Muscle Biophysics Research Articles

Biophysical Mechanisms of Vaginal Smooth Muscle Contraction: The Role of the Membrane Potential and Ion Channels.

The vagina is an essential component of the female reproductive system and is responsible for providing female sexual satisfaction. Vaginal smooth muscle contraction plays a crucial role in various physiological processes, including sexual arousal, childbirth, and urinary continence. In pathophysiological conditions, such as pelvic floor disorders, aberrations in vaginal smooth muscle function can lead to urinary incontinence and pelvic organ prolapse. A set of cellular and sub-cellular physiological mechanisms regulates the contractile properties of the vaginal smooth muscle cells. Calcium influx is a crucial determinant of smooth muscle contraction, facilitated through voltage-dependent calcium channels and calcium release from intracellular stores. Comprehensive reviews on smooth muscle biophysics are relatively scarce within the scientific literature, likely due to the complexity and specialized nature of the topic. The objective of this review is to provide a comprehensive description of alterations in the cellular physiology of vaginal smooth muscle contraction. The benefit associated with this particular approach is that conducting a comprehensive examination of the cellular mechanisms underlying contractile activation will enable the creation of more targeted therapeutic agents to control vaginal contraction disorders.

Oscillatory work and the step that generates force in single myofibrils from rabbit psoas.

The elementary molecular step that generates force by cross-bridges (CBs) in active muscles has been under intense investigation in the field of muscle biophysics. It is known that an increase in the phosphate (Pi) concentration diminishes isometric force in active fibers, indicating a tight coupling between the force generation step and the Pi release step. The question asked here is whether the force generation occurs before Pi release or after release. We investigated the effect of Pi on oscillatory work production in single myofibrils and found that Pi-attached state(s) to CBs is essential for its production. Oscillatory work is the mechanism that allows an insect to fly by beating its wings, and it also has been observed in skeletal and cardiac muscle fibers, implying that it is an essential feature of all striated muscle types. With our studies, oscillatory work disappears in the absence of Pi in experiments using myofibrils. This suggests that force is generated during a transition between steps of oscillatory work production, and that the states involved in force production must have Pi attached. With sinusoidal analysis, we obtained the kinetic constants around the Pi release steps, established a CB scheme, and evaluated force generated (and supported) by each CB state. Our results demonstrate that force is generated before Pi is released, and the same force is maintained after Pi is released. Stretch activation and/or delayed tension can also be explained with this CB scheme and forms the basis of force generation and oscillatory work production.

Cardiac muscle regulatory units are predicted to interact stronger than neighboring cross-bridges

Strong interactions between cross-bridges (XB) and regulatory units (RU) lead to a steep response of cardiac muscle to an increase in intracellular calcium. We developed a model to quantitatively assess the influence of different types of interactions within the sarcomere on the properties of cardiac muscle. In the model, the ensembles consisting of cross-bridge groups connected by elastic tropomyosin are introduced, and their dynamics is described by a set of partial differential equations. Through large scans in the free energy landscape, we demonstrate the different influence of RU-RU, XB-XB, and XB-RU interactions on the cooperativity coefficient of calcium binding, developed maximal force, and calcium sensitivity. The model solution was fitted to reproduce experimental data on force development during isometric contraction, shortening in physiological contraction, and ATP consumption by acto-myosin. On the basis of the fits, we quantified the free energy change introduced through RU-RU and XB-XB interactions and showed that RU-RU interaction leads to ~ 5 times larger change in the free energy profile of the reaction than XB-XB interaction. Due to the deterministic description of muscle contraction and its thermodynamic consistency, we envision that the developed model can be used to study heart muscle biophysics on tissue and organ levels.

The load dependence and the force-velocity relation in intact myosin filaments from skeletal and smooth muscles.

