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

Abstract

SUMMARY To examine intracellular Ca2+ translocation during the contraction–relaxation cycle in vertebrate striated muscle, electron probe X-ray microanalysis was performed on the swimbladder muscle (SBM) fibres of a scorpionfish Sebastiscus marmoratus. The SBM fibres were rapidly frozen at rest, during contraction and at various times after the onset of relaxation. Changes in calcium distribution in the components of the sarcoplasmic reticulum (SR) were examined on the SBM fibre cryosections. In resting fibres, the calcium concentration was highest around the boundary between the A and I bands (A–I boundary), where the terminal cisternae(TC) were located. In contracting fibres, the calcium concentration decreased around the A–I boundary, while it increased in all other regions of the sarcomere, indicating Ca2+ release from the TC into the myoplasm. During relaxation, the calcium concentration first increased around the regions, where the fenestrated collars (FC) and the longitudinal tubules (LT)were located, and then gradually returned to the levels seen in resting fibres. These results support the view that, after the onset of relaxation in the SBM fibres, Ca2+ in the myoplasm is first taken up by the FC and the LT, and then gradually returns to the TC.

Calsequestrins in skeletal and cardiac muscle from adult Danio rerio

“…If the previous speculations were true, the fluorescence patterns could suggest that cardiac Casq is more strictly anchored to terminal cisternae and the skeletal isoforms are more freely distributed between the junctional and longitudinal SR. It is interesting to note that Suzuki et al (2004) found that Ca 2? during relaxation is accumulated in fenestrate SR of scorpion fish muscle suggesting that a calcium binding protein located in this SR compartment might be involved in muscle relaxation.…”

Electrical and mechanical properties and mode of innervation in scorpionfish sound-producing muscle fibres

“…Recently, Suzuki et al (2003) showed that the SBM fibres of scorpionfish contain extremely well developed sarcoplasmic reticulum (SR), indicating that the rapid twitch associated with rapid relaxation may be due to a rapid rate of Ca 2+ uptake by the SR. Using techniques of quick freezing and energy dispersive X-ray microanalysis of cryosections, Suzuki et al (2004) also studied the mode of intracellular Ca 2+ translocation in the SBM fibres. Nevertheless, how the mechanical activity of the SBM fibres is controlled by motor nerve impulses during sound production still remains obscure.…”