Faculty Opinions recommendation of The Ca(2+) influx through the mammalian skeletal muscle dihydropyridine receptor is irrelevant for muscle performance.

To find out whether the decrease in muscle performance of isolated mammalian skeletal muscle associated with the increase in temperature toward physiological levels is related to the increase in muscle superoxide (O2•−) production, O2•−released extracellularly by intact isolated rat and mouse extensor digitorum longus (EDL) muscles was measured at 22, 32, and 37°C in Krebs-Ringer solution, and tetanic force was measured in both preparations at 22 and 37°C under the same conditions. The rate of O2•−production increased marginally when the temperature was increased from 22 to 32°C, but increased fivefold when the temperature was increased from 22 to 37°C in both rat and mouse preparations. This increase was accompanied by a marked decrease in tetanic force after 30 min incubation at 37°C in both rat and mouse EDL muscles. Tetanic force remained largely depressed after return to 22°C for up to 120 min. The specific maximum Ca2+-activated force measured in mechanically skinned fibers after the temperature treatment was markedly depressed in mouse fibers but was not significantly depressed in rat muscle fibers. The resting membrane and intracellular action potentials were, however, significantly affected by the temperature treatment in the rat fibers. The effects of the temperature treatment on tetanic force, maximum Ca2+-activated force, and membrane potential were largely prevented by 1 mM Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a membrane-permeable superoxide dismutase mimetic, indicating that the increased O2•−production at physiological temperatures is largely responsible for the observed depression in tetanic force at 37°C by affecting the contractile apparatus and plasma membrane.

Download Full-text

Calcium Ion in Skeletal Muscle: Its Crucial Role for Muscle Function, Plasticity, and Disease

Physiological Reviews ◽

10.1152/physrev.2000.80.3.1215 ◽

2000 ◽

Vol 80 (3) ◽

pp. 1215-1265 ◽

Cited By ~ 544

Author(s):

Martin W. Berchtold ◽

Heinrich Brinkmeier ◽

Markus Müntener

Keyword(s):

Skeletal Muscle ◽

Sarcoplasmic Reticulum ◽

Binding Proteins ◽

Muscle Fibers ◽

Protein Isoforms ◽

Muscle Performance ◽

High Plasticity ◽

Mammalian Skeletal Muscle ◽

Variable Expression ◽

Functional Features

Mammalian skeletal muscle shows an enormous variability in its functional features such as rate of force production, resistance to fatigue, and energy metabolism, with a wide spectrum from slow aerobic to fast anaerobic physiology. In addition, skeletal muscle exhibits high plasticity that is based on the potential of the muscle fibers to undergo changes of their cytoarchitecture and composition of specific muscle protein isoforms. Adaptive changes of the muscle fibers occur in response to a variety of stimuli such as, e.g., growth and differentition factors, hormones, nerve signals, or exercise. Additionally, the muscle fibers are arranged in compartments that often function as largely independent muscular subunits. All muscle fibers use Ca2+ as their main regulatory and signaling molecule. Therefore, contractile properties of muscle fibers are dependent on the variable expression of proteins involved in Ca2+ signaling and handling. Molecular diversity of the main proteins in the Ca2+ signaling apparatus (the calcium cycle) largely determines the contraction and relaxation properties of a muscle fiber. The Ca2+ signaling apparatus includes 1) the ryanodine receptor that is the sarcoplasmic reticulum Ca2+ release channel, 2) the troponin protein complex that mediates the Ca2+ effect to the myofibrillar structures leading to contraction, 3) the Ca2+pump responsible for Ca2+ reuptake into the sarcoplasmic reticulum, and 4) calsequestrin, the Ca2+storage protein in the sarcoplasmic reticulum. In addition, a multitude of Ca2+-binding proteins is present in muscle tissue including parvalbumin, calmodulin, S100 proteins, annexins, sorcin, myosin light chains, β-actinin, calcineurin, and calpain. These Ca2+-binding proteins may either exert an important role in Ca2+-triggered muscle contraction under certain conditions or modulate other muscle activities such as protein metabolism, differentiation, and growth. Recently, several Ca2+signaling and handling molecules have been shown to be altered in muscle diseases. Functional alterations of Ca2+ handling seem to be responsible for the pathophysiological conditions seen in dystrophinopathies, Brody's disease, and malignant hyperthermia. These also underline the importance of the affected molecules for correct muscle performance.

Download Full-text