In the present study we evaluated the load dependence of force produced by isolated muscle myosin filaments interacting with fluorescently labeled actin filaments, using for the first time whole native myosin filaments. We used a newly developed approach that allowed the use of physiological levels of ATP. Single filaments composed of either skeletal or smooth muscle myosin and single filaments of actin were attached between pairs of nano-fabricated cantilevers of known stiffness. The filaments were brought into contact to produce force, which caused sliding of the actin filaments over the myosin filaments. We applied load to the system by either pushing or pulling the filaments during interactions and observed that increasing the load increased the force produced by myosin and decreasing the load decreased the force. We also performed additional experiments in which we clamped the filaments at predetermined levels of force, which caused the filaments to slide to adjust the different loads, allowing us to measure the velocity of length changes to construct a force-velocity relation. Force values were in the range observed previously with myosin filaments and molecules. The force-velocity curves for skeletal and smooth muscle myosins resembled the relations observed for muscle fibers. The technique can be used to investigate many issues of interest and debate in the field of muscle biophysics.

Cardiac Muscle Regulatory Units are Predicted to Interact Stronger than Neighboring Cross-Bridges

Strong interactions between cross-bridges (XB) and regulatory units (RU) lead to a steep response of cardiac muscle to an increase in intracellular calcium. We developed a model to quantitatively assess the influence of different types of interactions within the sarcomere on the properties of cardiac muscle. In the model, the ensembles consisting of cross-bridge groups connected by elastic tropomyosin are introduced, and their dynamics is described by a set of partial differential equations. Through large scans in the free energy landscape, we demonstrate the different influence of RU-RU, XB-XB, and XB-RU interactions on the cooperativity coefficient of calcium binding, developed maximal force, and calcium sensitivity. The model solution was fitted to reproduce experimental data on force development during isometric contraction, shortening in physiological contraction, and ATP consumption by acto-myosin. On the basis of the fits, we quantified the free energy change introduced through RU-RU and XB-XB interactions and showed that RU-RU interaction leads to ~ 5 times larger change in the free energy profile of the reaction than XB-XB interaction. Due to the deterministic description of muscle contraction and its thermodynamic consistency, we envision that the developed model can be used to study heart muscle biophysics on tissue and organ levels.

A Method for the Analysis of AP Foot Convexity: Insights into Smooth Muscle Biophysics.

Action potential (AP) profiles vary based on the cell type, with cells of the same type typically producing APs with similar shapes. But in certain syncytial tissues, such as the smooth muscle of the urinary bladder wall, even a single cell is known to exhibit APs with diverse profiles. The origin of this diversity is not currently understood, but is often attributed to factors such as syncytial interactions and the spatial distribution of parasympathetic nerve terminals. Thus, the profile of an action potential is determined by the inherent properties of the cell and influenced by its biophysical environment. The analysis of an AP profile, therefore, holds potential for constructing a biophysical picture of the cellular environment. An important feature of any AP is its depolarization to threshold, termed the AP foot, which holds information about the origin of the AP. Currently, there exists no established technique for the quantification of the AP foot. In this study, we explore several possible approaches for this quantification, namely, exponential fitting, evaluation of the radius of curvature, triangulation altitude, and various area based methods. We have also proposed a modified area-based approach (CX,Y) which quantifies foot convexity as the area between the AP foot and a predefined line. We assess the robustness of the individual approaches over a wide variety of signals, mimicking AP diversity. The proposed (CX,Y) method is demonstrated to be superior to the other approaches, and we demonstrate its application on experimentally recorded AP profiles. The study reveals how the quantification of the AP foot could be related to the nature of the underlying synaptic activity and help shed light on biophysical features such as the density of innervation, proximity of varicosities, size of the syncytium, or the strength of intercellular coupling within the syncytium. The work presented here is directed toward exploring these aspects, with further potential toward clinical electrodiagnostics by providing a better understanding of whole-organ biophysics.

Commentary About the Biophysics of Muscles

This is a commentary about the biophysics of muscle, presenting an introduction to the area, modeling muscles' biophysics, and this Issue's projects.

