Kinetics of Muscle Contraction and Relaxation Bin Liu Ph.D. Phone: (614) 292-3925 Email: liu.591@osu.edu DHLRI 525 Department of Physiology and Cell Biology, The Ohio State University

Factors Controlling SPEED of Movement Environmental Whole Body Muscle (Organ) Muscle (Cellular) Muscle (Molecular)

Ultimate Factors Controlling SPEED

Need the Strength to Meet the Demand Motor Units and Recruitment

Amplifying Velocity/Distance - Lever Systems, Muscle Length and Geometry Levers Detrimental to Force Levers Amplify Distance/Velocity

Energy Supply Also Controls SPEED Glycolytic Sources SUPPORT Speed BUT NOT Duration Oxidation Sustains Duration BUT NOT Speed

Striding Requires Contraction and Relaxation For Sustained SPEEDS the Muscle Groups Must Contract as well as Relax – Otherwise No Continued Movement

SPEED Is Determined by Fiber Types and Fatigue Different Fiber Types Contract and Relax at Different Rates Fatigue Can Slow the Rates of Contraction and Relaxation – Again a Fiber Type Phenomenon

Cellular Regulation of Muscle Contraction 1) Action Potential 2) Calcium Transient Plasma Membrane Plasma Membrane Sarcoplasmic Reticulum [Ca2+] T-Tubule Sarcoplasmic Reticulum SR Ca2+ ATPase Time Calcium 3) Calcium Binds Troponin C 4) Myosin Power Stroke 5) Force Production Actin Actin –Ca2+ Relaxed Tropomyosin Troponin Complex - Ca2+ Actin Myosin Myosin + Ca2+ Myosin Binding Site +Ca2+ Contracted ATP Driven Power Stroke

The Action Potential, Rise in Calcium and Activation of the Thin Filament All Occur Much Faster than Contraction Calcium Transient (Shortening or Force Generation)

Biochemical Rate Limiting Step of Contraction (Coupling of the Chemical Changes to Mechanical Changes) Rate-Limiting Step for Contraction The Myosin Neck is also a Lever Arm POWER STROKE Associated with Pi Release

ATPase Rate Correlates with Maximal Speed of Muscle Contraction

The Load that Myosin Has to Work Against Alters Velocity Maximal Velocity (VMAX) Tug-of-War To bear the load more myosins need to be simultaneously bound leading to drag. D A C B B A C Even at the single molecule level velocity slows due to ADP release slowing with load. D

Different Fiber Types Contract and RELAX at Different Rates - ADP ~250 Hz Super Fast Fast Slow ~200 Hz ~90 Hz ~5 Hz ~2 Hz

1 3 2 Ca2+ Off TnC Cross Bridge Dissociation Three Biochemical Influences on Striated Muscle Relaxation 1 2 3 Fall in the Ca2+ Transient Ca2+ Off TnC Cross Bridge Dissociation Actin Actin Tropomyosin Troponin Complex [Ca2+] - Ca2+ Amp Actin Myosin Myosin Time Time + Ca2+ Myosin Binding Site ATP Driven Power Stroke

Inhibition of the SR Ca2+-ATPase Inhibits Relaxation: Ca2+ Levels Must Decline for Relaxation to Occur TBQ Inhibition of SR Ca2+-ATPase X X SR Ca2+ ATPase Control

Parvalbumin Acts as a Delayed and Temporary Ca2+ Buffer Parvalbumin Increases the Rate of Muscle Relaxation by Giving the SR Ca2+-ATPase a Helping EF-Hand +Parv - Parv Parvalbumin Acts as a Delayed and Temporary Ca2+ Buffer Mg-Parv Ca-Parv Ca2+ Displaces Mg2+ from Parv SR Ca2+ ATPase SR Removes Ca2+ from Parv

The EF-Hand is the Most Common Calcium Binding Motif used to Decode the Calcium Signal Crystal Structure of Cardiac TnC EF-Hand Canonical Calcium Binding Loop N-Terminal Regulatory Domain Loop Helix Helix C-Terminal Structural Domain > 500 known EF-hand proteins with >300 unique sequences What is the significance? >1000-fold variation in affinity and rate constants

The Regulatory Domain of Troponin C Acts as a Ca2+ Dependent Switch The Troponin Complex Contains Three Proteins Ca2+ Troponin C – Binds Calcium Troponin I – Inhibits Cross-Bridge Binding Troponin T – Binds Tropomyosin Ca2+ TnI Apo State Ca2+ Saturated Ca2+ Saturated + TnI

Effect of ‘Slower’ or ‘Faster’ Troponin C Mutants on Skeletal Muscle Relaxation Ca2+ Dissociation Rates from Fluorescent TnC Mutants Rates of Relaxation with TnC Mutants Control TnC Slower TnC (5/s) Faster TnC Slower TnC control TnC (11/s) Faster TnC (16/s)

CLASSIFICATION OF SKELETAL MUSCLE FIBERS - All Systems “TUNED” for a Particular Function - Classification system of muscle fibers is based on: Rate of ATP utilization and capacity to re-synthesize ATP Physiological implications of these parameters Muscles are heterogeneous with different proportions of fiber types depending on function

Assorted References (contact me if you would like more) Studies in Biology #11: Muscle. 2nd Edition, D.R. Wilkie 1979. Human Physiology, 9th edition by E.P. Widmaier, H. Raff and K.T. Strang, 2004 News Physiol Sci. 2001 Apr;16:49-55. Skeletal and cardiac muscle contractile activation: tropomyosin "rocks and rolls". Gordon AM, Regnier M, Homsher E. Pflugers Arch. 2005 Mar;449(6):505-17. Epub 2004 Nov 30. Sarcomeric determinants of striated muscle relaxation kinetics. Poggesi C, Tesi C, Stehle R. Annu Rev Physiol. 2005;67:39-67. Calcium, thin filaments, and the integrative biology of cardiac contractility. Kobayashi T, Solaro RJ. Am J Physiol. 1996 Feb;270(2 Pt 1):C411-7. Parvalbumin relaxes frog skeletal muscle when sarcoplasmic reticulum Ca(2+)-ATPase is inhibited. Jiang Y, Johnson JD, Rall JA. Annu Rev Physiol. 2006;68:193-221; Design and Function of Superfast Muscles: New Insights into the Physiology of Skeletal Muscle. Rome LC.