QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

Cover  The two freeze-fracture images show the clustering and disposition of L-type calcium channels (dihydropyridine receptors or DHPR) in T tubules from fish skeletal muscle (top) and in the surface membrane from a skeletal muscle-derived mouse cell line (bottom). The arrangement of DHPRs into arrays of tetrads (or groups of four) is dictated by the stereospecific linkage between DHPRs and the four equal subunits of the ryanodine receptor, or RyR. RyR are the calcium-release channels of the internal membrane system, or sarcoplasmic reticulum (SR); the SR is located immediately below the membrane containing DHPRs. Conformational coupling between these two channels allows direct, bidirectional communication between the two separate membrane systems. The sensing of changes in surface membrane voltage by DHPR induces gating of RyR and results in calcium release from the sarcoplasmic reticulum during muscle activation. The two images are published in Block, B., Leung, A., Campbell, K.P., and Franzini-Armstrong, C. (1988). Structural evidence for direct interaction between the molecular components of the transverse tubules/sarcoplasmic reticulum junction in skeletal muscle. J. Cell Biol. 107, 2587-2600; and in Protasi, F., Franzini-Armstrong, C., and Flucher, B. (1997). Coordinated incorporation of skeletal muscle dihydropyridine receptors and ryanodine receptors in peripheral couplings of BC3H1 cells. J. Cell Biol. 137, 859-870. Clara Franzini-Armstrong