scholarly journals COMPARISON OF GLYCEROL TREATMENT IN FROG SKELETAL MUSCLE AND MAMMALIAN HEART

1971 ◽  
Vol 50 (2) ◽  
pp. 288-299 ◽  
Author(s):  
G. Niemeyer ◽  
W. G. Forssmann
Keyword(s):  
Skeletal Muscle ◽  
Heart Muscle ◽  
Frog Skeletal Muscle ◽  
Mammalian Heart ◽  
Glycerol Treatment ◽  
Before And After ◽  
Tracer Methods ◽  
Mammalian Heart Muscle ◽  
T System

Frog skeletal muscle and mammalian heart muscle were studied in vitro before and after glycerol treatment. Loss of contractility, changes in the action potential and disruption of the T system were observed in skeletal muscle cells. In mammalian heart muscle the T system was not disrupted with hypertonic glycerol treatment, and no significant electrophysiological changes were observed. The continuity between the T system and the extracellular space was investigated by diffusion tracer methods. Decrease of contractility during the hypertonic phase in the glycerol treatment was found to depend on tonicity. The results of this study clearly show that not only are there differences in morphology between skeletal and cardiac muscle, but there are also differences in the resistance to osmotic changes.

The Croonian Lecture, 1977 - Stretch activation of muscle: function and mechanism

1978 ◽  
Vol 201 (1143) ◽  
pp. 107-130 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Heart Muscle ◽  
Flight Muscle ◽  
Mechanical Activity ◽  
Myosin Filament ◽  
Active Tension ◽  
Stretch Activation ◽  
Mammalian Heart ◽  
Mammalian Heart Muscle ◽  
Vertebrate Skeletal Muscle

Current theories about the mechanism of muscular contraction suppose that the level of enzymic and contractile activity is controlled by the intracellular concentration of calcium ions, the degree of overlap between the myosin and actin filaments and the rate of relative sliding of the filaments. It is now known that in most or all muscles there is a further direct influence of mechanical conditions, usually called stretch activation; changes of length lead to a delayed change of active tension. The effect is large and functionally significant in insect fibrillar flight muscle and in mammalian heart muscle; it is present, but small, in vertebrate skeletal muscle, which probably accounts for its late discovery. In insect fibrillar flight muscle, the delayed tension is responsible for the rhythmic mechanical activity during flight. In mammalian heart muscle it may play a rôle in Starling’s Law. In insect fibrillar muscle, extension produces a maintained increase in actomyosin ATPase and active tension; in vertebrate skeletal muscle, stretch activation is a transient phenomenon. Mammalian heart muscle shows greater maintenance of stretch activation than skeletal muscle; the duration of higher ATPase activity has not yet been determined. The effective mechanical parameter is not overall strain but is probably the strain on an internal structure related to overall stress. Various lines of evidence point to the myosin filament as the location of the sensor. A considerable degree of molecular synchronization occurs during natural insect flight.

scholarly journals PPADS does not block contraction-induced prostaglandin E2 synthesis in cat skeletal muscle

2008 ◽  
Vol 295 (5) ◽  
pp. H2043-H2045 ◽  
Author(s):  
Jennifer L. McCord ◽  
Shawn G. Hayes ◽  
Marc P. Kaufman
Keyword(s):  
Skeletal Muscle ◽  
Pyridoxal Phosphate ◽  
Pressor Response ◽  
Triceps Surae ◽  
Prostaglandin E ◽  
Exercise Pressor Reflex ◽  
Before And After ◽  
Pressor Reflex ◽  
Response To Exercise

Pyridoxal-phosphate-6-azophenyl-2′-4-disulfonate (PPADS), a purinergic 2 (P2) receptor antagonist, has been shown to attenuate the exercise pressor reflex in cats. In vitro, however, PPADS has been shown to block the production of prostaglandins, some of which play a role in evoking the exercise pressor reflex. Thus the possibility exists that PPADS blocks the exercise pressor reflex through a reduction in prostaglandin synthesis rather than through the blockade of P2 receptors. Using microdialysis, we collected interstitial fluid from skeletal muscle to determine prostaglandin E2 (PGE2) concentrations during the intermittent contraction of the triceps surae muscle before and after a popliteal arterial injection of PPADS (10 mg/kg). We found that the PGE2 concentration increased in response to the intermittent contraction before and after the injection of PPADS (both, P < 0.05). PPADS reduced the pressor response to exercise ( P < 0.05) but had no effect on the magnitude of PGE2 production during contraction ( P = 0.48). These experiments demonstrate that PPADS does not block the exercise pressor reflex through a reduction in PGE2 synthesis. We suggest that PGE2 and P2 receptors play independent roles in stimulating the exercise pressor reflex.

