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5-Hydroxytryptamine facilitates GABA-induced depolarization in bullfrog primary afferent neurons
1Department of Physiology, Kurume University School of Medicine, Japan.
Abstract:
Intracellular and voltage-clamp recordings were made from sensory neurons in bullfrog dorsal root ganglia (DRG). Bath-application of 5-hydroxytryptamine (5-HT, 10 microM to 1 mM) reversibly increased the amplitude of depolarizing responses to gamma-aminobutyric acid (GABA) and muscimol. 5-HT also increased the amplitude of chloride current activated by GABA. An analysis with dose-response curves revealed that 5-HT potentiated the maximum GABA current (Vmax), while it produced no significant change in the apparent dissociation constant (Km). It is suggested that 5-HT increases the sensitivity of the GABAA receptor, acting on an allosteric site for the receptor-ionophore complex.