The transverse tubular (T) system of rat cardiac muscle fibers as demonstrated by tannic acid mordanting

1978 ◽  
Vol 56 (9) ◽  
pp. 1906-1916 ◽  
Author(s):  
T. S. Leeson
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Tannic Acid ◽  
Extracellular Space ◽  
Inverse Relationship ◽  
Muscle Fibres ◽  
Fiber Size ◽  
T Tubules ◽  
Cardiac Muscle Fibers ◽  
T System

T-tubules and subsarcolemmal caveolae in rat cardiac muscle fibres have been studied using the tannic acid mordanting technique. While T-tubules form an extensive and relatively regular meshwork with triads at Z-lines in ventricular fibers, in atrial fibers the tubules are often absent, or very sparse and with an irregular distribution. There appears to be a relation to fiber size, the meshwork being more extensive in fibers of larger diameter, and an inverse relationship to the number of couplings found between sarcoplasmic reticulum and plasmalemma. In larger atrial fibers, while the T-tubule meshwork was extensive, it did not show the regularity of distribution found in ventricular fibers. T-tubule continuity with the extracellular space was visualized clearly, both directly and indirectly via subsarcolemmal caveolae.

A transmission delay and the effect of temperature at the triadic junction of skeletal muscle

1986 ◽  
Vol 229 (1254) ◽  
pp. 97-110 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Effect Of Temperature ◽  
Muscle Fibres ◽  
Time Interval ◽  
Strong Temperature Dependence ◽  
Ca Channels ◽  
T Tubules ◽  
Skeletal Muscle Fibres ◽  
Terminal Cisternae

The coupling process at the triadic junctions in skeletal muscle fibres is characterized by a significant latency between the depolarization of the transverse tubular membrane and the release of Ca from the sarcoplasmic reticulum. This time interval, the triadic delay, is sufficiently long to allow for the participation of a chemical process. The strong temperature dependence of the triadic delay ( Q 10 near 2.7) suggests that a sequence of chemical steps may link the electical signal in the T-tubules to the opening of Ca channels in the terminal cisternae of the sarcoplasmic reticulum.

Calycophoran siphonophore muscle fibres without any sarcoplasmic reticulum but with tubular invaginations morphologically analogous to a T-system

1999 ◽  
Vol 79 (6) ◽  
pp. 1111-1116
Author(s):  
Q. Bone ◽  
C. Carré ◽  
I. Tsutsui ◽  
I. Inoue
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Action Potentials ◽  
Marine Invertebrates ◽  
Exchange Mechanism ◽  
Muscle Fibres ◽  
Previous Suggestion ◽  
Tubular System ◽  
Intracellular Ca ◽  
Morphological Equivalent ◽  
T System

Different marine invertebrates have different tubular or vesicular systems within their locomotor muscle fibres. The siphonophores Chelophyes, Abylopsis and Muggeia have invaginated tubules which are the morphological equivalent of the vertebrate invaginated tubular system, but lack a sarcoplasmic reticulum. In Chelophyes the previous suggestion that Ca2+ channels in the extensive invaginated tubule system allow ingress of Ca2+ is shown to be incorrect. Contraction of the swimming muscles in Chelophyes is not blocked by 20 μM ryanodine, nor is it induced by 10 mM caffeine, hence intracellular Ca2+ stores appear absent. Contraction is, however, maintained by replacement of the greater part of the usual external Na+ by Li+ or by or N-methyl-D-glucamine, although action potentials can still be evoked. Hence we conclude that following contraction, internal Ca2+ is reduced by a Na/Ca2+ exchange mechanism.

scholarly journals CARDIAC MUSCLE

1968 ◽  
Vol 36 (3) ◽  
pp. 497-526 ◽  
Author(s):  
Joachim R. Sommer ◽  
Edward A. Johnson
Keyword(s):  
Electron Microscopy ◽  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Cardiac Muscle ◽  
Extracellular Space ◽  
Light And Electron Microscopy ◽  
Rabbit Heart ◽  
Contraction Coupling ◽  
The Difference

