-D-aspartate receptor-mediated currents were used as conditioning source of calcium influx. Peak amplitudes of somatic GABAA whole-cell currents were reduced to about 15% of control values when net inward charge accumulation by N-methyl-D-aspartate currents reached 1.85 nC. A similar decline of GABAA currents was observed in dendritic recordings. The N-methyl-D-aspartate-mediated reduction of somatic and dendritic GABAA currents was accompanied by a well correlated decrease in peak and chord conductances. Pharmacological blockade of N-methyl-D-aspartate currents by 2-amino-5-phosphonopentanoic acid prevented the N-methyl-D-aspartate-mediated suppression of GABAA responses. The N-methyl-D-aspartate effect was mediated by the calcium component of N-methyl-D-aspartate receptor-mediated currents as demonstrated by a lack of effect in the absence of extracellular calcium and faster N-methyl-D-aspartate-mediated suppression of GABAA responses in lower intracellular 1,2-bis(2-aminophenoxy)ethane-N,N,N',N"-tetra-acetate. N-methyl-D-aspartate-mediated suppression of GABAA currents was significantly less expressed when intracellular ATP was replaced by its analog adenosine 5'-O-(3-thiotriphosphate) and when the specific phosphatase 2B inhibitor cypermethrin was added intracellularly. The reduction of GABAA responses persisted after cessation of N-methyl-D-aspartate-mediated calcium influx, indicating a long-term action of N-methyl-D-aspartate on GABAA responses. Voltage-activated calcium currents did not affect GABAA responses under the experimental conditions applied. In conclusion, the data presented show that calcium influxes through N-methyl-D-aspartate receptor channels result in long-term suppression of GABAA receptor function in CA1 pyramidal cells. Intracellular mechanisms of N-methyl-D-aspartate-mediated reduction of GABAA conductances involve activation of phosphatase 2B and consecutive dephosphorylation of the GABAA receptor or a closely associated GABAA receptor-regulating enzyme. Possible mechanisms of such a distinct N-methyl-D-aspartate-dependent calcium signalling pathway in the dephosphorylation-dependent suppression or GABAA receptor function are discussed.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / analogs & derivatives
  • Adenosine Triphosphate / pharmacology
  • Animals
  • Biological Transport / drug effects
  • Calcium / physiology*
  • Calcium Channels / drug effects*
  • Calcium Channels / physiology
  • Calmodulin / physiology
  • Chloride Channels / drug effects
  • Chloride Channels / physiology
  • Dendrites / drug effects
  • Dendrites / physiology
  • Egtazic Acid / analogs & derivatives
  • Egtazic Acid / pharmacology
  • GABA-A Receptor Antagonists*
  • Guinea Pigs
  • Hippocampus / cytology
  • Intracellular Fluid
  • N-Methylaspartate / pharmacology*
  • Nerve Tissue Proteins / drug effects
  • Nerve Tissue Proteins / physiology*
  • Phosphoprotein Phosphatases / physiology
  • Phosphorylation / drug effects
  • Protein Processing, Post-Translational / drug effects
  • Pyramidal Cells / drug effects*
  • Pyramidal Cells / metabolism
  • Receptors, GABA-A / physiology
  • Receptors, N-Methyl-D-Aspartate / drug effects*
  • Signal Transduction

Substances

  • Calcium Channels
  • Calmodulin
  • Chloride Channels
  • GABA-A Receptor Antagonists
  • Nerve Tissue Proteins
  • Receptors, GABA-A
  • Receptors, N-Methyl-D-Aspartate
  • adenosine 5'-O-(3-thiotriphosphate)
  • Egtazic Acid
  • N-Methylaspartate
  • Adenosine Triphosphate
  • Phosphoprotein Phosphatases
  • 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
  • Calcium