抄録
It has been established that the contractile system in cerebral vascular smooth muscle involves myosin and actin, which form thick and thin filaments, respectively and that their activities are regulated by the intracellular free Ca2+ concentration. The membrane system, both the cell surface and intracellular organelles, seems to be responsible for controlling the myoplasmic Ca2+ level.
An attempt was made to show the localization of intracellular Ca2+, which might play a key role on the regulation of contractile elements in bovine cerebral arteries. The pyroantimonate precipitate method was used. For quantitative chemical analysis of the pyroantimonate precipitates, the sections were analyzed with an energy dispersive X-ray microanalyzer (EDAX 711) attached to a transmission scanning electron microscope; the output of the analyzer was processed by a computer system. A distinct peak at 3, 620 eV, which was considered as a combined peak of Sb-Lα and Ca-Kα lines, was always observed in all the precipitates examined, indicating that the precipitates may serve as a valid measure of Ca2+ localization.
When the muscle cells were fixed after 50 minutes of soaking in high-K Krebs solution (127 mM-K substituted for Na) containing 10.8 mM Ca, the precipitates were mostly observed at the plasma membrane, the sarcoplasmic reticulum, the mitochondria and the nuclei. It was not, however, possible to decide whether the precipitates on the plasma membrane were located on its inner surface or its outer surface. In this condition, the muscle cells were completely relaxed during fixation.
If the preparations were fixed without pretreatment, they showed marked tension development in response to the pyroantimonate-osmium solution. The precipitates were mostly distributed randomly in the myoplasm of the muscle cells fixed during mechanical activity, while the precipitates were rarely seen at the plasma membrane, the sarcoplasmic reticulum and the mitochondria.
The results obtained in these experiments are in general agreement with previous reports on different kinds of smooth muscles, strongly suggesting that the Ca2+ accumulated at the plasma membrane, the sarcoplasmic reticulum and the mitochondria is released into the myoplasm to cause contraction in bovine cerebral arterial smooth muscle.
