Physiology and Biochemistry

Geoffrey Bourne

• Publisher: Academic Press
• Year: 2014
• Print ISBN: 9780121191030
• eBook ISBN: 9780323161558
• Edition: 2
• Topic: Social Sciences
• Subtopic: Physical Anthropology
• Index: Social Sciences

The Structure and Function of Muscle, Second Edition, Volume III: Physiology and Biochemistry presents the physiology and biochemistry of muscle. This book discusses the various aspects of the structure of muscles and explores some aspects of muscle disease. Organized into 10 chapters, this edition begins with an overview of the transverse tubular system or T system of striated muscle. This text then examines the properties and function of membranes through electron microscopy. Other chapters consider in more detail from a biophysical viewpoint certain aspects of the series of events surrounding muscle contraction. This book discusses as well the significance of the central circulation and the amount of oxygen that can be delivered by the cardiovascular system. The final chapter deals with the heat output and chemical breakdown during an isometric twitch. This book is a valuable resource for scientists, neurobiologists, biologists, biochemists, physiologists, histologists, cytologists, and research workers.

1

ELECTRICAL PROPERTIES OF THE TRANSVERSE TUBULAR SYSTEM

LEE D. PEACHEY and RICHARD H. ADRIAN

Publisher Summary

This chapter discusses the electrical properties of the transverse tubular system. The electrical properties of nerve and muscle are analyzed in terms of the ionic and capacity currents flowing across the cell surface membrane. Morphological evidence suggests that the tubular system can be represented in frog twitch striated muscle fibers as a set of regular two-dimensional tubular networks in which the tubular diameter is smaller than the mesh and the mesh is smaller than the fiber diameter. Access resistance occurs because of constriction of the tubular lumen at the fiber surface or tortuosity of the tubular path near the surface. Either an increased tubular length or a reduced luminal caliber over a significant length increases the radial resistance near the fiber surface. The chapter also presents a linear and a nonlinear method for obtaining the spatial distribution of potential in the tubular system.

I. Introduction

II. Mathematical Analysis

A. Cable Analysis as a Network

B. Introduction of an Access Resistance

C. Tubular Length Constant and Resistance

D. Numerical Method of Analysis

III. Tubular Capacity—Lumped or Distributed?

IV. Excitation–Contraction Coupling

References

I Introduction

The transverse tubular system or T system of striated muscle was discovered by electron microscopy in the 1950s. The most important paper of that period (Porter and Palade, 1957) described the structure we now call the T system as rows of vesicles in the space between the terminal cisternae of the sarcoplasmic reticulum (SR) and termed it the “intermediary vesicles.” This analysis, in effect, included the T system as part of the SR. Since that time, through further comparative studies and the use of improved preparation methods, electron microscopists have demonstrated convincingly that the T system is a branched network of tubules derived from and remaining attached to the surface plasma membrane of the muscle fiber. This has fostered a general feeling that the T system should not be considered as a part of the SR, but as part of the surface membrane complex of the cell. To be sure, it is found deep in the fiber, and it associates closely and in a specific way with the intracellular SR, but in an important respect it is part of the fiber surface membrane.

Of greatest interest to us are the function and physiological properties of the T system. Several recent physiological and morphological studies have been directed to this problem, and work in this area continues actively at present. Our aim in this chapter will be to review the present state of our knowledge, and to indicate some of the uncertainties and possible future directions for advance. We also hope to resolve some uncertainties and apparent discrepancies in earlier papers by presenting an analysis of the T system as a cable network with special properties at the surface of the fiber and with nonlinear properties in its membrane.

II Mathematical Analysis

A Cable Analysis as a Network

The electrical properties of nerve and muscle have been analyzed in terms of the ionic and capacity currents flowing across the cell surface membrane. The basis of this approach is a set of equations that has become known as “cable theory” because of its application to transmission cables. If we are to understand the operation of the T system as a passive electrical network with linear properties, or as a structure generating its own active potential changes, it is necessary as a first step to extend the equations of one-dimensional cable theory to two- and even three-dimensional cable networks representing the T system structure.

Morphological evidence suggests that we can represent the T system in frog twitch striated muscle fibers as a set of regular two-dimensional tubular networks in which the tubular diameter is small compared to the mesh and in which the mesh itself is small compared to the fiber diameter, as done by Adrian et al. (1969a). Tubules are thought to be present between all the fibrils throughout the cross section of the fiber. This is probably the general pattern in vertebrate striated fibers, although there is evidence of scanty longitudinal elements of the T system in some fiber types, for example, frog twitch fibers (Eisenberg and Eisenberg, 1968). In frog slow fibers (Page, 1965; Flitney, 1971), the longitudinally oriented T tubules may make up a substantial fraction of the whole T system. In this case, it is probable that the T system approximates more closely to a three-dimensional network than to a two-dimensional network. For generality, therefore, we shall derive a T system cable equation in three dimensions. Cases of two-dimensional networks, with or without radial symmetry, are special cases of the general equation and may be treated by setting appropriate terms in the general equation to zero.

Since the muscle fiber is cylindrical, the networks to be considered will be limited by the surface of a cylinder, and for T systems with negligible longitudinal connections, the network is in the shape of a circular disk with the same radius as the fiber (Fig. 1). Cylindrical and polar coordinate systems are therefore appropriate for the cable equations.

Fig. 1 Drawing of a muscle fiber cut across through one T system network. The openings of other T system networks are seen along the length of the muscle fiber. Not all tubules near the sur...

Table of contents

• Cover image
• Title page
• Table of Contents
• CONTRIBUTORS
• Copyright
• LIST OF CONTRIBUTORS
• PREFACE
• PREFACE TO THE FIRST EDITION
• CONTENTS OF OTHER VOLUMES
• Chapter 1: ELECTRICAL PROPERTIES OF THE TRANSVERSE TUBULAR SYSTEM
• Chapter 2: THE NEUROMUSCULAR JUNCTION—THE ROLE OF ACETYLCHOLINE IN EXCITABLE MEMBRANES
• Chapter 3: SOME ASPECTS OF THE BIOPHYSICS OF MUSCLE
• Chapter 4: ENERGY NEED, DELIVERY, AND UTILIZATION IN MUSCULAR EXERCISE
• Chapter 5: THE CONTROL OF MUSCULAR ACTIVITY BY THE CENTRAL NERVOUS SYSTEM
• Chapter 6: ELECTROMYOGRAPHY
• Chapter 7: PROTEINS OF THE MYOFIBRIL
• Chapter 8: BIOCHEMISTRY OF MUSCLE
• Chapter 9: BIOCHEMISTRY OF MUSCLE MITOCHONDRIA
• Chapter 10: ATP BREAKDOWN FOLLOWING ACTIVATION OF MUSCLE
• AUTHOR INDEX
• SUBJECT INDEX