Coexistence of GABAA and GABAB receptors on A delta and C primary afferents.
Intracellular recordings from adult rat dorsal root ganglion neurones were performed in vitro and the coexistence of two gamma-aminobutyric acid (GABA) receptors on the membrane of identified A delta and C primary afferents was demonstrated. Transient applications of GABA (10(-6)-10(-2) M) 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. 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 X 10(-6)-10(-5) M) and in a medium without Ca+ ions. Prolonged (5-10 min) perfusion of GABA (10(-9)-10(-5) M) shortened the Ca2+ component of action potentials. This effect was mimicked by baclofen (10(-7)-5 X 10(-6) M) and muscimol (5 X 10(-7)-10(-5) M) and was not affected by bicuculline perfusion (5 X 10(-6)-10(-5) M). Isoguvacine (2.5 X 10(-5) M) did not affect action potential duration. 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.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D005727:Ganglia, Spinal / Q000187:drug effects; D066298:In Vitro Techniques; D009431:Neural Conduction / Q000187:drug effects; D009475:Neurons, Afferent / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000302:isolation & purification*; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D002118:Calcium