Table Of ContentLIST OF CONTRIBUTORS
Lloyd Barr Department of ygoloisyhP
University of Illinois
Urbana, Illinois
Nancy .J Boerth Department of ygolohtaP
University of Alabama at Birmingharr
Birmingham, Alabama
reteP Brink stnemtrapeD of ygoloisyhP dna
scisyhpoiB
etatS University of
New York---Stony Brook
Stony Brook, New kroY
kiR sleetsaC Laboratorium voor eigoloisyF
Katholieke Universiteit de nevueL
,grebsiuhtsaG Bruxelles, Belgium
Samuel .K Chacko Pathobiology Department
University of ainavlysnneP
loohcS of Veterinary Medicine
Philadelphia, ainavlysnneP
egroeG .J Christ Departent of Urology
Albert nietsniE College of Medicine
Bronx, New kroY
Odile Cl~ment-Chomienne Department of ygolocamrahP
University of yraglaC
,yraglaC Alberta, adanaC
Wilfiam .C Cole Department of ygolocamrahP
University of yraglaC
,yraglaC Alberta, adanaC
iiv
iiiv TSIL FO SROTUBIRTNOC
Michael DiSanto Division of Urology
ytisrevinU of ainavlysnneP
Philadelphia, ainavlysnneP
Robert .E Garfield Department of ygolocenyG/scirtetsbO
ytisrevinU of saxeT Medical hcnarB
,notsevlaG saxeT
William .£- Gerthoffer Department of ygolocamrahP
ytisrevinU of adaveN
loohcS of Medicine
,oneR adaveN
ellebasI Gorrene Department of Molecular ygoloisyhP
ytisrevinU of Virginia
,ellivsettolrahC Virginia
Bernard Himpens Laboratorium voor eigoloisyF
Katholieke Universiteit de nevueL
,grebsiuhtsaG ,sellexurB Belgium
ikaasaM Ito ehT tsriF Department of Internal
Medicine
Mie University School of Medicine
,usT napaJ
Department of ygolocenyG/scirtetsbO
uneV niaJ
ytisrevinU of saxeT Medical hcnarB
,notsevlaG saxeT
ehT tsriF Department of ygoloisyhP
ieS ihsayaboK
ihcugamaY University
loohcS of Medicine
Ube, napaJ
Padmini salivalamoK Department of ygolohtaP
ytisrevinU of Alabama at Birmingham
Birmingham, Alabama
The tsriF Department of Internal
okusaY Kureishi
Medicine
Mie University School of Medicine
,usT napaJ
tsiL of Contributors xi
Janice .K Larsen tnemtrapeD of Molecular dna
evitargetnI ygoloisyhP
ytisrevinU of Illinois
,anabrU Illinois
samohT .M nlocniL tnemtrapeD of ygolohtaP
ytisrevinU of amabalA ta mahgnimriB
,mahgnimriB amabalA
drahciR .A ssieM tnemtrapeD of scisyhpoiB/ygoloisyhP
anaidnI University loohcS of Medicine
,silopanaidnI anaidnI
giwduL neaissiM muirotarobaL voor eigoloisyF
ekeilohtaK Universiteit ed nevueL
,grebsiuhtsaG ,sellexurB muigleB
okimiK imagoM ehT tsriF Department of ygoloisyhP
ihcugamaY
ytisrevinU loohcS of Medicine
,ebU napaJ
treboR .S Moreland tnemtrapeD of ygolocamrahP dna
ygoloisyhP
PCM nnamenhaH ytisrevinU
,aihpledalihP ainavlysnneP
ihsekaT onakaN ehT tsriF Department of lanretnI
Medicine
Mie University loohcS of Medicine
,usT napaJ
Masato Ohmura ehT tsriF Department of ygoloisyhP
ihcugamaY
ytisrevinU loohcS of Medicine
,ebU napaJ
egroeG .R edaaS tnemtrapeD of ygolocenyG/scirtetsbO
ytisrevinU of saxeT Medical hcnarB
,notsevlaG saxeT
TSIL FO SROTUBIRTNOC
X
nehpetS .M smiS tnemtrapeD of ygoloisyhP
ehT University of nretseW Ontario
,nodnoL Ontario, adanaC
okustaN adekl-ikorodoT ehT tsriF Department of ygoloisyhP
ihcugamaY ytisrevinU
loohcS of Medicine
,ebU napaJ
yrogerG .R edaW tnemtrapeD of ygoloisyhP
ehT University of nretseW Ontario
,nodnoL Ontario, adanaC
nalA .J nieW noisiviD of ygolorU
ytisrevinU of ainavlysnneP
,aihpledalihP ainavlysnneP
ironusaY otomihsoY ehT tsriF Department of ygoloisyhP
ihcugamaY ytisrevinU
loohcS of Medicine
,ebU napaJ
umgnoY gnehZ tnemtrapeD of ygoloibohtaP
ytisrevinU of ainavlysnneP
,aihpledalihP ainavlysnneP
ECAFERP
The idea of this volume was to provide for advanced graduate students, medical
students, and postdoctorals who are beginning to do research related to smooth
muscle a sampling of the orienting ideas of the researchers working on problems
