scholarly journals THE SARCOPLASMIC RETICULUM, THE T SYSTEM, AND THE MOTOR TERMINALS OF SLOW AND TWITCH MUSCLE FIBERS IN THE GARTER SNAKE

1965 ◽  
Vol 26 (2) ◽  
pp. 467-476 ◽  
Author(s):  
Arthur Hess
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Muscle Fibers ◽  
Postsynaptic Membrane ◽  
Slow Muscle ◽  
Garter Snake ◽  
Transverse Tubular System ◽  
Physiological Reaction ◽  
Slow Fiber ◽  
Tubular System ◽  
T System

Twitch and slow muscle fibers, identified morphologically in the garter snake, have been examined in the electron microscope. The transverse tubular system and the sarcoplasmic reticulum are separate entities distinct from each other. In twitch fibers, the tubular system and the dilated sacs of the sarcoplasmic reticulum form triads at the level of junction of A and I bands. In the slow fibers, the sarcoplasmic reticulum is severely depleted in amount and the transverse tubular system is completely absent. The junctional folds of the postsynaptic membrane of the muscle fiber under an "en grappe" ending of a slow fiber are not so frequent or regular in occurrence or so wide or so long as under the "en plaque" ending of a twitch fiber. Some physiological implications of these differences in fine structure of twitch and slow fibers are discussed. The absence of the transverse tubular system and reduction in amount of sarcoplasmic reticulum, along with the consequent disposition of the fibrils, the occurrence of multiple nerve terminals, and the degree of complexity of the post junctional folds of the sarcolemma appear to be the morphological basis for the physiological reaction of slow muscle fibers.

scholarly journals CORRELATED MORPHOLOGICAL AND PHYSIOLOGICAL STUDIES ON ISOLATED SINGLE MUSCLE FIBERS

1968 ◽  
Vol 38 (1) ◽  
pp. 115-129 ◽  
Author(s):  
Philip W. Brandt ◽  
John P. Reuben ◽  
Harry Grundfest
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Current Flow ◽  
Muscle Fibers ◽  
Single Muscle ◽  
Unit Membrane ◽  
Membrane Phase ◽  
Transverse Tubular System ◽  
Contraction Coupling ◽  
Cytoplasmic Material ◽  
Tubular System

Living muscle fibers of crayfish become dark during efflux of Cl-. This change in appearance is correlated with occurrence of vacuolation in the fixed fibers. The vacuoles begin at and are mainly confined to the terminals of the transverse tubular system (TTS) which are in diadic contact with the sarcoplasmic reticulum (SR). In electron micrographs swellings more than 1 µ in diameter may be seen connected to the sarcolemma or sarcolemmal invaginations by relatively unswollen tubules about 300–500 A wide. Darkening of the living fibers can be reversed by causing an influx of Cl-. Vacuoles are then absent in the fixed preparations. These findings accord with the conclusion that the membrane of the TTS is anion permselective. Localization of the selectivity to the membrane of the terminals of the TTS strengthens the hypothesis that a channeling of current flow is responsible for initiation of excitation-contraction coupling. During the swelling, and upon its reversal, the area of the membrane of the terminals must change reversibly by about two to four orders of magnitude. The absence of changes in the dimensions of the unit membrane indicates that the expansion of the membrane and its subsequent shrinkage involve reversible incorporation of cytoplasmic material into the membrane phase.

