Inhibition of muscarinic receptor-operated Ca2+ sensitization by short-term desensitization of alpha-toxin-permeabilized smooth muscle cells from guinea pig stomach.
1. Isolated single smooth muscle cells from the guinea pig stomach were permeabilized with Staphylococcus aureus alpha-toxin. 2. The permeabilized single cells showed a shortening in response to Ca2+ in an all-or-none manner. Moreover, the addition of acetylcholine (ACh) or guanosine 5'-triphosphate (GTP) resulted in a decrease in concentration of Ca2+ required to trigger a threshold response, suggesting that Ca2+ sensitization is induced by the stimulation of muscarinic acetylcholine receptors (mAChRs) or GTP-binding protein(s). 3. Short-term desensitization was induced by incubating the permeabilized cells with 100 microM ACh for 10 min. 4. In desensitized cells, the concentration of Ca2+ required to trigger a threshold response in the presence of ACh was increased, however, the cell shortening in response to Ca2+ in the absence of ACh and GTP-induced Ca2+ sensitization was not affected by short-term desensitization. 5. These results suggest that the receptor-operated augmentation of Ca2+ sensitivity is inhibited by short-term desensitization and that the development of short-term desensitization is due to an uncoupling of mAChR/GTP-binding protein(s).
Mita
M
M
Department of Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Satoh-Akimoto
K
K
Oishi
K
K
Hashimoto
T
T
Uchida
M K
MK
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D005748:Gastric Fundus / Q000166:cytology / Q000187:drug effects; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D013270:Stomach / Q000166:cytology / Q000187:drug effects*; D010738:Type C Phospholipases / Q000494:pharmacology*
D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D000109:Acetylcholine; D002118:Calcium