in smooth muscle physiology and pathophysiology. Therefore, an essential goal of
the volume is to identify the lines of investigation that are currently being pursued
by investigators whose concerns are with smooth muscle or with organs with
parenchymal tissues consisting of smooth muscle.
Various types of smooth muscle constitute the parenchyma or characteristic tis-
sues of a large number of organs or regions of organs. In each case, the phenotype
is distinctly different and, while smooth muscles do not exhibit the diversity of
epithelia, they nevertheless span a great range of physiological responsiveness.
Undoubtedly, the variations in the characteristic responses of different smooth
muscles result from the expression of sets of transduction subserving proteins.
However, it is what the sets are and how they work and are regulated that fascinates
the physiologist. In this book, the contrast between sameness and diversity will
recur as a theme.
How do smooth muscles differ? Some are tonic and others are phasic. Some are
sparsely innervated and others are innervated nearly one to one. Some are sponta-
neously active, rhythmically or tonically, while others are normally contracted or
relaxed. While some smooth muscle myocytes generate action potentials, others
never do. Some are activated by norepinepherine and inhibited by acetylcholine,
while others are activated by acetylcholine and inhibited by norepinepherine. Even
ix
xii ECAFERP
though myocytes in all smooth muscle tissues are interconnected by way of gap
junctions, the degree to which they are coupled is quite variable and they subserve
different physiological functions in different smooth muscles. There are hypothe-
ses galore, but the testing of them remains to be done.
Each smooth muscle has a set of characteristics that determine its behavior and
although other smooth muscles may share these attributes, the patterns of their
expression leads to distinctiveness in the smooth muscle tissue physiology. Some
of these characteristics are more useful than others for categorization purposes and
one of the goals of this book is to help identify those qualities that provide better
ways to describe the diversity of smooth muscle. A common way to explain the
diversity of smooth muscle is to say that, in smooth muscle, we have an example
of a great variation in the expression of signal transduction pathways. Of course
the expression of the terminal effector (i.e., the contractile) pathways remain rel-
atively constant and define the tissue. The definition of a smooth muscle myocyte
might be as follows: fusiform interconnected by gap junctions and by nonaligned
actin and myosin filaments. This would correspond to the microscopic observation
that smooth muscle myocytes are identifiable because of both their shape and the
clear expression of a contractible apparatus devoid of the sarcomeric apparatus
found in straited skeletal and cardiac muscles.
Another relevant question is to what extent can various smooth muscle charac-
teristics be grouped together to allow the definition of classes? In current terms,
how many instances of smooth muscle are there? Instead, perhaps we need to dis-
tinguish between more levels of differentiation than we have in the past. Perhaps
we should we decide that each of the organs have different smooth muscle tissues
and should concentrate on new functional and molecular parameters to define cat-
egories. The following might be examples:
A. Receptors: Which kinds of receptors are there for the different kinds of
transmitter, neurohumor, or neuromodulator and what are their associated
signal transduction pathways? Innervation, receptor type, and second-mes-
senger cascade seem to correlate.