Transverse tubular system depolarization reduces tetanic force in rat skeletal muscle fibers by impairing action potential repriming

2007 ◽  
Vol 292 (6) ◽  
pp. C2112-C2121 ◽  
Author(s):  
T. L. Dutka ◽  
G. D. Lamb
Keyword(s):  
Muscle Fibers ◽  
Force Output ◽  
Tetanic Force ◽  
Internal Solution ◽  
Transverse Tubular System ◽  
Tubular System ◽  
Fast Twitch Muscle ◽  
Fast Twitch ◽  
Pulse Stimulation ◽  
T System

When muscle fibers are repeatedly stimulated, they may become depolarized and force output decline. Excitation of the transverse tubular system (T-system) is critical for activation, but its role in muscle fatigue is poorly understood. Here, mechanically skinned fibers from rat fast-twitch muscle were used, because the sarcolemma is absent but the T-system retains normal excitability and its properties can be studied in isolation. The T-system membrane was fully polarized by bathing the skinned fiber in an internal solution with 126 mM K+ (control solution) or set at partially depolarized levels (approximately −63 and −58 mV) in solutions with 66 or 55 mM K+, respectively, and action potentials (APs) were triggered in the sealed T-system by field stimulation. Prolonged depolarization of the T-system reduced tetanic force proportionately more than twitch force, with greater effect at higher stimulation frequency (responses at 20 and 100 Hz reduced to 71 and 62% in 66 mM K+ and to 54 and 35% in 55 mM K+, respectively). Double-pulse stimulation showed that depolarization increased the repriming period (estimated minimum time before a second AP can be produced) from ∼4 ms to ∼7.5 and 15 ms in the 66 and 55 mM K+ solutions, respectively. These results demonstrate that T-system depolarization reduces tetanic force by impairing AP repriming, rather than by preventing AP generation per se or by inactivating the T-system voltage sensors. The findings also explain why it is advantageous to reduce the rate of motoneuron stimulation to muscles during repeated or prolonged periods of activity.

scholarly journals THE SARCOPLASMIC RETICULUM AND ITS ASSOCIATION WITH THE T SYSTEM IN AN INSECT

1967 ◽  
Vol 32 (3) ◽  
pp. 535-545 ◽  
Author(s):  
Martin Hagopian ◽  
David Spiro
Keyword(s):  
Fine Structure ◽  
Sarcoplasmic Reticulum ◽  
Cell Surface ◽  
Osmium Tetroxide ◽  
Surface Membrane ◽  
Transverse Tubular System ◽  
Leucophaea Maderae ◽  
Tubular System ◽  
Femoral Muscle ◽  
T System

The fine structure of the sarcoplasmic reticulum and the transverse tubular system of the femoral muscle of the cockroach, Leucophaea maderae, was studied after prefixation in glutaraldehyde, postfixation in osmium tetroxide, and embedding in Epon. The sarcoplasmic reticulum in this muscle reveals features not previously reported. The sarcoplasmic reticulum is abundant, consisting mainly of a fenestrated envelope which surrounds each myofibril at all levels in the sarcomere. This sarcoplasmic reticulum envelope is continuous transversally as well as longitudinally along the myofibrils. Dyadic junctions are formed by a single T system element which contacts the unfenestrated sarcoplasmic reticulum of adjacent myofibrils in an alternating manner at the ends of the A band. At the dyads, regularly spaced thickenings of the sarcoplasmic reticulum membranes bordering the dyadic spaces are noted. These thickenings, however, do not contact the T tubule membrane. Typical dyadic contacts also are seen between the cell surface membrane and sarcoplasmic reticulum. Z line-like material is seen in contact with the membranes of the cell surface and longitudinal branches of the T systems.

scholarly journals Evidence for Anion-Permselective Membrane in Crayfish Muscle Fibers and Its Possible Role in Excitation-Contraction Coupling

1963 ◽  
Vol 47 (1) ◽  
pp. 189-214 ◽  
Author(s):  
Lucien Girardier ◽  
John P. Reuben ◽  
Philip W. Brandt ◽  
Harry Grundfest
Keyword(s):  
Muscle Fibers ◽  
Current Loop ◽  
Excitation Contraction Coupling ◽  
Transverse Tubular System ◽  
Contraction Coupling ◽  
Permselective Membrane ◽  
Tubular System ◽  
Inward Currents ◽  
A Current ◽  
T System

