Coexistence of GABAA and GABAB receptors on Aδ and C primary afferents

• Published in: British journal of pharmacology 1984-02, Vol.81 (2), p.327-333
• Main Authors: Désarmenien, Michel, Feltz, Paul, Occhipinti, Guiseppe, Santangelo, Francesca, Schlichter, Remy
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Animals; Biological and medical sciences; Calcium - physiology; gamma-Aminobutyric Acid - pharmacology; Ganglia, Spinal - drug effects; In Vitro Techniques; Medical sciences; Miscellaneous; Neural Conduction - drug effects; Neurons, Afferent - metabolism; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Pharmacology. Drug treatments; Rats; Receptors, Cell Surface - drug effects; Receptors, Cell Surface - isolation & purification; Receptors, GABA-A
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1984.tb10082.x

1 Intracellular recordings from adult rat dorsal root ganglion neurones were performed in vitro and the coexistence of two γ‐aminobutyric acid (GABA) receptors on the membrane of identified Aδ and C primary afferents was demonstrated. 2 Transient applications of GABA (10−6 − 10−2m) evoked dose‐dependent depolarizations and increased membrane conductance. The responses were mimicked by muscimol, isoguvacine, THIP and 3 amino propane sulphonic acid (3 APS); they were blocked by bicuculline and picrotoxin. Pentobarbitone induced an increase of GABA‐induced depolarizations. 3 Perfusion of tetraethylammonium (TEA, 7.5 mm) and intracellular injection of Cs+ ions unmasked the Ca2+ component of action potentials, which appeared as long‐lasting plateau depolarizations. Such action potentials were shortened in the presence of methoxyverapamil (D600, 5 × 10−6‐ 10−5m) and in a medium without Ca+ ions. 4 Prolonged (5–10 min) perfusion of GABA (10−9‐10−5m) shortened the Ca2+ component of action potentials. This effect was mimicked by baclofen (10−7‐5 × 10−6m) and muscimol (5 × 10−7‐10−5m) and was not affected by bicuculline perfusion (5 × 10−6‐10−5m). Isoguvacine (2.5 × 10−5m) did not affect action potential duration. 5 It is concluded that two GABA receptors coexist on the membrane of slow conducting primary afferents: the bicuculline‐sensitive GABAA receptor mediates depolarizations and the bicuculline‐insensitive GABAB receptor shortens the calcium component of action potentials.