Prior to the emergence of the sliding filament model, contraction theories had been in abundance. In the absence of the kinds of structural and biochemical information available today, it has been a simple matter to speculate about the possible ways in which tension generation and shortening might occur. The advent of the sliding filament model had an immediate impact on these theories; within several years they fell by the wayside, and attention was redirected towards mechanisms by which the filaments might be driven to slide by one another. In terms of identifying the driving mechanism, the pivotal observa­ tion was the electron micrographic indentification of cross-bridges extending from the thick filaments. It was quite naturally assumed that such bridges, which had the ability to split ATP, were the molecular motors, i.e., that they were the sites of mechanochemical transduction. Out of this presumption grew the cross-bridge model. in which filament sliding is presumed to be driven by the cyclic interaction of cross-bridges with complementary actin sites located along the thin filaments.

Inhalt

I: Structural Dynamics.- Structure of the Myofilaments.- Symmetry and Self-Assembly in Vertebrate A-Filaments.- Image Analysis of the Complex of Actin-Tropomyosin and Myosin Subfragment 1.- A-Band Mass Exceeds Mass of its Filament Components by 30-45%.- Myofilament Diameters: An Ultrastructural Re-Evaluation.- Do Thick Filaments Shorten?.- Limulus Striated Muscle Provides an Unusual Model for Muscle Contraction.- Dynamic Laser Light Scattering of Papain-Treated Thick Filaments from Limulus Striated Muscle in Suspension.- Structure of Limulus and Other Invertebrate Thick Filaments.- Cinematographic Studies on the A-Band Length Changes During Ca-Activated Contraction in Horseshoe Crab Muscle Myofibrils.- Contraction Bands: Differences Between Physiologically vs. Maximally Activated Single Heart Muscle Cells.- Structural Studies of Glycerinated Skeletal Muscle. A-Band Length and Cross-Bridge Period in ATP-Contracted Fibers.- X-Ray Diffraction Approaches to Structural Dynamics.- Time Resolved X-Ray Diffraction Studies of Cross-Bridge Movement, and Their Interpretation.- On the Possibility of Interaction Between Neighbouring Crossbridges.- Cross-Bridge States in Invertebrate Muscles.- Factors Affecting the Equatorial X-Ray Diffraction Pattern from Contracting Frog Skeletal Muscle.- Effect of Stretch on the Equatorial X-Ray Diffraction Pattern from Frog Skeletal Muscle in Rigor.- Structural Studies of Muscle During Force Development in Various States.- Muscle Crossbridge Positions from Equatorial Diffraction Data: An Approach Towards Solving the Phase Problem.- Configurations of Myosin Heads in the Crab Striated Muscle as Studied by X-Ray Diffraction.- On the Intensity Reversal of the "Tropomyosin Reflexions" in X-Ray Diffraction Patterns From Crab Striated Muscle.- Structural Basis of Forces in Resting Muscle.- Cross-Bridge Attachment in Relaxed Muscle.- Cytoskeletal Matrix in Striated Muscle: The Role of Titin, Nebulin and Intermediate Filaments.- Connecting Filaments, Core Filaments and Side Struts: A Proposal to Add Three New Load-Bearing Structures to the Sliding Filament Model.- The Composition of the Intracellular Milieu.- 31P NMR Studies of Resting Muscle in Normal Human Subjects.- Intracellular pH and Energy Changes in Muscle.- Change in Fixed Charge in the Thick Filament Lattice of Limulus Striated Muscle with Sarcomere Shortening.- A New Method to Measure Intracellular Diffusible Elemental Concentration.- Ion Concentrations Surrounding the Myofilaments.- Do Cross-Bridges Rotate during Contraction?.- The Nature of the Actin - Cross-Bridge Interaction.- Cross Linking Studies Related to the Location of the Rigor Compliance in Glycerinated Rabbit Psoas Fibers: Is the S-2 Portion of the Cross-Bridge Compliant?.- Angles of Fluorescently Labelled Myosin Heads and Actin Monomers in Contracting and Rigor Strained Muscle Fiber.