G protein-mediated inhibition of phosphoinositide metabolism evoked by metabotropic glutamate receptors in frog oocytes.
1. Metabotropic glutamate receptor subtype 1 (mGluR1), when expressed in Xenopus oocytes, activates phosphoinositide-specific phospholipase C (PLC) in a G protein-dependent manner. This reaction results in the activation of chloride channels in the oocytes, and can be monitored electrophysiologically. We expressed different G protein alpha-subunits together with mGluR1 in oocytes, and examined the effects of these G protein subunits on the PLC-mediated reaction. 2. The expression of the alpha-subunit of GL2, a bovine version of G11, which is a member of the Gq subgroup, potentiated the mGluR1-evoked reaction, whereas the alpha-subunit of GL1, a bovine G14, which is also a member of the Gq subgroup, strongly suppressed it. The expression of Gs alpha also suppressed this reaction. 3. We then expressed G beta 1 gamma 2-subunits in addition to the G alpha-subunits, and examined the mGluR1-evoked reactions. Both the potentiation and suppression by GL2 alpha and GL1 alpha, respectively, were more pronounced in the presence of the G beta 1 gamma 2-subunits. In contrast, the suppression by Gs alpha was completely reversed by G beta 1 gamma 2. 4. The direct activation of G proteins by the intracellular injection of either fluoride ions or guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S) causes similar PLC-mediated reactions. The expression of GL2 alpha, GL1 alpha or Gs alpha caused potentiation, suppression and no change, respectively, on the fluoride- (or GTP gamma S-) evoked reactions.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan.
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K
Nakamura
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T
Nukada
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T
Haga
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H
Sugiyama
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D004594:Electrophysiology; D004789:Enzyme Activation; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism; D014982:Xenopus laevis
D017931:DNA Primers; D010716:Phosphatidylinositols; D018094:Receptors, Metabotropic Glutamate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins