Na^+欠乏環境中における平滑筋の活動電位
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概要
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The transmembrane action potential of a smooth muscle cel taken from the ureter of Cavia cobaya was picked up by an intraaacellular electrode, observed on a cathode ray oscillograph, and its configurations recorded. The action potential appearred often spontaneously, but it could be evoked also by artificial stimulation. The action potential consisted of both a slow potential with a long plateau as well as rapid oscillating spike potentials. In typical cases, the latter was superposed on the initial part of the former. But often only one of the components appeared, separately from the other. The slow potential lacking the oscillating spike potentials was evoked often after frequent stimulations. To prepare the sodium deficient medium, a part of the NaCl of the Krebs solution in which the ureter was soaked was substituted by an isotonic tetraethyl ammonium bromide (TEA), choline chloride or sucrose solution. In the TEA-Krebs solution, the oscillatory spike potentials diminished and only the slow potential remained, which was very similar in appearance to the action potential of the amphibian heart ventricle, i.e., first a rapid elevation was observed, followed by a palteau of long duration and gradual decay. These results were observed even when only a small part of the NaCl was substituted by TEA. A remarkable lowering of the slow component of the ureter action potential occured in choline-Krebs solution. As a result, only several of the spike potentials remained. The frequency of the oscillating spike potentials decreased and the duration of the single spike was elongated and its amplitude increased. Similar efects were also observed in the sucrose-Krebs solution. When a large part of the NaCl of Krebs-solution was substituted by the above mentioned substances, spontaneous excitations were often aroused, and action potentials of changed configuration appeared. It is well known that the application of TEA to skeletal muscles evokes repetitive excitations. It is interesting that TEA also causes repetitive excitations in smooth muscle fibers.The duration of the spontaneous slow action potential evoked in TEA-Krebs solution was very much elongated. In the choline-Krebs solution also, spontaneous action potential appeared, but in this case, the configuration was that of a spike potential and each was preceded by a slowly elevating small prepotential. In a sodium deficient medium, the configuration of the action potentials of the Cavia ureter was exceedingly altered, and the two components i.e., slow potential and rapidly oscillating potentials could be separated. From such facts it may be concluded that the mechanism for the generation of the two components of the action potential are also quite different from each other. The validity of the Hodgkin's sodium theory on the action potential of the smooth muscle is problematic.
- 社団法人日本動物学会の論文
- 1964-08-15