Electron-probe x-ray microanalysis studies on the intracellular calcium translocation during the contraction-relaxation cycle in the fish swimbladder muscle

The swimbladder muscle of a teleost fish,Sebasticus marmoratus, contracts rapidly to produce sounds for communication and contains extremely well developed sarcoplasmic reticulum (SR), providing a material suitable for studying the intracellular Ca translocation during the contraction-relaxation cycle. We examined the change of Ca distribution along the sarcomere at various states of the fibers during the contractionrelaxation cycle in the swimbladder muscle by means of quantitative electron probe X-ray microanalysis of cryosections. The muscle fibers were rapidly frozen at rest, during sustained contraction and at 0.1 and 1.0 sec after the onset of relaxation with a dual-jet liquid propane freezing device. Cryosections (200 nm thick) were cut from the middle portion of the frozen fibers at -110°C on a LKB NOVA cryoultramicrotome, and placed on thin carbon supporting films on Nigrids. Then the cryosections were freeze-dried at 10-6torr and below -80°C. Electron probe X-ray microanalysis was performed on a liquid N2-cooled Be-stage at -130°C in a JEOL 2000FX electron microscope operated at 80 kV and equipped with a Tracor Northern TN5500 energy dispersive X-ray microanalyzer.