Myosin heavy chain isoform expression and Ca2 +-stimulated ATPase activity in single fibres of toad rectus abdominis muscle

• Published in: Journal of muscle research and cell motility 2002-01, Vol.23 (2), p.147-156
• Main Authors: Nguyen, Long Thanh, Stephenson, Gabriela M M
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatase; Alanine; Animals; Bufo marinus; Ca(2+) Mg(2+)-ATPase - metabolism; Calcium; Calcium - metabolism; Calcium - pharmacology; Feedback inhibition; Hybrids; Isoforms; Muscular system; Myosin; Myosin Heavy Chains - biosynthesis; Nerve Fibers - drug effects; Nerve Fibers - enzymology; Protein Isoforms - biosynthesis; Proteins; Rectus Abdominis - drug effects; Rectus Abdominis - enzymology; Sarcoplasmic reticulum; Skeletal muscle; Spectrophotometry
• ISSN: 0142-4319; 1573-2657
• DOI: 10.1023/A:1020266422201

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.