Ultrastructural and biochemical analysis of the sarcoplasmic reticulum from crayfish fast and slow striated muscles

Abstract

AbstractUltrastructural and biochemical properties were compared between two types of the sarcoplasmic reticulum (SR), one from the deep extensor abdominal muscle medialis (fast muscle) and the other from the flexor muscle of carpopodite in meropodite (slow muscle) of crayfish Procambarus clarkii. Electron microscopic observations revealed that terminal cisternae of the SR of crayfish fast muscle was well‐developed and contained feet‐like structures. In transverse sections, the SR of slow muscle was tubule‐like in shape and the terminal cisternae of the SR occupied smaller area than those of the fast muscle SR. The fragmented SR obtained from the homogenized fast muscle was poorly separated by ultracentrifugation with a sucrose gradient (25–50%): both vesicles from light and heavy fractions contained terminal cisternae and were connected to transverse tubules via the feet‐like structures. In contrast, the slow muscle fragmented SR could be separated in to the light and heavy fractions, which contained elliptical vesicles and vesicles with the feet‐like structures, respectively. Sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis and subsequent 45Ca ligand overlay analyses revealed that a 105,000 ( =105 k) Da protein was the major protein in both SRs, which lacked Ca2+‐binding proteins corresponding to vertebrate calsequestrins. On the other hand, peptide‐mapping of the 105 kDa protein in SDS‐gels suggested no difference in the primary structure between fast and slow SR. Ca2+‐ATPase and Ca2+ uptake activities of the fast muscle SR at 20°C were 0.39 μmol Pi/min·mg and 0.57 μmol Ca/min·mg, respectively, which were clearly higher than those of the slow muscle SR, 0.27 μmol Pi/min·mg, and 0.37 μmol Ca/min·mg, respectively.These results suggest that the SR of crayfish fast and slow muscles were morphologically and enzymatically different, which might partly cause differences in the contractile properties of fast and slow muscles. © 1993Wiley‐Liss, Inc.