title: Myosin heavy chain isoform expression and Ca2 +-stimulated ATPase activity in single fibres of toad rectus abdominis muscle.
abstract: Segments of single fibres from the rectus abdominis (RA) muscles of adult and juvenile cane toads (Bufo marinus) were examined for myosin heavy chain (mHC) isoform expression and Ca2+-stimulated MgATPase activity. mHC isoform analyses were carried out using the recently developed alanine-SDS-PAGE method, which separates one tonic (BmHCT) and three twitch (BmHC1, BmHC2, BmHC3) mHC isoforms in toad skeletal muscle. Ca2+-stimulated MgATPase activity was measured by spectrophotometric determination of Pi, under conditions in which the ATPase associated with the sarcoplasmic reticulum (SR ATPase) was suppressed by feedback inhibition. The mHC-based fibre types identified in this study include three pure twitch fibre types (t1, t2 and t3), expressing BmHC1, BmHC2 or BmHC3 respectively, and seven hybrid fibre types co-expressing a combination of two or three twitch and tonic or twitch and twitch mHC isoforms. The fibre populations dissected from juvenile and adult toad muscles contained 49.4% (juvenile) and 73.7% (adult) mHC hybrids. The average values for Ca2+-stimulated MgATPase in pure twitch fibres and in fibres expressing predominantly (> or = 95%) the tonic mHC isoform (Tp fibres) differed significantly (P < 0.05) from each other and decreased in the order t1 > t2 > t3 > Tp. We conclude that (i) in RA muscles of both juvenile and adult cane toads there is a large proportion of mHC hybrids, some of which co-express twitch and tonic mHC isoforms and (ii) ATPase activities associated with the four mHC isoforms expressed in toad skeletal muscles decrease in the order BmHC1 > BmHC2 > BmHC3 > BmHCT.
authors.affiliation: Muscle Cell Biochemistry Laboratory, School of Life Sciences and Technology, Victoria University, Melbourne, Australia.
authors.forename: Long Thanh
authors.initials: LT
authors.lastname: Nguyen
authors.forename: Gabriela M M
authors.initials: GM
authors.lastname: Stephenson
mesh_terms: D000818:Animals; D002024:Bufo marinus; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D009412:Nerve Fibers / Q000187:drug effects / Q000201:enzymology*; D020033:Protein Isoforms / Q000096:biosynthesis; D017568:Rectus Abdominis / Q000187:drug effects / Q000201:enzymology*
chemical_list: D020033:Protein Isoforms; D017301:Ca(2+) Mg(2+)-ATPase; D018995:Myosin Heavy Chains; D002118:Calcium