Ethanol inhibits the function of 5-hydroxytryptamine type 1c and muscarinic M1 G protein-linked receptors in Xenopus oocytes expressing brain mRNA: role of protein kinase C.
Effects of ethanol on the function of Ca(2+)-activated Cl- channels activated by G protein-coupled serotonin (5-hydroxytryptamine, (5-HT)1c) and muscarinic M1 cholinergic receptors were studied in Xenopus oocytes expressing mouse whole-brain mRNA. Ethanol (25-200 mM) inhibited currents evoked by both 5-HT and acetylcholine (ACh), in a concentration-dependent manner. The maximal effect was obtained with 150 mM ethanol, which produced 65 and 49% inhibition of 5-HT and ACh responses, respectively. In the presence of 100 mM ethanol, the EC50 values for both 5-HT and ACh were increased about 4-fold. In contrast, in oocytes expressing rat cerebellar mRNA, metabotropic glutamate receptor responses were much less sensitive to ethanol. To examine potential postreceptor sites for ethanol inhibition, guanosine-5'-O-(3-thio)triphosphate and myo-inositol-1,4,5-trisphosphate were injected intracellularly. Ethanol (100 mM) did not significantly inhibit the currents produced by either guanosine-5'-O-(3-thio)triphosphate or myo-inositol-1,4,5-trisphosphate. Activation of protein kinase C (PKC) by phorbol-12-myristate-13-acetate markedly inhibited 5-HT-induced responses. Both the PKC inhibitor peptide and staurosporine prevented ethanol inhibition of 5-HT-induced responses. Moreover, ethanol, similarly to phorbol-12-myristate-13-acetate and opposite to PKC inhibitors, enhanced the rate of Ca(2+)-activated Cl- current desensitization induced by repeated applications of 5-HT. These results indicate that certain types of receptor-G protein interactions are more susceptible than others to uncoupling by ethanol and that ethanol inhibition of 5-HT1c receptors requires PKC-mediated phosphorylation. We suggest that ethanol may activate PKC, which phosphorylates the receptors, resulting in inhibition of the responses.
Sanna
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Department of Pharmacology, University of Colorado Health Sciences Center, Denver 80262.
Dildy-Mayfield
J E
JE
Harris
R A
RA
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D000431:Ethanol / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018727:Muscarinic Antagonists; D009865:Oocytes; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism; D015290:Second Messenger Systems / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists; D014982:Xenopus laevis
D002712:Chlorides; D018727:Muscarinic Antagonists; D012333:RNA, Messenger; D018094:Receptors, Metabotropic Glutamate; D011976:Receptors, Muscarinic; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000431:Ethanol; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D002118:Calcium