STUDIES ON ISOLATED SMOOTH MUSCLE CELLS. VII. RESPONSE TO AGONISTS AND THE CONTRACTION VELOCITY OF TAENIA COLI OF GUINEA PIG AND THE SINGLE SMOOTH MUSCLE CELLS

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Single smooth muscle cells were isolated from taenia coli of guinea pigs and degrees of responses of acetylcholine, histamine and prostaglandin E_2,and velocity of acetylcholinecontraction were compared with those of whole tissue. The contraction of single cells by these agonists were dose-dependent and ED_<50> of acetylcholine, histamine and prostaglandin E_2 were 0.3-1.1×10^<-6>, 5-11×10^<-7> and 1-3×10^<-9>M, respectively. These values were quite similar to those obtained with whole tissue. It took 2.0±0.2s for the single cells to be contracted completely by 10^<-4> M acetylcholine while it took 6.9±0.2s for the isotonic contraction of whole tissue. Times for a half maximum contraction, assuming that the whole tissue and the single cells were contracted at the maximum velocity, were 1.43±0.05 and 0.92±0.12s, respectively when 10^<-4>M acetylcholine was applied. These results revealed that response of muscle cells in the tissue to agonists was reflected on magnitude of the contraction of whole tissue and suggested that pharmacological properties of smooth muscle cells of taenia coli were not changed during the isolation procedure, whereas velocity of contraction of single cells was faster than that of whole tissue. Reasons for the difference in velocity were discussed.
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