- Muscle Cross-Bridges: Do They Rotate?.- An Actomyosin Motor.- Concluding Discussion.- Structural Dynamics: Implications for Contractile Mechanisms.- II: Mechanics, Energetics and Molecular Models.- Length-Tension Relations.- Changes in Intracellular Ca2+ Induced by Shortening Imposed During Tetanic Contractions.- Sarcomere Length Changes in Single Frog Muscle Fibers During Tetani at Long Sarcomere Lengths.- Length-Tension-Velocity Relationships Studied in Short Consecutive Segments of Intact Muscle Fibres of the Frog.- Force - Sarcomere-Length Relation and Filament Length in Rat Extensor Digitorum Muscle.- Some Specific Predictions and Experiments on Single Myofibrillar Mechanics.- 1kgf/cm2 - The Isometric Tension of Muscle Contraction: Implications to Cross-Bridge and Hydraulic Mechanisms.- General Discussion: Length-Tension Relations.- Activation of the Myofilaments.- Calcium Sensitivity is Modified by Contraction.- Changes in [Ca2+]i Induced by Rapid Cooling of Single Skeletal Muscle Fibres Treated with Low Concentration of Caffeine.- Contractile Responses to MgATP and pH in a Thick Filament Regulated Muscle: Studies with Skinned Scallop Fibers.- Formation of Calcium-Parvalbumin Complex During Contraction. A Source of "Unexplained Heat"?.- Tension Transients and Stiffness.- Symmetric and Asymmetric Processes in the Mechano-Chemical Conversion in the Cross-Bridge Mechanism Studied by Isometric Tension Transients.- A Comparison of Muscle Stiffness Measurements Obtained with Rapid Releases or Stretches of Frog Semitendinosus Fibers.- Tension Transients in Skinned Muscle Fibres of Insect Flight Muscle and Mammalian Cardiac Muscle: Effect of Substrate Concentration and Treatment with Myosin Light Chain Kinase.- Tension Transients in Single Isolated Smooth Muscle Cells.- Sarcomere Length and Force Changes in Single Tetanized Frog Muscle Fibers Following Quick Changes in Fiber Length.- Analysis of Mechanical Behavior of Muscle by a Multi-Sarcomere Model.- The Kinetics of Cross-Bridge Attachment and Detachment Studied by High Frequency Stiffness Measurements.- The Role of Ca2+ in Cross-Bridge Kinetics in Chemically Skinned Rabbit Psoas Fibers.- Muscle Stiffness Changes During Isometric Contraction in Frog Skeletal Muscle as Studied by the Use of Ultrasonic Waves.- General Discussion: Interpretation of Stiffness Measurements.- Influence of Myofilament Lattice Dimensions on Contractile Function.- Force Response to Width and Length Perturbations in Compressed Skinned Skeletal Muscle Fibers.- Lateral Shrinkage of the Myofilament Lattice in Chemically Skinned Muscles During Contraction.- Effect of Lattice Spacing on Cross-Bridge Orientations in Relaxed Crab Muscle.- Isotonic Contraction of Temp-Step Activated Muscle Fibers with Varied Tonicity: Effects of Cell Volume and the Degree of Activation.- Changes in Mechanical Properties in Osmotically Compressed Skinned Muscle Fibers of Frog.- Contraction Dynamics.- Stretch of Contracting Muscle Fibres: Evidence for Regularly Spaced Active Sites Along the Filaments and Enhanced Mechanical Performance.- Velocity Sensitivity of Yielding During Stretch in the Cat Soleus Muscle.- Force-Velocity Relation and Stiffness in Frog Single Muscle Fibres During the Rise of Tension in an Isometric Tetanus.- Stepwise Shortening: Evidence and Implications.- A Proposed Mechanism of Contraction in Which Stepwise Shortening is a Basic Feature.- Stepwise Changes in Crossbridge State and Sarcomere Length: Do Lattice Constraints Play a Critical Role?.- Distilled Water-Induced Contractions in Dehydrated and Skinned Muscle Fibers.- Cardiac Muscle Mechanics.- Modeling of Cardiac Muscle Contraction Based on the Cross-Bridge Mechanism.- The Dependence of Force and Velocity on Calcium and Length in Cardiac Muscle Segments.- Non-Uniformity of Contraction and Relaxation of Mammalian Cardiac Muscle.- Transient Length Responses of Heart Muscle in Ba2+-Contracture to Step Tension Reductions.- Energetics.- Dependence …