With light and electron microscopy a comparison has been made of the morphology of ventricular (V) and Purkinje (P) fibers of the hearts of guinea pig, rabbit, cat, dog, goat, and sheep. The criteria, previously established for the rabbit heart, that V fibers are distinguished from P fibers by the respective presence and absence of transverse tubules is shown to be true for all animals studied. No evidence was found of a permanent connection between the sarcoplasmic reticulum and the extracellular space. The sarcoplasmic reticulum (SR) of V fibers formed couplings with the sarcolemma of a transverse tubule (interior coupling) and with the peripheral sarcolemma (peripheral coupling), whereas in P fibers the SR formed only peripheral couplings. The forms of the couplings were identical. The significance, with respect to excitation-contraction coupling, of the difference in the form of the couplings in cardiac versus skeletal muscle is discussed together with the electrophysiological implications of the differing geometries of bundles of P fibers from different animals.

Effects of rest duration and ryanodine on changes of extracellular [Ca] in cardiac muscle from rabbits

1987 ◽  
Vol 253 (3) ◽  
pp. C398-C407 ◽  
Author(s):  
K. T. MacLeod ◽  
D. M. Bers
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Extracellular Space ◽  
Ventricular Muscle ◽  
Rest Interval ◽  
Continuous Stimulation ◽  
Rabbit Ventricular Muscle ◽  
Interpretive Framework ◽  
Rest Intervals

Cumulative depletions of extracellular Ca were measured using double-barreled Ca-sensitive microelectrodes in the extracellular space of rabbit ventricular muscle. Depletions were produced by 1-Hz stimulation after rest intervals of 10 s to 10 min. With longer rest intervals, depletion size increased while the first postrest contraction decreased in a reciprocal manner. The depletions may represent refilling of sarcoplasmic reticulum (SR) Ca stores that have become partially depleted of Ca during the rest. Within this interpretive framework, the longer the rest interval the lower the SR Ca content, so the SR is then capable of taking up larger amounts of Ca. This may be related to the rest decay of tension of the first postrest beat, since this is thought to be SR dependent. Ryanodine (1 microM) increased the size of the depletions after short rest intervals (less than 2 min) but not after longer (greater than or equal to 2 min) intervals. Ryanodine also increased the rate of Ca loss from the cell on cessation of stimulation. This increased rate of Ca loss with ryanodine may deplete the SR of Ca such that more Ca can be taken up during subsequent stimulation than in untreated muscles. Thus cumulative depletions after short rest intervals are enhanced by ryanodine. When a Ca load was produced during 1) quiescence [by removal of extracellular Na (Nao)] or 2) continuous stimulation (in the presence of 3 microM acetylstrophanthidin), addition of ryanodine (5-10 microM) did not produce any apparent Ca loss. Caffeine (10 mM), added after ryanodine, induced contractures accompanied by Ca efflux, implying there was Ca in the SR after ryanodine exposure. The results of other investigators have suggested that ryanodine may inhibit cardiac SR Ca release. The present study suggests that ryanodine also enhances the loss of cellular (and probably SR) Ca on cessation of stimulation but not when applied during continuous stimulation or quiescence.

scholarly journals CARDIAC MUSCLE

1971 ◽  
Vol 49 (1) ◽  
pp. 50-65 ◽  
Author(s):  
Paul H. Jewett ◽  
J. R. Sommer ◽  
E. A. Johnson
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Muscle Fibers ◽  
Cardiac Cells ◽  
Transverse Tubules ◽  
Heart Rates ◽  
Intercalated Discs ◽  
Cardiac Muscle Fibers ◽  
Morphological Differences

Cardiac muscle fibers of the hummingbird and finch have no transverse tubules and are smaller in diameter than those of mammalian hearts. The fibers are connected by intercalated discs which are composed of desmosomes and f. adherentes; small nexuses are often interspersed. As in cardiac muscle of several other animals, the junctional SR of the couplings is highly structured in these two birds but, in addition, and after having lost sarcolemmal contact, the junctional SR continues beyond the coupling to extend deep into the interior of the cells and to form belts around the Z-I regions of the sarcomeres. This portion of the sarcoplasmic reticulum, which we have named "extended junctional SR," and which is so prominent and invariant a feature of cardiac cells of hummingbirds and finches, has not been observed in chicken cardiac cells. The morphological differences between these species of birds may be related to respective differences in heart rates characteristic for these birds.