Recent developments in the study of insect flight

Here we review recent contributions to the study of insect flight, in particular those brought about by advances in experimental techniques. We focus particularly on the following areas: wing flexibility and deformation, the physiology and biophysics of asynchronous insect flight muscle, the aerodynamics of flight, and stability and maneuverability. This recent research reveals the importance of wing flexibility to insect flight, provides a detailed model of how asynchronous flight muscle functions and how it may have evolved, synthesizes many recent studies of insect flight aerodynamics into a broad-reaching summary of unsteady flight aerodynamics, and highlights new insights into the sources of flight stability in insects. The focus on experimental techniques and recently developed apparatus shows how these advancements have occurred and point the way towards future experiments.

Subcutaneous and Intramuscular Hemodynamics and Oxygenation After Cold-Spray Application as Monitored by Near-Infrared Spectroscopy.

Vapocoolant spray, commonly known as cold spray (CS), is a cryotherapy modality used in sports medicine, athletic training, and rehabilitation settings. Proposed physiologic effects of cryotherapy modalities include reductions in tissue blood flow, oxygenation, and cell metabolism in addition to attenuation of pain perception attributed to reduced superficial nerve conduction velocity. To examine the effects of CS on subcutaneous and intramuscular blood flow and oxygenation on the thigh muscle using near-infrared spectroscopy, an optical method to monitor changes in tissue oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin. Cross-sectional study. Muscle Biophysics Laboratory. Participants were 13 healthy adults (8 men, 5 women; age = 37.4 ± 6 years, body mass index = 27.4 ± 2.6, adipose tissue thickness = 7.2 ± 1.8 mm). Conventional CS was applied to the vastus medialis muscles. Changes in chromophore concentrations of O2Hb, HHb, and tHb at superficial and deep layers were monitored for 5 minutes using a 2-channel near-infrared spectroscopy. Thirty seconds after CS application, we observed a decrease from baseline in O2Hb and tHb only in the superficial layer that was maintained for 3 minutes. Application of CS induced a transient change in blood flow and oxygenation of the superficial tissues with no change in deeper tissues over the healthy vastus medialis muscle. The limited physiologic effect of CS on the superficial hemodynamics and oxygenation of limb muscles may limit the therapeutic benefit of this cryotherapy modality to a temporary analgesic effect, a hypothesis that warrants a clinical trial on traumatized muscles.

A technique for simultaneous measurement of force and overlap between single muscle filaments of myosin and actin

In this study, we show a method for direct measurements of force and simultaneous visualization of isolated muscle filaments. Single actin filaments isolated from chicken skeletal muscle and single thick filaments isolated from Mussels were imaged using fluorescence and dark field microscopy, respectively. Force generated by the filaments was measured using micro-fabricated cantilevers. Force values were in the range observed previously with myosin filaments and molecules. The results suggest that the technique can be used to investigate many issues of interest and debate in the field of muscle biophysics.