B. Connectivity: How well and by which isoforms of connexin are cells con-
nected?
C. Mechanically there is a trade off between those properties that lead to
faster, more transient contractions as opposed to those that lead to slower,
more energetically efficient contractions. Among smooth muscles, some
have a more obvious specialization toward the "latch" mode of contracting.
Will contractile protein isoforms correlate with these functionalities or are
there other determinant proteins?
There is an easy division of smooth muscles into those which are spontaneously
active and those which are completely dependent on innervation for activation.
ecaferP xiii
The channel proteins that are expressed must be the material substrate for these
kinds of differences.
A recurrent cluster of questions swirl around the issue of regulation of the con-
tractile process itself. By analogy to striated muscles, steps other than attachment
may be expected to play important roles in the kinetics of the cross bridge cycle.
What steps other than attachment might be regulated and are important in deter-
mining the mechanical output? Examples include bridge cycle influencing steps,
particularly those that might alter the force per active cross bridge. The bottom line
issue is to determine what is the overall rate at which a muscle can transduce bond
energy into mechanical energy as a function of load. Endurance of the contractile
activity, speed of shortening, and dependence on oxygen are among the other
functions we can begin to identify on a molecular basis.
The primary determinant of force in the present consensus paradigm seems to
be to the number of cross bridges activated. The fraction of time each bridge is
engaged during cycling or the force exerted while being engaged does not seem to
vary so much, so more bridges means more mechanical output. As will be dis-
cussed, mechanisms for the activation of cross bridges include (1) phosphoryla-
tion of myosin, (2) actin-based mechanisms, including those involving caldesmon
and calponin, and (3) other regulatory mechanisms, especially those that occur
downstream from the phosphorylation of myosin. Thus, it is a near consensus that
the primary activating event is the phosphorylation of myosin and the P-myosin/
myosin ratio is expected to be perhaps the most important regulatory parameter.
This ratio is influenced by the relative activity of myosin light chain kinase
(MLCK) and the activities of the several myosin light chain phosphatases. The
possibility also exists that there are other enzymes that either affect the ratio or
activate or deactivate myosin in another ways.
Suffice therefore to say that the extent of smooth muscle diversity and the
underlying mechanisms of action remain interesting open areas of questioning.
Lloyd Barr and George J. Christ
Guest Editors
MECHANICS OF SMOOTH MUSCLE
drahciR A. Meiss
I. Introduction ............................................... 3
A. The Role of Mechanical Studies in Smooth Muscle Research .... 3
B. Special Mechanical Properties Unique to Smooth Muscle ....... 3
C. The Aims and Scope of This Chapter ....................... 4
II. The Basics of Muscle Mechanics ............................... 4
A. Contributions from Classical Muscle Mechanics and
Their Use in the Smooth Muscle Context .................... 4
B. Terms that Describe and Quantify Fundamental Properties ....... 4
C. Terms that Describe the Mechanical Conditions of Contraction... 8
D. Standard Measures of Mechanical Function ................. 12
E. Conceptual Models of Muscle Components and
Their Arrangements .................................... 17
F. Adapting the Classical (Skeletal) Muscle Paradigm to
Smooth Muscle Problems ............................... 18
III. Technical Aspects of Mechanical Measurements ................. 18
A. Establishing Satisfactory Conditions for Measurement ......... 18
B. Instrument and Equipment Considerations .................. 18
C. Choice of Preparations .................................. 22
Advances in Organ Biology, Volume 8, pages 1-48.
Copyright © 2000 by JAI Press Inc.
All rights of reproduction in any form reserved.