scholarly journals Caffeine and micromolar Ca2+ concentrations can release Ca2+ from ryanodine-sensitive stores in crab and lobster striated muscle fibres

1996 ◽  
Vol 199 (11) ◽  
pp. 2419-2428 ◽  
Author(s):  
T Lea
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Striated Muscle ◽  
Abdominal Muscle ◽  
Isometric Tension ◽  
Muscle Fibres ◽  
Phasic Contraction ◽  
Crustacean Muscle ◽  
Time Integral ◽  
Variable Nature

Ca2+ release mechanisms were studied in striated muscle from the walking legs of crabs using isometric tension recordings from isolated myofibrillar bundles. Caffeine-induced phasic contractions had properties consistent with Ca2+ release from a sarcoplasmic store, which could be optimally loaded in the presence of ATP at pCa 6.4­6.1. Ryanodine (10 µmol l-1) abolished the caffeine-induced contractions and in solutions with low Ca2+ buffering (0.1 mmol l-1 EGTA) itself caused phasic contractions, indicative of Ca2+ release. Ca2+-induced Ca2+ release (CICR) was observed in a pCa 5.8 solution (buffered by 1 mmol l-1 EGTA) as a phasic contraction of variable nature, inhibited by ryanodine (10 µmol l-1), procaine (10 mmol l-1) or benzocaine (5 mmol l-1). Ca2+ release was measured as a function of releasing pCa by using the force­time integral of the caffeine-induced contraction as an estimate of the Ca2+ remaining in the store. After the Ca2+ store had been loaded for 2 min at pCa 6.6, CICR was measured in the presence of 1 mmol l-1 Mg2+, 1 mmol l-1 EGTA and 5 mmol l-1 ATP. The threshold pCa for CICR was 6.0­6.4 under these conditions and more than 90 % of stored Ca2+ was released in 1 min by pCa values in the range 3.5­5.3. Benzocaine totally inhibited the release and promoted extra Ca2+ loading. Preliminary experiments showed a similar caffeine-releasable store in lobster abdominal muscle, which was slightly less sensitive to free [Ca2+]. It is concluded that in crustacean muscle caffeine and micromolar [Ca2+] can release Ca2+ from a ryanodine-sensitive store, which in many respects is similar to the sarcoplasmic reticulum of vertebrate skeletal and cardiac muscle.

Sarcolemma, T-tubules, and subsarcolemmal caveolae. Interrelationships and continuity demonstrated by tannic acid mordanting

1978 ◽  
Vol 56 (3) ◽  
pp. 391-397 ◽  
Author(s):  
T. S. Leeson
Keyword(s):  
Electron Density ◽  
Tannic Acid ◽  
Basal Lamina ◽  
Extracellular Space ◽  
Lead Citrate ◽  
Single Row ◽  
Rectus Abdominus ◽  
Ultrathin Sections ◽  
T Tubules ◽  
Do So

Muscle cells of rat rectus abdominus and diaphragm were mordanted in tannic acid and ultrathin sections, after staining with lead citrate, showed a variable but usually marked increase in electron density of T-tubules, subsarcolemmal caveolae and, to a lesser degree, the plasmalemma, basal lamina material, and associated collagen microfibrils. The technique permits clear demonstration of continuity of the membranes of T-tubules and caveolae with the sarcolemma. While some T-tubules open directly into the extracellular space, others do so indirectly via a caveola. The T-tubules show some variation in diameter and not all are transverse in orientation; they frequently branch, reunite, and run longitudinally, often connecting T-tubules of adjacent triads across a Z-line. Subsarcolemmal caveolae (approximately 100 nm diameter) line the sarcolemma in a single row and show frequent connections by narrow tubules to form dumbell, trefoil, and four-leafed profiles.The findings lead to the conclusion that both T-tubules and caveolae are open to the extracellular space and that T-tubules open both directly and indirectly via caveolae to the surface.

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