Decrease in PIP2–channel interactions is the final common mechanism involved in PKC- and arachidonic acid-mediated inhibitions of GABAB-activated K+ current

Authors

  • Jong-Woo Sohn,

    1. National Research Laboratory for Cell Physiology and Department of Physiology, Seoul National University College of Medicine, Jongno-gu, Seoul 110–799, Korea
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  • Ajin Lim,

    1. National Research Laboratory for Cell Physiology and Department of Physiology, Seoul National University College of Medicine, Jongno-gu, Seoul 110–799, Korea
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  • Suk-Ho Lee,

    1. National Research Laboratory for Cell Physiology and Department of Physiology, Seoul National University College of Medicine, Jongno-gu, Seoul 110–799, Korea
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  • Won-Kyung Ho

    1. National Research Laboratory for Cell Physiology and Department of Physiology, Seoul National University College of Medicine, Jongno-gu, Seoul 110–799, Korea
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  • This paper has online supplemental material.

Corresponding author W.-K. Ho: Department of Physiology, Seoul National University College of Medicine, 28 Yonkeun-Dong, Jongno-gu, Seoul 110–799, Korea. Email: wonkyung@snu.ac.kr

Abstract

We showed in our previous study that in hippocampal CA1 neurons the stimulation of muscarinic receptors inhibited the GIRK current (IGIRK) via a PLC/PKC pathway, whereas group I metabotropic glutamate receptors (mGluR) inhibited IGIRK via a PLA2/arachidonic acid pathway. In this study, we present evidence that receptor-mediated signalling pathways activated by the two Gq-coupled receptors (GqPCRs) converge on the inhibition of GIRK channel–PIP2 interaction. IGIRK was activated in acutely isolated hippocampal CA1 neurons by repetitive application of baclofen, a GABAB receptor agonist, with a 2–3 min interval. When both CCh and DHPG were pretreated before the second IGIRK activation, the magnitude of the second IGIRK was 52.2 ± 2.5% of the first IGIRK, which was not significantly different from the magnitude of inhibition by CCh or DHPG alone. This result shows that the effects of muscarinic receptor and group I mGluR stimulation on IGIRK are not additive but occlusive, suggesting that each pathway may converge to a common mechanism that finally regulates IGIRK. To test the involvement of PIP2 in this mechanism, the effect of CCh and DHPG on IGIRK was tested in cells loaded with exogenous PIP2. The inhibition of IGIRK by CCh or DHPG was almost completely abolished in PIP2-loaded cells. We confirmed that the inhibition of IGIRK by direct application of phorbol ester or arachidonic acid was also completely reversed in PIP2-loaded cells. These results indicate that the decrease in PIP2–channel interactions is the final common mechanism responsible for GqPCR-induced inhibitions of IGIRK mediated by PKC and arachidonic acid.

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