Motility is a fundamental property of living systems, from the cytoplasmic streaming of unicellular organisms to the most highly differentiated and devel oped contractile system of higher organisms, striated muscle. Research on var ious aspects of motile systems in muscle and undifferentiated or non muscle cells has been developing at an ever more rapid pace in the laboratories of investiga tors with a wide variety of backgrounds using methodologies varying from me chanics to the most sophisticated physical measurements. Significant contri butions to our understanding of motility are coming from the disciplines of cell biology, biochemistry, pharmacology, molecular biology, biophysics, and physiology. The findings have relevance not only to basic scientists but to clinicians in such diverse fields as cardiology and neurology and to scientists in the more traditional physical sciences. Cell and Muscle Motility is a new multivolume series of essays by distinguished research workers in various fields whose work has a common thread of dealing with one aspect or another of motility. The essays are meant to focus on topics of current interest, to be critical rather than exhaustive, and to indicate the current trends of research efforts. The series is intended to foster an interchange of concepts among various workers in the field and to serve as a reference for students and workers who wish to familiarize themselves with the most current progress in motility.

This volume intends to provide a comprehensive overview on the mecha nisms of muscle contraction and non-muscle cell motility at the molecu lar and cellular level, not only for investigators in these fields but also for general readers interested in these topics. A most attractive feature of various living organisms in the animal and plant kingdoms is their ability to move. In spite of a great diversity in the structure and function of various motile systems, it has frequently been assumed since the nineteenth century that all kinds of "motility" are essentially the same. Based on this assumption, some investigators in the nineteenth century thought that the mechanisms of motility could better be studied on primitive non-muscle motile systems such as amoeboid movement, rath er than on highly specialized muscle cells. Contrary to their expectation, however, the basic mechanisms of motility have been revealed solely by investigations on vertebrate skeletal muscles, since a monumental discovery of Szent-Gyorgyi and his coworkers in the early 1940s that muscle contraction results from the interaction between two different contractile proteins, actin and myosin, coupled with ATP hydrolysis.

The contributions to this volume were presented at a Symposium entitled "Current Topics in Muscle and Nonmuscle Motility" held in Dallas 19-21 November 1980 under the auspices of the A. Webb Roberts Center for Con tinuing Education, Baylor University Medical Center Dallas, and the Univer sity of Texas Health Science Center at Dallas. This very useful opportunity for a group of active investigators in motility to meet and discuss their latest findings was made possible in part by the income from an endowment fund established by a generous gift from Dr. Albert P. D'Errico in the Baylor University Medical Center. Dr. D'Errico was the first formally-trained neurosurgeon to practice in the Dallas area, the first Chief of Neurological Surgery, and a member of the Medical Board of the Baylor University Medi cal Center Dallas (1947 -1964). The income from this fund is used to promote the dissemination of up-to-date information in the Neurosciences, to provide intellectual stimulation, to add to the fund of knowledge, and improve the skills of neurosurgeons, neurologists, internists, and others in specialized fields of medicine. We are all indebted for this generous gift that made this enriching educational experience possible. We are also grateful for support the Symposium received from Electron Microscopy Sciences, Forma Scien tific, J. E. O. L. USA, Inc. , Ladd Research Industries, M. J. O. Diatome Co. , Or ganon Co. , Upjohn Co. , G. D. Searle & Co. , and Smith, Kline and French. Robert M.

Motility is a fundamental property of living systems, from the cytoplasmic streaming of unicellular organisms to the most highly differentiated and devel oped contractile system of higher organisms, striated muscle. Research on var ious aspects of motile systems in muscle and undifferentiated or non muscle cells has been developing at an ever more rapid pace in the laboratories of investiga tors with a wide variety of backgrounds using methodologies varying from me chanics to the most sophisticated physical measurements. Significant contri butions to our understanding of motility are coming from the disciplines of cell biology, biochemistry, pharmacology, molecular biology, biophysics, and physiology. The findings have relevance not only to basic scientists but to clinicians in such diverse fields as cardiology and neurology and to scientists in the more traditional physical sciences. Cell and Muscle Motility is a new multivolume series of essays by distinguished research workers in various fields whose work has a common thread of dealing with one aspect or another of motility. The essays are meant to focus on topics of current interest, to be critical rather than exhaustive, and to indicate the current trends of research efforts. The series is intended to foster an interchange of concepts among various workers in the field and to serve as a reference for students and workers who wish to familiarize themselves with the most current progress in motility.

Three distinct types of contractions perform colonic motility functions. Rhythmic phasic contractions (RPCs) cause slow net distal propulsion with extensive mixing/turning over. Infrequently occurring giant migrating contractions (GMCs) produce mass movements. Tonic contractions aid RPCs in their motor function. The spatiotemporal patterns of these contractions differ markedly. The amplitude and distance of propagation of a GMC are several-fold larger than those of an RPC. The enteric neurons and smooth muscle cells are the core regulators of all three types of contractions. The regulation of contractions by these mechanisms is modifiable by extrinsic factors: CNS, autonomic neurons, hormones, inflammatory mediators, and stress mediators. Only the GMCs produce descending inhibition, which accommodates the large bolus being propelled without increasing muscle tone. The strong compression of the colon wall generates afferent signals that are below nociceptive threshold in healthy subjects. However, these signals become nociceptive; if the amplitudes of GMCs increase, afferent nerves become hypersensitive, or descending inhibition is impaired. The GMCs also provide the force for rapid propulsion of feces and descending inhibition to relax the internal anal sphincter during defecation. The dysregulation of GMCs is a major factor in colonic motility disorders: irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and diverticular disease (DD). Frequent mass movements by GMCs cause diarrhea in diarrhea predominant IBS, IBD, and DD, while a decrease in the frequency of GMCs causes constipation. The GMCs generate the afferent signals for intermittent short-lived episodes of abdominal cramping in these disorders. Epigenetic dysregulation due to adverse events in early life is one of the major factors in generating the symptoms of IBS in adulthood.