Activation of Protein Kinase C Induces Internalization of the GABA<sub>C</sub> Receptors Expressed in Xenopus Oocytes

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  • Activation of Protein Kinase C Induces Internalization of the GABAc Receptors Expressed in Xenopus Oocytes

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Abstract

In a previous study, we showed that the protein kinase C (PKC) activator 4β-phorbol 12-myristate 13-acetate (PMA) inhibited the γ-aminobutyric acid (GABA)–gated currents in Xenopus oocytes expressing human ρ1 GABAC receptors. To investigate whether the inhibition of currents was due to a decrease in efficacy or in the potency of ρ1 GABAC receptor, concentration-response curves for GABA were compared before and after PMA treatment. The EC50 concentrations of GABA obtained during the maximally inhibited period were not statistically different from the concentrations obtained before PMA treatment (1.74 ± 0.33 and 1.45 ± 0.28 μM, respectively). These results indicate that the inhibition depends on a change in number or conductance of active receptor channels, but not on a change in affinity for GABA. To allow histochemical detection of ρ1 GABAC receptors, we constructed a receptor tagged at the C-terminal position with human c-myc epitope. Electrophysiologically, the tagged receptors showed almost the same sensitivities for GABA and PMA as those of wild-type ρ1 GABAC receptors. Immunohistochemistry with anti-myc antibody detected a dense concentration of tagged receptors at the surface area of Xenopus oocytes. Transient exposure to PMA reduced the density of immunofluorescence at the surface area and increased it in the subsurface area. These results suggest that the stimulation of protein kinase C leads to internalization of ρ1 GABAC receptors expressed in Xenopus oocytes.<br>

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