Muscle Biophysics

Muscle contraction has been the focus of scientific investigation for more than two centuries, and major discoveries have changed the field over the years. Early in the twentieth century, Fenn (1924, 1923) showed that the total energy liberated during a contraction (heat + work) was increased when the muscle was allowed to shorten and perform work. The result implied that chemical reactions during contractions were load-dependent. The observation underlying the “Fenn effect” was taken to a greater extent when Hill (1938) published a pivotal study showing in details the relation between heat production and the amount of muscle shortening, providing investigators with the force-velocity relation for skeletal muscles. Subsequently, two papers paved the way for the current paradigm in the field of muscle contraction. Huxley and Niedergerke (1954), and Huxley and Hanson (1954) showed that the width of the A-bands did not change during muscle stretch or activation. Contraction, previously believed to be caused by shortening of muscle filaments, was associated with sliding of the thick and thin filaments. These studies were followed by the classic paper by Huxley (1957), in which he conceptualized for the first time the cross-bridge theory; filament sliding was driven by the cyclical interactions of myosin heads (cross-bridges) with actin. The original cross-bridge theory has been revised over the years but the basic features have remained mostly intact. It now influences studies performed with molecular motors responsible for tasks as diverse as muscle contraction, cell division and vesicle transport.

Muscle contraction has been the focus of scientific investigation for more than two centuries, and major discoveries have changed the field over the years. Early in the twentieth century, Fenn (1924, 1923) showed that the total energy liberated during a contraction (heat + work) was increased when the muscle was allowed to shorten and perform work. The result implied that chemical reactions during contractions were load-dependent. The observation underlying the “Fenn effect” was taken to a greater extent when Hill (1938) published a pivotal study showing in details the relation between heat production and the amount of muscle shortening, providing investigators with the force-velocity relation for skeletal muscles. Subsequently, two papers paved the way for the current paradigm in the field of muscle contraction. Huxley and Niedergerke (1954), and Huxley and Hanson (1954) showed that the width of the A-bands did not change during muscle stretch or activation. Contraction, previously believed to be caused by shortening of muscle filaments, was associated with sliding of the thick and thin filaments. These studies were followed by the classic paper by Huxley (1957), in which he conceptualized for the first time the cross-bridge theory; filament sliding was driven by the cyclical interactions of myosin heads (cross-bridges) with actin. The original cross-bridge theory has been revised over the years but the basic features have remained mostly intact. It now influences studies performed with molecular motors responsible for tasks as diverse as muscle contraction, cell division and vesicle transport.

Thoroughly researched using experimentation and re-examination of all previously published evidence, Molecular and Physiological Mechanisms of Muscle Contraction is a carefully crafted treatise and revision of previous conceptions of muscle contraction. It presents detailed descriptions of new, previously unpublished data and hybrids recent findings with the standard Huxley model. This book demonstrates that traditional concepts cannot fully explain contraction and builds upon previous work. It identifies flaws in the reasoning initially used to explain some results as well as alternative interpretations accounting for inconsistencies. In response to previous bodies of inconsistent or conflicting theories and data, the book synthesizes research based on the Huxley model with more recent experimental and laboratory findings to define a new model. The new model this book proposes is not a replacement for the standard Huxley model of muscle contraction, but a modification based on recent research and synthesized with pre-existing data and conceptions. It reconciles new data with prior information that is contradictory or not entirely explicable in proposing a new integrated and more complete model of muscle contraction.

Physiology, Biophysics and Biomedical Engineering provides a multidisciplinary understanding of biological phenomena and the instrumentation for monitoring these phenomena. It covers the physical phenomena of electricity, pressure, and flow along with the adaptation of the physics of the phenomena to the special conditions and constraints of biolog

This volume presents the proceedings of a muscle symposium, which was supported by the grant from the Fujihara Foundation of Science to be held as the Fourth Fujihara Seminar on October 28 -November 1, 2002, at Hakone, Japan. The Fujihara Seminar covers all fields of natural science, while only one proposal is granted every year. It is therefore a great honor for me to be able to organize this meeting. Before this symposium, I have organized muscle symposia five times, and published the proceedings: " Cross-bridge Mechanism in Muscle Contraction (University of Tokyo Press, 1978), "Contractile Mechanisms in Muscle" (plenum, 1984); "Molecular Mechanisms of Muscle Contraction" (plenum, 1988); "Mechanism of MyofIlament Sliding in Muscle contraction" (plenum, 1993); "Mechanisms of Work Production and Work Absorption in Muscle" (plenum, 1998). As with these proceedings, this volume contains records of discussions made not only after each presentation but also during the periods of General Discussion, in order that general readers may properly evaluate each presentation and the up-to-date situation of this research field. It was my great pleasure to have Dr. Hugh Huxley, a principal discoverer of the sliding fIlament mechanism in muscle contraction, in this meeting. On my request, Dr. Huxley kindly gave a special lecture on his monumental discovery of myofIlament-lattice structure by X-ray diffraction of living skeletal muscle. I hope general readers to learn how a breakthrough in a specific research field can be achieved.

The student of biolo,gical science in his final years as an undergraduate and his first years as a graduate is expected to gain some familiarity with current research at the frontiers of his discipline. New research work is published in a perplexing diversity of publications and is inevitably concerned with the minutiae of the subject. The sheer number of research journals and papers also causes confusion and difficulties of assimilation. Review articles usually presuppose a background knowledge of the field and are inevitably rather restricted in scope. There is thus a need for short but authoritative introductions to those areas of modern biological research which are either not dealt with in standard introductory textbooks or are not dealt with in sufficient detail to enable the student to go on from them to read scholarly reviews with profit. This series of books is designed to satisfy this need. The authors have been asked to produce a brief outline of their subject assuming that their readers will have read and remembered much of a standard introductory textbook of biology. This outline then sets out to provide by building on this basis, the conceptual framework within which modern research work is progressing and aims to give the reader an indication of the problems, both conceptual and practical, which must be overcome if progress is to be maintained.

The biophysics of excitable membranes and extracellular potential .fields emerged at the end of the 18th century, together with electrophysiology. and has been used ever since as a basis for the development of electrophysiological 'tnvestigations. This holds true even for the contemporary stage of initial discoveries concerning the molecular mechanisms of membrane excitability. The biophysics of ionic channels has gradually revealed the genesis of the ionic currents and of the biopotentials in ditIercnt excitable structures. On the basis of electrodynamics, the extracellular potential fields in the living body. ~nsidcred as a volume conductor, have been studied intensively. The knowledge accumulated constitutes the theoretical basis for interpretation of the electrophysiological data. Over a period of more than 15 years a group of Bulgarian investigators led by A. Gydikov has systematically studied the dependence between the intra- and extracellular potentials of the skeletal muscles. The present book summarizes these investigations known in many countries. Using a great amount of factual material from experiments and model investigations on the skeletal muscle potentials, the author considers: a) the extracellular potential field of single skeletal muscle fibres and their dependence on the parameters of intracellular action potentials, the geometric parameters ofthe fibres.and ofthe volume conductor; b) the potentials of single motor units; c) the compound and reflex muscle potentials, and d) the interference electromyogram.

Molecular biophysics is a rapidly growing field of research that plays an important role in elucidating the mysteries of life's molecules and their assemblies, as well as the relationship between their structure and function. Introduction to Molecular Biophysics fills an existing gap in the literature on this subject by providing the reader with th