Proteins, membranes and cells: the structure–function nexus—ASB 2008

While it is a common misconception that the laboratory is ‘a quiet garden of Eden’ for the introverted investigator it is nevertheless a stark diVerence from the hub-bub and buzz of a scientiWc meeting. The latter was also the case with the 32nd Annual Meeting of the Australian Society for Biophysics that took place at the Australian National University in Canberra from September 28th to October 1st, 2008. In an era when many national and international conferences are arranged by professional meeting organisers, held in purpose-built convention centres, and employ multiple parallel sessions, it is refreshing to attend a smaller conference where all the lectures are held in a single auditorium. This is particularly true when such a conference encompasses the breadth of research covered by Biophysics, as it aVords the opportunity to catch up with a lot of interesting ideas that one usually doesn’t have the time to think about in today’s busy schedules. The themes covered at the meeting that are reXected in the articles in this special edition, included Ion Channels, Fundamental Issues and Regulation of Membrane Transport, Protein Structure and Dynamics, Muscle Biophysics, Biophysical Characterisation Techniques, Plant Biophysics and Photosynthesis, Membrane Biophysics, General Biophysics, Cellular & Molecular Biophysics and Bioengineering, Biomolecules, Biomaterials and Biomimetics. The Wrst series of articles in this special issue are based on presentations given at a session held in memory of Professor Alexander (“Alex”) B. Hope and his work; Alex died in July 2008. He was one of the founders of biophysical research in Australia, so we were very fortunate that his Wrst two PhD students, Professors Hans Coster and Peter Barry, both of whom are still active members of the society, presented lectures of appreciation in the session, along with Dr. Fred Chow who worked with Alex Hope for the last 20 years of his extraordinarily productive life. Alex Hope spent a considerable time working on the giant cells of the alga, Chara; and his work did much to popularise this species as a model system for electrophysiological studies of isolated cells. Chara is in active use today as evidenced by, for example, the article by Dr. Mary Beilby and colleagues. Alex Hope’s work on the biophysics of membrane transport inspired generations of biophysicists in Australia and beyond; indeed biophysical studies of membrane transport has remained a strength of the Australian Biophysics community as is reXected in many of the articles in this special edition. A traditionally informative feature of meetings of the Australian Society for Biophysics (and of course others) is the Poster Sessions: All poster presenters are invited to speak for 90 s in the poster hall, to introduce their work and entice closer scrutiny during the main poster sessions. This has been a very eVective way of generating interest in the posters and stimulating questions and debate on site. We are also very pleased that 5 of the articles in this issue come from students; Asi Cohen (student oral prize winner), Sophia Goodchild (Poster prize winner), David Szekely (Poster prize winner), HanShen Tae and Karunasekara Yamuna. We hope that you the reader will Wnd, in the following pages, amongst the fruit of the ASB garden, much that is of interest and relevance to your own study and work, in the area of membranes, membrane proteins and the structural and functional connections between these macromolecules and multimolecular assemblies. J. I. Vandenberg (&) Department of Molecular Cardiology and Biophysics, Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, NSW 2010, Australia e-mail: j.vandenberg@victorchang.edu.au

Biophysical basis for airway hyperresponsivenessThis article is one of a selection of papers published in the Special Issue on Recent Advances in Asthma Research.

Airway hyperresponsiveness is the excessive narrowing of the airway lumen caused by stimuli that would cause little or no narrowing in the normal individual. It is one of the cardinal features of asthma, but its mechanisms remain unexplained. In asthma, the key end-effector of acute airway narrowing is contraction of the airway smooth muscle cell that is driven by myosin motors exerting their mechanical effects within an integrated cytoskeletal scaffolding. In just the past few years, however, our understanding of the rules that govern muscle biophysics has dramatically changed, as has their classical relationship to airway mechanics. It has become well established, for example, that muscle length is equilibrated dynamically rather than statically, and that in a dynamic setting nonclassical features of muscle biophysics come to the forefront, including unanticipated interactions between the muscle and its time-varying load, as well as the ability of the muscle cell to adapt (remodel) its internal microstructure rapidly in response to its ever-changing mechanical environment. Here, we consider some of these emerging concepts and, in particular, focus on structural remodeling of the airway smooth muscle cell as it relates to excessive airway narrowing in asthma.

Principles of Actuation in the Muscular System of Fish

Over the last 20 years, there have been tremendous intellectual and technological advancements in the fields of muscle biophysics, biomechanics, and musculoskeletal modeling. These advances have fueled a revolution in integrative muscle physiology. Whereas 20 years ago the notion of understanding the function and design of a muscular system from the molecular to the whole animal level was a dream, it is now becoming a reality. Fish represent an exceptional model for understanding the function and design of the muscular system of vertebrates. There are two fundamental reasons for this preeminence. First, the unique anatomical separation of the different muscle fiber types has made fish the most tractable model (i.e., the use and properties of the different muscle fiber types can be most easily studied). Second, fish utilize the broadest range of movement than any vertebrate. This diversity of movement imposes a wide array of challenges on the muscular system of fish and at the same time enables physiologists/biomechanists to observe how these challenges have been met. These features have permitted us to extract a number of general principles of actuation and control that have evolved over millions of years. Rather than summarizing the considerable literature on fish muscle function and fish swimming, this paper will focus narrowly on a relatively few studies that permit us to extract principles of actuation. These principles may in turn provide some insights into the design and construction of autonomous underwater vehicles (AUVs).

