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The sarcoplasmic concentrations of phosphorus metabolites and pH (pHin) were measured in the anterior byssus retractor muscle (ABRM) ofMytilus edulis by31P nuclear magnetic resonance spectroscopy. During an active contraction induced by 10−3 m acetylcholine, the concentration of arginine phosphate ([Arg-P]in) decreased from the resting value of 7.47±0.26 (mean±se,n=8) to 6.67±0.29 (n=6) μmol g−1, and that of inorganic phosphate (Pi) consistently increased from 0.84±0.06 (n=7) to 1.61±0.12 (n=5) μmol g−1. In the ‘catch’ state following the active contraction, these concentrations were close to their resting levels, indicating that the catch is an inactive state. 5-hydroxytryptamine caused a rapid relaxation of the catch, which was associated with a slight decrease in [Arg-P]in and an increase in pHin by ca 0.2 units. The sarcoplasmic concentration of ATP (mean, 1.6μmol g−1) did not change throughout the contraction-relaxation cycle.

Dr. John Gergely passed away on July 26, 2013 after a long and distinguished career. His publications spanned 67 years. He founded the Department of Muscle Research in the Retina Foundation (which later became the Boston Biomedical Research Institute) and served as director for 34 years. Dr. Gergely served on the editorial boards of ten scientific journals. He was elected as a Fellow of both the Biophysical Society and the American Association for the Advancement of Science. Dr. Gergely made major contributions concerning muscle protein structure and function. He was best known for his work on the troponin complex. The insights of John and his associates have provided the foundation for our understanding of calcium regulation in skeletal and cardiac muscle.

This review proposes a link between the hypertrophic (HCM) and restrictive cardiomyopathies caused by mutations in several sarcomeric thin filament proteins, and the open state of the three-state muscle regulation theory. The three characteristics of various muscle systems reconstituted from HCM mutated proteins (increased Ca2+-sensitivity, increased basal activity in the absence of Ca2+, and decreased cooperativity) can be explained by the contribution of a myosin-induced open state (M − ), which elevates the basal activity and competes with the normal Ca2+-activated pathway. A model based on the three-state theory of regulation, shows how a change in the closed/blocked equilibrium caused by a mutation that weakens the binding of troponin I to tropomyosin-actin can produce the characteristics of HCM. This review also shows that in the M − state, Ca2+ can shift the closed–open equilibrium of the N-terminal hydrophobic region of troponin C without affecting activity.

The porcine perinatal myosin heavy chain (MyHC) is a major isoform in foetal skeletal muscles. We report here on its cDNA and genomic isolation, molecular characterisation and expression. Exon 2 and the first 4 bases of exon 3 of the perinatal MyHC gene, both part of the 5′-end untranslated region, showed differential splicing. About 2% of all perinatal MyHC transcripts of a 50-day-old foetus were without exon 2 and about half were without the 4 bases at the 5′-end of exon 3. Perinatal MyHC mRNA was expressed in all hind limb muscles of a 45-day-old foetus along with the slow and embryonic MyHC isoforms in the same fibres. Unlike other sarcomeric MyHCs reported to date, the porcine perinatal promoter is clustered with repeat elements (4 SINEs and 1 microsatellite) and is without a consensus TATA box at the predicted site upstream of exon 1. Nonetheless, in reporter gene transfections, its promoter was found to be highly muscle-specific. The absence of a TATA box may point to a fundamental difference in the regulatory function between the perinatal and adult MyHC isoforms.

This article lays out the determinants of maximal O2 consumption (VO2max) achieved during high intensity endurance exercise. It is not a traditional topical review but rather an educational essay that intertwines chance observations made during an unrelated research project with a subsequent program of stepwise thought, analysis and experimentation to reveal how O2 is delivered to and used by the mitochondria. The centerpiece is the recognition that O2 is delivered by an inter-dependent system of transport components functioning as a “bucket brigade”, made up of the lungs, heart, blood and circulation, and the muscles themselves, each of which affects O2 transport by similar amounts as they change. There is thus no single “limiting factor” to VO2max. Moreover, each component is shown to quantitatively affect the performance of the others. Mitochondrial respiration is integrated into the O2 transport system analysis to reveal its separate contribution to VO2max, and to show that mitochondrial PO2 at VO2max must be extremely low. Clinical application of the O2 transport systems analysis is described to separate central cardiopulmonary from peripheral tissue contributions to exercise limitation, illustrated by a study of patients with COPD. Finally, a short discussion of why muscles operating maximally must endure an almost anoxic state is offered. The hope is that in sum, both the increased understanding of O2 transport and the scientific approach to achieving that understanding described in the review can serve as a model for solving other complex problems going forward.

