Morphology and accessibility of the ‘transverse’ tubular system in frog sartorius muscle after glycerol treatment

An electron microscopic study of rabbit and human myocardium provides further evidence of the existence of two distinct components of the sarcoplasmic reticulum. A thin-walled tubular system (termed longitudinal system) is arranged in anastomosing channels sur-surrounding each sarcomere and has transverse and possibly also longitudinal connections with the tubules of adjacent sarcomeres. A thick-walled tubular system traverses the myofiber transversely at the level of the Z lines of the myofibrils. The structure of these tubules very closely resembles that of deep sarcolemmal invaginations. Indeed, the membranes of the tubules appear to be continuous with the sarcolemma in favorable sections so that there seems to be an extension of the cell membrane and extracellular fluid to all depths of the myocardial fiber. Certain physiologic data which support this concept are discussed. The calculations of A. V. Hill comparing the kinetics of diffusion and the time-distance relationships between excitation and activation in frog sartorius muscle are reconsidered for cardiac muscle.

Download Full-text

Some Relations between Changes in the Linear Electrical Properties of Striated Muscle Fibers and Changes in Ultrastructure

The Journal of General Physiology ◽

10.1085/jgp.50.10.2437 ◽

1967 ◽

Vol 50 (10) ◽

pp. 2437-2458 ◽

Cited By ~ 30

Author(s):

W. H. Freygang ◽

S. I. Rapoport ◽

L. D. Peachey

Keyword(s):

Electrical Properties ◽

Time Constant ◽

Striated Muscle ◽

Sartorius Muscle ◽

Transverse Tubular System ◽

Tubular System ◽

In Series ◽

Striated Muscle Fibers ◽

Frog Sartorius ◽

Good Agreement

Some of the linear electrical properties of frog sartorius muscle have been investigated in Ringer's fluid and in a Ringer fluid made hypertonic by the addition of sucrose or NaCl. Electrical constants were determined from measurements of the phase angle of the admittance of a fiber for an applied alternating current, from measurements of the voltage induced by an inward pulse of current, and from measurements of the conduction velocity of the action potential and the time constant of its foot. The dilation of the transverse tubular system induced by the sucrose hypertonic Ringer fluid was correlated with the change in the electrical constants. From this it is concluded that a two time constant equivalent circuit for the membrane, as proposed by Falk and Fatt, is in good agreement with our results. Both the area of the membrane of the transverse tubular system, and the capacity (ce) attributed to it, increased in the sucrose hypertonic Ringer fluid. The resistance re, which is in series with ce, did not fall when the transverse tubular system was dilated and probably is not located in that system.

Download Full-text

The effect of nitrate ion on glycerol-treated frog skeletal muscle fibers

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y70-116 ◽

1970 ◽

Vol 48 (12) ◽

pp. 813-816 ◽

Cited By ~ 2

Author(s):

A. R. Luff ◽

H. L. Atwood

Keyword(s):

Time Constant ◽

Surface Membrane ◽

Muscle Fibers ◽

Effective Resistance ◽

Sartorius Muscle ◽

Nitrate Ion ◽

Transverse Tubular System ◽

A Value ◽

Tubular System ◽

Frog Sartorius

The effect of nitrate ion on glycerol-treated, frog sartorius muscle fibers was investigated. Glycerol treatment alone (which has been shown to disrupt the transverse tubular system of the fiber) caused a considerable reduction in the time constant of the fiber membrane, but the effective resistance was virtually unchanged. Exposure of normal fibers to nitrate ion produced an increase in both the effective resistance and the time constant. Glycerol-treated fibers exposed to nitrate ion showed an increase in both the effective resistance and the time constant. The latter increased to a value in excess of that found in the normal fibers. The effect of nitrate ion on membrane electrical properties appeared to result from its action on the surface membrane as opposed to the transverse tubules.

Download Full-text

Action Potentials, Afterpotentials, and Excitation-Contraction Coupling in Frog Sartorius Fibers without Transverse Tubules

The Journal of General Physiology ◽

10.1085/jgp.53.3.298 ◽

1969 ◽

Vol 53 (3) ◽

pp. 298-310 ◽

Cited By ~ 91

Author(s):

Peter W. Gage ◽

Robert S. Eisenberg

Keyword(s):

Membrane Potential ◽

Short Duration ◽

Action Potentials ◽

Sartorius Muscle ◽

Transverse Tubules ◽

Excitation Contraction Coupling ◽

Transverse Tubular System ◽

Contraction Coupling ◽

Tubular System ◽

Frog Sartorius

In frog sartorius muscle fibers in which the transverse tubular system has been disrupted by treatment with glycerol, action potentials which are unaccompanied by twitches can be recorded. These action potentials appear to be the same as those recorded in normal fibers except that the early afterpotential usually consists of a small hyperpolarization of short duration. After a train of action potentials no late afterpotential is seen even when the membrane potential is changed from the resting level. In fibers without transverse tubules hyperpolarizing currents do not produce a creep in potential. The interruption of excitation-contraction coupling, the changes in the afterpotentials, and the disappearance of creep are all attributed to the lack of a transverse tubular system.

Download Full-text