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First published online February 20, 2004
Journal of Experimental Biology 207, 1093-1099 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00852

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Intracellular calcium translocation during the contraction–relaxation cycle in scorpionfish swimbladder muscle

Suechika Suzuki^1,*, Naoki Hino² and Haruo Sugi¹

¹ Department of Physiology, School of Medicine, Teikyo University, 2-11-1, Kaga, Itabashi-ku, Tokyo 173-8605, Japan
² Department of Physiology, Juntendo Medical College of Nursing, 2-2, Takasu, Urayasu City, Chiba 279-0023, Japan

View larger version (114K): [in a new window]   Fig. 1. Arrangement of the SR components along the half sarcomere in SBM fibres. (A) Conventional electron micrograph of the fibre longitudinal section, showing the regular striation pattern (I, I band; Z, Z line; A, A band; H, H zone; M, M line) and regular arrangement of the SR components. LT, longitudinal tubules; FC, fenestrated collars; TC, terminal cisternae; T, transverse tubule. Bar, 2 µm. (B) Diagram illustrating the arrangement of the SR components and the five consecutive regions along the half sarcomere.

View larger version (143K): [in a new window]   Fig. 2. Typical longitudinal cryosection of an SBM fibre, exhibiting the regular striation pattern. Five consecutive regions along the half sarcomere (Z, I, A1, A2 and H) are indicated at the centre. The SR and T tubules are barely visible (arrows). Bar, 2 µm.

View larger version (29K): [in a new window]   Fig. 4. Ca distribution in the five regions at various stages in the contraction–relaxation cycle. Inset (top) is a diagram illustrating the six different stages of force change used for quick-freezing, i.e. at rest (A), during contraction (B), and at 0.1 s (C), 1 s (D), 3 s (E) and 5 s (F) after onset of relaxation. The bar shows period of stimulation (S). (A–F) [Ca] in the five regions along the half sarcomere. Values are means ± S.E.M. (N=36). Significant differences in [Ca] in the five regions are also shown; *P<0.05; ***P<0.001.

View larger version (17K): [in a new window]   Fig. 3. Distribution of Ca along the A–I boundary in the transverse direction. Note that the regions of high [Ca] are separated by those of low [Ca].