This study investigated the contractile properties of single skeletal muscle fibres from the Vastus lateralis (VL) of two male adult chachma baboons (Papio ursinus) and compared it to that from five male human cyclists. Species comparisons are observational and statistical analyses were not performed due to the low sample size. The histological analyses revealed that the baboon muscles contained more type II fibres than their human counterparts. Cross-sectional areas of type I and type II fibres from human VL were similar in size, whereas baboon type I and type II fibres appeared smaller and larger compared to humans, respectively. On average, type II fibres from baboons and type IIAX fibres from humans produced the highest specific force (88 ± 41 and 155 ± 4 kN/m2, respectively), compared to 57 ± 27 and 68 ± 5 kN/m2 for baboon and human type I fibres. Maximum shortening velocity appeared highest in human type IIAX fibres, but fairly similar between human and baboon type I and II fibres. Baboon and human type I (2.2 ± 0.4 vs. 1.5 ± 0.5 kN/m2 Fl/s) and type II (6.0 ± 2.8 vs. 7.7 ± 1.0 kN/m2 Fl/s) fibres appeared similar in maximum power output. From these observations, it seems that baboon and human muscle fibre contractile properties appear similar to one another, and that fibre type composition itself may play a determining role in muscle strength between these two species.

N,N,N′,N′-tetrakis(2-pyridylmethyl)-ethilenediamine (TPEN) is a membrane permeable heavy metal chelator that has been used to study intracellular calcium homeostasis but its exact mode of action is still unresolved. Here we examine the effects of TPEN on the Ca2+ release from and the Ca2+ uptake into the sarcoplasmic reticulum (SR) of cultured C2C12 skeletal muscle cells. Low concentrations (50 μM) of the drug evoked Ca2+ transients in ∼60% of C2C12 myotubes, while at high concentrations (500 μM) it significantly reduced the size of both depolarization-and caffeine-induced Ca2+ transients, decreased the rate constant of decay and the calculated pump activity but failed to induce Ca2+ transients. Experiments at low extracellular [Ca2+] revealed that it is the total rather than free TPEN concentration that is responsible for the observed effects. TPEN does not modify Ca2+ release by Zn2+ chelation, as evidenced by the unaltered effect seen after the removal of Zn2+ from the extracellular space of the cells by chelating with EDPA. These findings provide experimental evidence that TPEN directly modifies both the release of Ca2+ from the SR and its removal from the myoplasm.

Stretchin-klp is a newly described protein in Drosophila indirect flight muscles (IFM) that migrates on SDS gels as two distinct components of approximately 225 and 231 kD. Although the larger isoform is IFM specific, the smaller stretchin-klp isoform is expressed not only in IFM, but also in wild-type tissues of the adult head, abdomen and thorax from which the IFM has been removed. It is not detected, however, in jump or leg muscles. Probes derived from a cDNA encoding part of stretchin-klp hybridize with a 6.7 kb mRNA. Stretchin-klp is one of several putative products of the Stretchin-Myosin light chain kinase gene and is predicted to have multiple immunoglobulin domains arranged in tandem pairs separated by variable length spacers. Polyclonal antibodies directed against the expressed peptide of the stretchin-klp cDNA label the IFM myofibril A-band, though not its central and lateral regions. Analyses of IFM mutants indicate that the larger stretchin-klp isoform is myosin dependent. Although the normal adult myosin filament or the ‘headless’ myosin rod is sufficient for accumulation of both the large and small stretchin-klp isoforms, loss of myosin, or substitution of the adult rod with an embryonic one in IFM prevents the larger isoform from being formed or stabilized. During development stretchin-klp is first detected at pupal stage p8, when myofibrils are being constructed. These studies suggest that this newly identified protein is a major component of the Drosophila IFM thick filament.