Carbachol-induced secretion and homologous desensitization in rat basophilic leukemia (RBL-2H3) cells transfected with human m2 muscarinic acetylcholine receptors.
Carbachol (CCh) caused a dose-dependent release of beta-hexosaminidase and an increase in the production of inositol 1,4,5-trisphosphate (IP3) in RBL-2H3 cells transfected with m2 mAChR cDNA (RBL-m2 cells). The secretion was completely inhibited by LaCl3 and pertussis toxin. The secretion was dependent on extracellular Ca2+ and mediated through the pertussis toxin-sensitive G protein. Exposing RBL-m2 cells to 100 microM CCh for 30 min in Ca2+ -free medium (desensitizing treatment) inhibited the secretion induced by the subsequent addition of 10 microM CCh plus Ca2+, but not by stimulating the high affinity IgE receptor (FcepsilonRI). Desensitizing treatment of RBL-m2 cells reduced the affinity of the lipophilic ligand [3H]quinuclidinyl benzilate to m2 mAChR without a reduction of the total m2 mAChR number. The treatment also decreased the cell surface mAChR number to 14% with a slight reduction in its affinity. Desensitizing treatment of RBL-m2 cells inhibited the CCh-induced transient increase in levels of IP3 and intracellular Ca2+ concentration. The results suggested that the CCh-induced desensitization of m2 mAChR-mediated secretion is due to the receptor sequestration followed by blocking the increase in [Ca2+]i and that this desensitizing mechanism is receptor-subtype-specific.
Oishi
Kazuhiko
K
Department of Pharmacology, Meiji Pharmaceutical University, Kiyose, Tokyo, Japan. oishikz@my-pharm.ac.jp
Sakurai
Akihiro
A
Seki
Noriyasu
N
Yoshizumi
Tomokazu
T
Uchida
Masaatsu K
MK
D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D015471:Leukemia, Basophilic, Acute / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D043585:Receptor, Muscarinic M2 / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D014162:Transfection / Q000379:methods*; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism*
D043585:Receptor, Muscarinic M2; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D001619:beta-N-Acetylhexosaminidases