scholarly journals Inward rectification in the transverse tubular system of frog skeletal muscle studied with potentiometric dyes.

1985 ◽  
Vol 359 (1) ◽  
pp. 269-291 ◽  
Author(s):  
F M Ashcroft ◽  
J A Heiny ◽  
J Vergara
Keyword(s):  
Skeletal Muscle ◽  
Inward Rectification ◽  
Frog Skeletal Muscle ◽  
Transverse Tubular System ◽  
Tubular System

Inhibition of tetanus tension by elevated extracellular calcium concentration

1981 ◽  
Vol 240 (5) ◽  
pp. C193-C200 ◽  
Author(s):  
J. N. Howell ◽  
K. W. Snowdowne
Keyword(s):  
Skeletal Muscle ◽  
Action Potentials ◽  
Calcium Concentration ◽  
Extracellular Calcium ◽  
Frog Skeletal Muscle ◽  
Transverse Tubular System ◽  
Microelectrode Recordings ◽  
Tubular System ◽  
Osmotic Effects ◽  
Reversible Reduction

Extracellular [Ca2+] in the range of 5-20 mM produces a concentration-dependent reversible reduction in tetanus tension in single frog skeletal muscle fibers. Both peak tension and ability to sustain tension during tetanus is reduced. The effect is unrelated to osmotic effects and independent of stimulation frequency in the range 100-200 Hz. The effect occurs both at 8 and 24 degrees C. Tetanus tension is most strongly inhibited by elevated extracellular [Ca2+] at short muscle lengths, but the effect can be seen at all lengths. Microelectrode recordings during tetanus indicate that action potentials remain undiminished in amplitude and duration throughout the tetanus. The evidence suggests that the inhibition results from a failure of action potentials propagation within the transverse tubular system.

scholarly journals Chloride currents from the transverse tubular system in adult mammalian skeletal muscle fibers

2010 ◽  
Vol 137 (1) ◽  
pp. 21-41 ◽  
Author(s):  
Marino DiFranco ◽  
Alvaro Herrera ◽  
Julio L. Vergara
Keyword(s):  
Skeletal Muscle ◽  
Time Course ◽  
Muscle Fibers ◽  
Optical Data ◽  
Mammalian Skeletal Muscle ◽  
Chloride Currents ◽  
Actual Distribution ◽  
Transverse Tubular System ◽  
Skeletal Muscle Fibers ◽  
Tubular System

Chloride fluxes are the main contributors to the resting conductance of mammalian skeletal muscle fibers. ClC-1, the most abundant chloride channel isoform in this preparation, is believed to be responsible for this conductance. However, the actual distribution of ClC-1 channels between the surface and transverse tubular system (TTS) membranes has not been assessed in intact muscle fibers. To investigate this issue, we voltageclamped enzymatically dissociated short fibers using a two-microelectrode configuration and simultaneously recorded chloride currents (ICl) and di-8-ANEPPS fluorescence signals to assess membrane potential changes in the TTS. Experiments were conducted in conditions that blocked all but the chloride conductance. Fibers were equilibrated with 40 or 70 mM intracellular chloride to enhance the magnitude of inward ICl, and the specific ClC-1 blocker 9-ACA was used to eliminate these currents whenever necessary. Voltage-dependent di-8-ANEPPS signals and ICl acquired before (control) and after the addition of 9-ACA were comparatively assessed. Early after the onset of stimulus pulses, di-8-ANEPPS signals under control conditions were smaller than those recorded in the presence of 9-ACA. We defined as attenuation the normalized time-dependent difference between these signals. Attenuation was discovered to be ICl dependent since its magnitude varied in close correlation with the amplitude and time course of ICl. While the properties of ICl, and those of the attenuation seen in optical records, could be simultaneously predicted by model simulations when the chloride permeability (PCl) at the surface and TTS membranes were approximately equal, the model failed to explain the optical data if PCl was precluded from the TTS membranes. Since the ratio between the areas of TTS membranes and the sarcolemma is large in mammalian muscle fibers, our results demonstrate that a significant fraction of the experimentally recorded ICl arises from TTS contributions.

scholarly journals An improved vaseline gap voltage clamp for skeletal muscle fibers.

