Myosin heavy chain isoform expression and Ca2 +-stimulated ATPase activity in single fibres of toad rectus abdominis muscle
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Updated: Jul 29, 2026

In Vivo Calcium Imaging in C. elegans Body Wall Muscles
Published on: October 20, 2019
Long Thanh Nguyen1, Gabriela M M Stephenson
1Muscle Cell Biochemistry Laboratory, School of Life Sciences and Technology, Victoria University, Melbourne, Australia.
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.
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