scholarly journals DIFFERENTIATION OF THE SARCOPLASMIC RETICULUM AND T SYSTEM IN DEVELOPING CHICK SKELETAL MUSCLE IN VITRO

1967 ◽  
Vol 35 (2) ◽  
pp. 405-420 ◽  
Author(s):  
Elizabeth B. Ezerman ◽  
Harunori Ishikawa
Keyword(s):  
Skeletal Muscle ◽  
Electron Microscope ◽  
Sarcoplasmic Reticulum ◽  
Osmium Tetroxide ◽  
Muscle Cells ◽  
Simultaneous Occurrence ◽  
Chick Embryos ◽  
Developing Muscle ◽  
T System

The electron microscope was used to investigate the first 10 days of differentiation of the SR and the T system in skeletal muscle cultured from the breast muscle of 11-day chick embryos. The T-system tubules could be clearly distinguished from the SR in developing muscle cells fixed with glutaraldehyde and osmium tetroxide. Ferritin diffusion confirmed this finding: the ferritin particles were found only in the tubules identified as T system. The proliferation of both membranous systems seemed to start almost simultaneously at the earliest myotube stage. Observations suggested that the new SR membranes developed from the rough-surfaced ER as tubular projections. The SR tubules connected with one another to form a network around the myofibril. The T-system tubules were formed by invagination of the sarcolemma. The early extension of the T system by branching and budding was seen only in subsarcolemmal regions. Subsequently the T-system tubules could be seen deep within the muscle cells. Immediately after invaginating, the T-system tubule formed, along its course, specialized connections with the SR or ER: triadic structures showing various degrees of differentiation. The simultaneous occurrence of myofibril formation and membrane proliferation is considered to be important in understanding the coordinated events resulting in the differentiated myotube.

scholarly journals Simultaneous measurement of Ca2+ in muscle with Ca electrodes and aequorin. Diffusible cytoplasmic constituent reduces Ca(2+)-independent luminescence of aequorin.

1991 ◽  
Vol 98 (6) ◽  
pp. 1141-1160 ◽  
Author(s):  
L A Blatter ◽  
J R Blinks
Keyword(s):  
Skeletal Muscle ◽  
Simultaneous Measurement ◽  
Light Emission ◽  
Ringer Solution ◽  
Light Signal ◽  
Frog Skeletal Muscle ◽  
Stable Level ◽  
Total Absence ◽  
Normal Ringer

Estimates of cytoplasmic Ca2+ concentration ([Ca2+]i) were made essentially simultaneously in the same intact frog skeletal muscle fibers with aequorin and with Ca-selective microelectrodes. In healthy fibers under truly resting conditions [Ca2+]i was too low to be measured reliably with either technique. The calibration curves for both indicators were essentially flat in this range of [Ca2+], and the aequorin light signal was uniformly below the level to be expected in the total absence of Ca2+. When [Ca2+]i had been raised to a stable level below the threshold for contracture by increasing [K+]o to 12.5 mM, [Ca2+]i was 38 nM according to aequorin and 59 nM according to the Ca-selective microelectrodes. These values are not significantly different. Our estimates of [Ca2+]i are lower than most others obtained with microelectrodes, probably because the presence of aequorin in the cells allowed us to detect damaging microelectrode impalements that otherwise we would have had no reason to reject. The observation that the light emission from aequorin-injected fibers in normal Ringer solution was below the level expected from the Ca(2+)-independent luminescence of aequorin in vitro was investigated further, with the conclusion that the myoplasm contains a diffusible macromolecule (between 10 and 30 kD) that interacts with aequorin to reduce light emission in the absence of Ca2+.

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