1976 ◽  
Vol 67 (3) ◽  
pp. 265-293 ◽  
Author(s):  
B Hille ◽  
D T Campbell
Keyword(s):  
Skeletal Muscle ◽  
Voltage Clamp ◽  
Sodium Current ◽  
Muscle Fibers ◽  
Complex Impedance ◽  
Sodium Currents ◽  
Disk Model ◽  
Transverse Tubular System ◽  
Skeletal Muscle Fibers ◽  
Tubular System

A Vaseline gap potentiometric recording and voltage clamp method is developed for frog skeletal muscle fibers. The method is based on the Frankenhaeuser-Dodge voltage clamp for myelinated nerve with modifications to improve the frequency response, to compensate for external series resistance, and to compensate for the complex impedance of the current-passing pathway. Fragments of single muscle fibers are plucked from the semitendinosus muscle and mounted while depolarized by a solution like CsF. After Vaseline seals are formed between fluid pools, the fiber ends are cut once again, the central region is rinsed with Ringer solution, and the feedback amplifiers are turned on. Errors in the potential and current records are assessed by direct measurements with microelectrodes. The passive properties of the preparation are simulated by the "disk" equivalent circuit for the transverse tubular system and the derived parameters are similar to previous measurements with microelectrodes. Action potentials at 5 degrees C are long because of the absence of delayed rectification. Their shape is approximately simulated by solving the disk model with sodium permeability in the surface and tubular membranes. Voltage clamp currents consist primarily of capacity currents and sodium currents. The peak inward sodium current density at 5 degrees C is 3.7 mA/cm2. At 5 degrees C the sodium currents are smoothly graded with increasing depolarization and free of notches suggesting good control of the surface membrane. At higher temperatures a small, late extra inward current appears for small depolarizations that has the properties expected for excitation in the transverse tubular system. Comparison of recorded currents with simulations shows that while the transverse tubular system has regenerative sodium currents, they are too small to make important errors in the total current recorded at the surface under voltage clamp at low temperature. The tubules are definitely not under voltage clamp control.

The Ultrastructure of the White Striated Myotomal Muscle of the Cod, Gadus morhua

1967 ◽  
Vol 24 (12) ◽  
pp. 2549-2553 ◽  
Author(s):  
C. M. Bishop ◽  
P. H. Odense
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cross Section ◽  
Actin Filaments ◽  
Gadus Morhua ◽  
Striated Muscle ◽  
Fish Muscle ◽  
Transverse Tubular System ◽  
Tubular System ◽  
Myotomal Muscle

The structure of the white skeletal muscle of the cod (Gadus morhua) is described. The peripheral fibrils are ribbon-like and rectangular in cross section with the long axis normal to the sarcolemma. The inner fibrils are mainly polygonal in cross section. Most of the mitochondria and nuclei are peripheral to the fibrils and next to the sarcolemma. The arrangement of the contractile proteins is typical for striated muscle, and the sarcoplasmic reticulum and transverse tubular system are similar to those in other white skeletal fish muscle. A distinct N-band is apparent with indications of branching and reorientation of the actin filaments. Mitochondria are often closely associated with the Z line.

scholarly journals Coordinated Incorporation of Skeletal Muscle Dihydropyridine Receptors and Ryanodine Receptors in Peripheral Couplings of BC3H1 Cells

1997 ◽  
Vol 137 (4) ◽  
pp. 859-870 ◽  
Author(s):  
Feliciano Protasi ◽  
Clara Franzini-Armstrong ◽  
Bernhard E. Flucher
Keyword(s):  
Skeletal Muscle ◽  
Calcium Release ◽  
Surface Membrane ◽  
Ryanodine Receptors ◽  
Freeze Fracture ◽  
Cell Periphery ◽  
Calcium Release Channels ◽  
Transverse Tubular System ◽  
Dihydropyridine Receptors ◽  
Tubular System

Rapid release of calcium from the sarcoplasmic reticulum (SR) of skeletal muscle fibers during excitation–contraction (e–c) coupling is initiated by the interaction of surface membrane calcium channels (dihydropyridine receptors; DHPRs) with the calcium release channels of the SR (ryanodine receptors; RyRs, or feet). We studied the early differentiation of calcium release units, which mediate this interaction, in BC3H1 cells. Immunofluorescence labelings of differentiating myocytes with antibodies against α1 and α2 subunits of DHPRs, RyRs, and triadin show that the skeletal isoforms of all four proteins are abundantly expressed upon differentiation, they appear concomitantly, and they are colocalized. The transverse tubular system is poorly organized, and thus clusters of e–c coupling proteins are predominantly located at the cell periphery. Freeze fracture analysis of the surface membrane reveals tetrads of large intramembrane particles, arranged in orderly arrays. These appear concomitantly with arrays of feet (RyRs) and with the appearance of DHPR/RyS clusters, confirming that the four components of the tetrads correspond to skeletal muscle DHPRs. The arrangement of tetrads and feet in developing junctions indicates that incorporation of DHPRs in junctional domains of the surface membrane proceeds gradually and is highly coordinated with the formation of RyR arrays. Within the arrays, tetrads are positioned at a spacing of twice the distance between the feet. The incorporation of individual DHPRs into tetrads occurs exclusively at positions corresponding to alternate feet, suggesting that the assembly of RyR arrays not only guides the assembly of tetrads but also determines their characteristic spacing in the junction.

Sign in / Sign up

Export Citation Format

Share Document