X-ray Microanalysis Studies on the Calcium Localization along the Inner Surface of Plasma Membranes in the Anterior Byssus Retractor Muscle of Mytilus edulis
To investigate the role of plasma membranes in the regulation of intracellular Ca translocation in smooth muscles, the intracellular Ca localization in the anterior byssus retractor muscle (ABRM) of Mytilus edulis was examined by the quantitative X-ray microanalysis of cryosections. When the spot analysis was carried out successively along the plasma membrane in the cryosections of resting ABRM fibers, significant amounts of Ca (～8 mmol/kg dry wt) were frequently detected, although in some cases the Ca concentration was negative. Averaged Ca concentration detected was approximately 3.0 mmol/kg dry wt (n=25), while the Ca concentration was negligible at the myoplasm. By the pyroantimonate method including the semi-quantitative X-ray microanalysis, the intracellular Ca localization and its translocation during the contraction were also observed. These results indicate that, in the ABRM fibers, the plasma membranes accumulate Ca on their inner surface, and release Ca to cause contraction