Jean Hanson – a woman to emulate: leading research into the molecular basis of contractility in muscle

In 1968 fresh from a Masters degree in theoretical physics, I was looking for a position and inspiration and Dr Mike Jacobs suggested I visit King’s College Biophysics Department in Drury Lane. It so happened that there was a vacancy for a post as Jean Hanson’s technician. After a discussion – hard to call it an interview – Jean said ‘I like you Miss Bennett’ and offered me the job. So I am part of Jean’s Legacy and I am very proud and pleased to be here today to give this talk. I would like to do two things in this talk. Firstly, to take an historical view of the development of Jean’s career, with particular emphasis on her comparative studies of other musclesthe smooth and invertebrate muscles – which led to our current view that there is a universal mechanism of muscle contraction. Secondly, to consider Jean’s qualities as a leader, in relation to the Muscle Biophysics Unit which she led from 1970–1973. (For a more detailed review of her life and work see the Biographical review by JT Randall, 1975) As Hugh said, Jean originally trained as a zoologist. She graduated with honours from Bedford College in 1941. I have had the pleasure recently of looking through her notebooks in the Archive at King’s College London http://www.kcl.ac.uk/depsta/iss/archives/collect/10ha70-1.html). Jean’s undergraduate notebooks are exemplary. I was struck by their neatness and the meticulous attention to detail in the diagrams in the dissection notebooks. After her degree she stayed at Bedford working as an assistant to Professor Harold Munro Fox, who was himself an eminent zoologist. He specialised in the circulation of marine invertebrates, especially the annelids. In 1947, she spent several months in Naples at the Marine Biology Station where she studied tube worms. She also visited the Marine Biology Laboratory at Plymouth and returned to Naples and Plymouth several times over the next 10 years. The papers she published of the morphology of the tube worms again demonstrate her exemplary draughtsmanship (For example, see Hanson, 1949). Throughout her notebooks of this period there are repeated references to the organisation of muscle in these creatures suggesting that even at that time she had developed an interest in muscle structure and function.

Bronchospasm and its biophysical basis in airway smooth muscle.

Airways hyperresponsiveness is a cardinal feature of asthma but remains unexplained. In asthma, the airway smooth muscle cell is the key end-effector of bronchospasm and acute airway narrowing, but in just the past five years our understanding of the relationship of responsiveness to muscle biophysics has dramatically changed. It has become well established, for example, that muscle length is equilibrated dynamically rather than statically, and that non-classical features of muscle biophysics come to the forefront, including unanticipated interactions between the muscle and its time-varying load, as well as the ability of the muscle cell to adapt rapidly to changes in its dynamic microenvironment. These newly discovered phenomena have been described empirically, but a mechanistic basis to explain them is only beginning to emerge.

Second International Symposium “Smooth Muscle Physiology and Biophysics”

The 2nd International Symposium on Smooth Muscle Physiology and Biophysics is organized jointly by the Bogomolets Institute of Physiology of the National Academy of Sciences of Ukraine (Kyiv, Ukraine), St. George’s Hospital Medical School of London University (Great Britain), and Taras Shevchenko National Kyiv University with support from the National Academy of Sciences of Ukraine, All-Ukraine Public Organization “Association of Pharmacologists of Ukraine,” The Wellcome Trust (Great Britain), and The Physiological Society (Great Britain). It will be held at the Bogomolets Institute of Physiology on October 28-31, 2003. The 1st Kyiv symposium “Smooth Muscle Physiology” was carried out 30 years ago in the tense international atmosphere of the cold war. However, many leading scientists were able to come from abroad, and the meeting seemed to open a window for cooperation between scientists from the USSR and their western colleagues. Today, the situation is entirely different, as many international research projects are conducted at the Bogomolets Institute, while Ukrainian scientists are performing research at universities throughout the world. The symposium will include lectures presented by prominent scientists from many countries on a wide range of smooth muscle physiology, biophysics, and pharmacology topics, including ionic mechanisms of electrical excitation, molecular organization, and biophysical properties of ion channels, neural regulation of smooth muscle motility, receptor-gated ion channels, mechanisms of action of neurotransmitters, calcium signals and active ion transport, excitationcontraction coupling, and mechanics of smooth muscle contraction. Twenty-five invited talks and short communications will be presented in seven sessions, namely: “Molecular Components of Cationic Channels: TRP and SOC,” “Neuronal Functions and Neurotransmitters,” “Endothelium and Smooth Muscle Function,” “Spontaneous Activity in Smooth Muscles,” “Responses of Smooth Muscle to Neurotransmitters,” “Regulation of Smooth Muscle Contraction,” and “Emerging Roles of Non-Smooth Muscle Cells in Smooth Muscle Tissues.” Two poster sessions, which will include about 50 research communications, are also planned. The program of the symposium will, thus, reflect the diversity of problems, techniques, and achievements of modern smooth muscle physiology and biophysics. We are hoping that the meeting will take place in a friendly and stimulating atmosphere of productive scientific exchange, which will enable young researchers to discuss problems and questions of modern smooth muscle physiology and biophysics with distinguished experts in this field. The Organizing Committee is happy to announce that the present symposium will coincide with the 75th birthday of Professor Mykhailo F. Shuba, who is one of the founders of contemporary smooth muscle physiology. We congratulate him on this event and wish Prof. Shuba good health and successful continuation of his important research.