ISBN: 0-7623-0613-0
2 RICHARD A. SSIEM
D. Specialized Mechanical Preparations and Measurements ....... 23
IV. The Mechanics of Smooth Muscle ............................. 24
A. Passive Mechanical Properties ............................ 25
B. Early Mechanical Events in Activation ..................... 25
C. Isometric Contraction and Relaxation ...................... 26
D. Isotonic Contraction and Relaxation ....................... 27
E. Characterization of Smooth Muscle Stiffness ................. 29
F. Response to Externally Imposed Changes in
Mechanical Conditions .................................. 32
V. Mechanical Differences between Smooth and Skeletal Muscle ....... 34
A. Special Mechanical States--The "Latch Bridge" Phenomenon... 34
B. Length Dependence of Force and Shortening ................. 36
C. Functional Adaptations of Mechanical Properties ............. 38
D. Structural Constraints on Smooth Muscle Function ............ 40
VI. Current Understanding and Future Trends
in Smooth Muscle Mechanics ................................ 42
A. Current Knowledge of the Mechanism of Contraction .......... 42
B. Trends for the Future ................................... 43
Acknowledgments ......................................... 44
References ............................................... 44
ABSTRACT
The function of smooth muscle, in its wide variety of physiological roles in the
body, requires the changing of metabolic energy into mechanical effects. The
study of the means by which smooth muscle cells and tissues interact physically
with the internal and external environments is the field of muscle mechanics.
Although the mechanical roles of smooth muscle are many and varied, their study
can be organized, guided, and simplified by using the paradigm provided by years
of study of skeletal muscle. This chapter first presents the terminology, functional
relationships, and standard experimental approaches that have arisen largely
through the study of skeletal muscle. After treating the technical requirements for
making reliable and adequate mechanical measurements of smooth muscle func-
tion, specific features of the mechanics of smooth muscle are discussed, compar-
ing and contrasting them with the mechanical properties of skeletal muscle and
pointing out the special features unique to smooth muscle. The current state of
knowledge in the field is briefly surveyed, and areas of current concern and
importance are highlighted.
scinahceM of htoomS elcsuM 3
I. INTRODUCTION
A. The Role of Mechanical Studies in Smooth Muscle Research
Mechanical studies of contraction have been a part of smooth muscle research
for the better part of a century. Most of these studies have been done on largely
intact visceral organs of which smooth muscle is a major and integral part, and
smooth muscle as a contractile system per se was not the primary object of study.
It is within the past 35 years that smooth muscle has come into its own as a subject
for physiological and biophysical studies focused on its specialized contractile and
control mechanisms. To be sure, much smooth muscle research is still carried on
at the organ and system level; these studies now have the additional advantage of
a much more complete understanding of the unique properties of the smooth mus-
cle contraction and control mechanisms, particularly at the molecular level. While
this new knowledge has led to a further appreciation of the similarities and differ-
ences among the many types of smooth muscle, it is still the case that many organ-
and tissue-level studies could benefit from further and more practical application
of specific knowledge of the mechanical properties of smooth muscle.
.B Special Mechanical Properties Unique to Smooth Muscle
Studies of the mechanical properties of skeletal muscle, dating back to the nine-
teenth century, have provided a highly useful framework for the design and anal-
ysis of smooth muscle contraction, and this framework that will be used as an
organizing principle in this chapter. However, although many similarities between
the two muscle types have long been apparent, the growing knowledge of the
marked differences in structure has led to a divergence the paths of muscle
mechanics research, and mechanical studies in skeletal muscle have been pursued
at a high level of biophysical and technical refinement. Many of the methods and
techniques used for the detailed study of skeletal muscle are uniquely related to its
specialized structure (particularly to its regular striation pattern) and cannot be
directly related to smooth muscle function. Nevertheless, they have provided for
an orderly and consistent empirical approach to smooth muscle study. As a result,
the literature of smooth muscle mechanics contains many reports of smooth
mechanical properties that appear quite similar to those of skeletal muscle. In
many cases, however, it is not at all clear that the molecular, cellular, and
tissue-based mechanisms underlying smooth muscle contractile phenomena are
specifically related to those responsible for similar behavior in skeletal muscle.
Modern research has shown significant similarities between smooth and skeletal
muscle at the fundamental molecular level (Harris and Warshaw, 1993; Guilford et
al., 1997; Harris et al., 1994). From a mechanical standpoint, however, there are a
number of critical differences between smooth and skeletal muscle. The most
important of these relate to cellular and tissue structure and modes of the control