Under certain conditions only, isolated crayfish skeletal muscle fibers change in appearance, becoming grainy, darkening, and seemingly losing their striations. These changes result from development of large vesicles on both sides of the Z-line. The longitudinal sarcoplasmic reticulum remains unaffected. The vesicles are due to swelling of a transverse tubular system (TTS) which is presumably homologous with the T-system tubules of other muscle fibers. The vesiculations occur during efflux of water or on reducing external K or Cl, but only when KCl can leave the fiber. They never result from osmotic, ionic, or electrical changes when KCl cannot leave. Inward currents, applied through a KCl-filled intracellular cathode, also cause the vesiculations. These are not produced when the cathode is filled with K-propionate, nor by outward or longitudinal currents. Thus the transverse tubules swell only when Cl leaves the cell. Accordingly, their membrane is largely or exclusively anion-permselective. These findings also indicate that the TTS forms part of a current loop, connecting with the exterior of the fiber probably through radial tubules (RT) possessing membrane of low conductivity. Thus, part of the current flowing inward across the sarcolemma during activity can return to the exterior through the membrane of the TTS. The structure and properties of the latter offer the possibility for an efficient electrical mechanism to initiate excitation-contraction coupling.

Structure and innervation of the swim bladder musculature in the weakfish, Cynoscion regalis (Teleostei: Sciaenidae)

1982 ◽  
Vol 60 (8) ◽  
pp. 1955-1967 ◽  
Author(s):  
R. Dana Ono ◽  
Stuart G. Poss
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Muscle Fiber ◽  
Muscle Fibers ◽  
Postsynaptic Membrane ◽  
Motor Endplate ◽  
Central Core ◽  
Swim Bladder ◽  
Motor Endplates ◽  
Cynoscion Regalis

The striated swim bladder muscles of the weakfish Cynoscion regalis are deep red in color but cannot be classified histologically as having typical red fibers. The muscle fibers are homogeneous and average 29.6 ± 5.3 μm in diameter, one-fifth the diameter of the adjacent hypaxialis fibers. Each muscle fiber contains thin, ribbonlike myofibrils which are radially arranged around a central core of mitochondria, glycogen, and sarcoplasmic reticulum. Myofibrils are extremely regular in pattern. Triads occur at the Z line. Numerous mitochondria and muscle nuclei are located at the periphery of each muscle fiber. The muscle fibers are multiply innervated with motor endplates distributed along their entire lengths. Well-developed folding of the postsynaptic membrane, not previously reported in fishes, is present at the motor endplate.

scholarly journals THE STRUCTURE OF INTERSEGMENTAL MUSCLE FIBERS IN AN INSECT, PERIPLANETA AMERICANA L

1966 ◽  
Vol 29 (3) ◽  
pp. 449-459 ◽  
Author(s):  
David S. Smith
Keyword(s):  
Periplaneta Americana ◽  
Flight Muscle ◽  
Muscle Fibers ◽  
Structural Features ◽  
Mitochondrial Content ◽  
Thin Filaments ◽  
Transverse Tubular System ◽  
Thick Filaments ◽  
Tubular System ◽  
Contraction And Relaxation

The organization of intersegmental muscle fibers associated with the dorsal abdominal sclerites of the cockroach is described. These fibers correspond closely, in the disposition and derivation of the membranes of the transverse tubular system and sarcoplasmic reticulum cisternae, with insect synchronous flight muscle fibers, but differ markedly from these in their fibrillar architecture and mitochondrial content. The mitochondria are small and generally aligned alongside the prominent I bands of the sarcomere, and, in the best-oriented profiles of the A bands, thick filaments are associated with orbitals of twelve thin filaments, a configuration that has also been observed in striated fibers of insect visceral muscle. These structural features of insect muscles are compared and discussed in terms of possible variations in the control of contraction and relaxation, and in the nature of their mechanical role.

Sign in / Sign up

Export Citation Format

Share Document