Mechanochemical Coupling in Spin-Labeled, Active, Isometric Muscle

Observed effects of inorganic phosphate (P i) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin-catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force? Pate and Cooke (1989. Pflugers Arch. 414:73–81) showed that active, isometric muscle force varies logarithmically with [P i]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P i] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle.

Smooth Muscle Contraction: Recent Advances

Research in smooth muscle contraction has shown remarkable progress over the last 5 years. Striking advances have been made in the areas of biochemical regulation of contraction, centering on myosin light chain kinase activity, and of biophysical delineation of the contractile process at the actomyosin level by use of the newly developed motility assay. The purpose of the symposium held at Minaki, Ont., was to obtain a comprehensive reporting of the recent advances made in the area of smooth muscle contraction. Specifically, advances in the areas of biophysics of contraction, energetics, and contractile and regulator proteins (including the interesting newcomers caldesmon and calponin) and the changes that occur in pathophysiological entities such as asthma, hypertension, anaphylactic shock, high-altitude hypoxia, and persistent pulmonary hypertension of the newborn were presented.Key words: smooth muscle biophysics, smooth muscle biochemistry, energetics of smooth muscle, pathophysiology of smooth muscle.

Smooth Muscle Symposium

The 1991 CFBS Smooth Muscle Symposium, supported by Ciba-Geigy Canada, provided an opportunity to recognize Professor Edwin E. Danid's contribution to smooth muscle research. In a career spanning approximately forty years, Dr. Daniel's contributions are recognized worldwide and the CFBS symposium brought together some of Dr. Daniel's farmer graduate students and present colleagues and collaborators from North America. Dr. Daniel began h e symposium by providing a retrospective overview of Row, in his laboratory, smooth muscle research had developed. He highlighted the many contributions of those who had worked with him. Dr. Robert Garfield (McMaster University, and now Gdveston, Texas) followed with a review sf his own studies of the structure md function of gap junctions in smooth muscle. Dr. Nicholas Spereldcis (Cincinnati) then presented his findings concerning fast Na+ channels in uterine smooth muscle function. Dr. C. C. Y. (David) Kwan (McMaster) reviewed the development and use of subcellular membrane techniques for studies of smooth muscle function. The next speaker, Dr. Casey van Breemen of Miami, reviewed his recent studies of the regdation of @a2+ in vascular smooth muscle and stressed the impmnce of the superficial intracellular Ca2+ pool. The find speaker was Dr. Newman Stephens of Manitoba, who focussed on his studies relating the biochemistry and biophysics of smooth muscle to function. The symposium was cs-chaired by Dr. Michael W. Wolowyk of Edmonton and Dr. Christopher R. Triggle of Calgary. Both were graduate students in Edmonton when Dr. Daniel was chairman of the Department of Pharmacology at the University of Alberta. Dr. Wolowyk was one of Dr, Daniel's first PkD. students.