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All‐or‐none augmentation of Ca 2+ sensitivity in c‐toxin‐permeabilized single smooth muscle cells from guinea‐pig taenia caecum
Author(s) -
Mita Mitsuo,
Hashimoto Takao
Publication year - 1995
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1995.tb16365.x
Subject(s) - biology , taenia coli , caecum , acetylcholine , muscle contraction , gtp' , endoplasmic reticulum , medicine , biophysics , endocrinology , stimulation , muscarinic acetylcholine receptor , calcium , guinea pig , biochemistry , receptor , enzyme
1 Isolated smooth muscle cells from guinea‐pig taenia caecum were permeabilized by use of Staphylococcus aureus α ‐toxin, and the sarcoplasmic reticulum Ca 2+ store was depleted by exposure to 0.1 μ M A23187. 2 Shortening of α‐toxin‐permeabilized single smooth muscle cells was induced by increasing free Ca 2+ but was not induced by 0.2 μ M free Ca 2+ . 3 Shortening of the permeabilized cells was caused by application of acetylcholine (ACh) with free Ca 2+ concentration held at 0.2 μ M . Permeabilized smooth muscle cells responded to 0.3 μ M or 1 μ M ACh with 0.2 μ M Ca 2+ 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 μ M free Ca 2+ , showing an all‐or‐none response. The threshold concentration of GTP that induced an all‐or‐none response was between 10 μ M and 30 μ M . 5 These results suggest that Ca 2+ 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.