All-or-none augmentation of Ca2+ sensitivity in alpha-toxin-permeabilized single smooth muscle cells from guinea-pig taenia caecum.
1. Isolated smooth muscle cells from guinea-pig taenia caecum were permeabilized by use of Staphylococcus aureus alpha-toxin, and the sarcoplasmic reticulum Ca2+ store was depleted by exposure to 0.1 microM A23187. 2. Shortening of alpha-toxin-permeabilized single smooth muscle cells was induced by increasing free Ca2+ but was not induced by 0.2 microM free Ca2+. 3. Shortening of the permeabilized cells was caused by application of acetylcholine (ACh) with free Ca2+ concentration held at 0.2 microM. Permeabilized smooth muscle cells responded to 0.3 microM or 1 microM ACh with 0.2 microM Ca2+ with maximal shortening. The concentration-response relationship to ACh had a very steep slope and the cell shortening appeared to be an all-or-none response rather than a graded response, as was the shortening of intact cells to ACh. 4. The shortening of permeabilized cells was also induced by application of guanosine 5'-triphosphate (GTP) with 0.2 microM free Ca2+, showing an all-or-none response. The threshold concentration of GTP that induced an all-or-none response was between 10 microM and 30 microM. 5. These results suggest that Ca2+ sensitivity is augmented by stimulation of the muscarinic receptor or GTP-binding protein(s) in an all-or-none manner. It seems probable that this contributes to the all-or-none response to ACh in intact smooth muscle cells.
Mita
M
M
Department of Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Hashimoto
T
T
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001427:Bacterial Toxins / Q000633:toxicity*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002432:Cecum / Q000166:cytology / Q000187:drug effects*; D002463:Cell Membrane Permeability / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D006460:Hemolysin Proteins / Q000633:toxicity*; D007476:Ionophores / Q000494:pharmacology; D008858:Microscopy, Phase-Contrast; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D013211:Staphylococcus aureus
D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D007476:Ionophores; D011976:Receptors, Muscarinic; C021091:staphylococcal alpha-toxin; D000001:Calcimycin; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D002118:Calcium