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Voltage-dependent GABA-induced modulation of calcium currents in chick sensory neurons
1Department of Neurophysiology, Max Planck Institute for Psychiatry, Martinsried, F.R.G.
Abstract:
Externally applied gamma-aminobutyric acid (GABA) quickly and reversibly reduces by 60% voltage activated Ca2+ currents in chick dorsal root ganglion cells. This action is antagonized by depolarization, with characteristic time and voltage requirements. Intracellular perfusion with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) mimicks and blocks the GABA effect, respectively. A 3-state model describing the reactions involved is proposed.
Insights
Externally applied gamma-aminobutyric acid (GABA) significantly reduces Ca2+ currents in neurons. This neurotransmitter action is modulated by cellular conditions and involves specific guanine nucleotide interactions.
Area of Science:
- Neuroscience
- Cellular Biology
- Pharmacology
Background:
- Gamma-aminobutyric acid (GABA) is a primary inhibitory neurotransmitter in the central nervous system.
- Voltage-activated calcium (Ca2+) channels play crucial roles in neuronal excitability and neurotransmitter release.
- Understanding the precise mechanisms of GABAergic modulation on Ca2+ currents is vital for neuroscience research.
Purpose of the Study:
- To investigate the effect of externally applied GABA on voltage-activated Ca2+ currents in chick dorsal root ganglion cells.
- To elucidate the modulatory role of depolarization on GABA's action.
- To explore the involvement of intracellular guanine nucleotides in mediating GABA's effects.
Main Methods:
- Patch-clamp electrophysiology was used to measure voltage-activated Ca2+ currents.
- Cells were perfused intracellularly with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and guanosine 5'-O-(2-thiodiphosphate) (GDP beta S).
- Depolarization protocols were applied to assess antagonism of GABA's effects.
Main Results:
- External GABA application caused a rapid and reversible 60% reduction in Ca2+ currents.
- Depolarization antagonized the GABA effect with specific time and voltage dependencies.
- Intracellular GTP gamma S mimicked the inhibitory effect of GABA, while GDP beta S blocked it.
Conclusions:
- GABA exerts a direct inhibitory effect on voltage-activated Ca2+ currents in these neurons.
- The mechanism of GABA action involves intracellular signaling pathways dependent on guanine nucleotides.
- A 3-state model is proposed to describe the underlying reaction kinetics of GABAergic modulation.