A review of muscle transplantation in mammals.

Recent research in the field of mammalian muscle transplantation is reviewed with respect to the typical postoperative course of a free muscle graft. Several questions of clinical relevance are discussed, such as 1) whether or not predenervation of a muscle graft is necessary, 2) the issue of survival vs. regeneration of muscle fibres within the graft, and 3) whether or not a muscle must be grafted as an intact anatomical unit. In addition problems of neuromuscular relations are discussed.     

Force-interval relationship in heart muscle of mammals. A calcium compartment model.

A mathematical model was derived that describes peak force of contraction as a function of stimulus interval and stimulus number in terms of Ca2+ transport between three hypothetical Ca2+ compartments. It includes the conventional uptake and release compartments and recirculation of a fraction r of the activator Ca2+. Peak force is assumed to be proportional to the amount of activator Ca2+ released from the release compartment into the sarcoplasm. A new extension is a slow exchange of Ca2+ with the extracellular space via an exchange compartment. Six independent parameters were necessary to reproduce the different effects of postextrasystolic potentiation, frequency potentiation, and post-rest potentiation in isolated heart muscle from the rat. The normalized steady state peak force (F/Fmax) under standard conditions varied by a factor of ten between preparations from rat heart. Analysis with the model indicated that most of this variation was caused by two variables: the Ca2+ influx per excitation and the recirculating fraction of activator Ca2+. The influence of the Ca2+ antagonist nifedipine of the force-interval relationship was reproduced by the model. It is concluded that the model may serve to analyze the variability of contractile force and the mode of actions of drugs in heart muscle.     

The blood supply of muscle spindles in some mammals and the pigeon.

The blood supply of muscle spindles was studied in serial cross sections in macaque, cat, rabbit, guinea pig, mouse and pigeon muscles which had been incubated in a medium containing 3,3' diaminobenzidine. Lumina of blood vessels were recognized by the reaction product that was localized within erythrocytes. The outer capsule was well vascularized, but few or no capillaries were seen in the periaxial space. The inner spindle capsule, which closely invests the axial bundle, was rarely contacted by periaxial capillaries at the equator and juxtequator. Capillaries occurred more frequently adjacent to intrafusal fibers at the polar region and beyond the end of the outer capsule. Shorter diffusion distances and, usually, higher capillary densities were found at the polar region than at the spindle midsection. This suggests that transcapillary exchange at the polar segment is nearer to conditions prevalent in extrafusal muscle than elsewhere in the spindle, provided the inner and outer capsules are not less permeable at the poles than at the midsection. Differences in blood supply among mammalian species appear to be related to receptor size.     

Making more heart muscle

Postnatally, heart muscle cells almost completely lose their ability to divide, which makes their loss after trauma irreversible. Potential repair by cell grafting or mobilizing endogenous cells is of particular interest for possible treatments for heart disease, where the poor capacity for cardiomyocyte proliferation probably contributes to the irreversibility of heart failure. Knowledge of the molecular mechanisms that underly formation of heart muscle cells might provide opportunities to repair the diseased heart by induction of (trans) differentiation of endogenous or exogenous cells into heart muscle cells. We briefly review the molecular mechanisms involved in early development of the linear heart tube by differentiation of mesodermal cells into heart muscle cells. Because the initial heart tube does not comprise all the cardiac compartments present in the adult heart, heart muscle cells are added to the distal borders of the tube and within the tube. At both distal borders, mesodermal cell are recruited into the cardiac lineage and, within the heart tube, muscular septa are formed. In this review, the relative late additions of heart muscle cells to the linear heart tube are described and the potential underlying molecular mechanisms are discussed.     

Topography and structure of the stylohyoid muscle in mammals

Topography and structure of the musculus stylohyoideus (MSH) have been studied in 78 species of Mammalia from 12 orders. The muscle in question has specific peculiarities not only in its position and fixation, but also in a great variability of its structure. The MSH is not revealed in Philander opossum, Lagostrophus fasciatus, guinea pig, Meriones eversmanni, Rhombomys opimus, Nyctereutes procyonoides, Thos aureus, Mastelidae. Various pathways of development and different functional loading define existence of several modifications of the MSH: a) the medial part of the muscle develops (Didelphys, Rodentia, Insectivora, Proboscidea, Dama dama, Capreolus capreolus; b) the lateral part of the musculus develops (Lagomorpha, Canis lupus, Ursidae, Felidae, Pinnipedia, Cavicornia); c) both parts of the musculus develop, determining position of the m. digastricus between these two parts (Alces alces, Pseudaxis sica, Cervus elaphus, Macaca rhesus, Erythrocebus patas, Perissodastyla).     

Proprioceptive innervation of the external cremaster muscle of some domestic mammals.

The proprioceptive innervation of the external cremaster muscle of some domestic animals was studied. Muscle spindles and tendon organs with their well-known features were found, but this finding was uncommon and unexpected in the investigated animals. For this reason, we believe that there is no relationship between the presence of these proprioceptors and the cremasteric reflex.     

Location of the vector of jaw muscle force in mammals

Previous work has suggested that the third molar lies just in front of the point where the resultant vector of jaw muscle force, estimated from dissections, intersects the tooth row. This point meets the jaw such that the vector is 30% of jaw length from the jaw joint. Thus, the vector divides the jaw in the ratio of 3:7 when measurements are taken perpendicular to the vector. In practice, however, distances along mammalian jaws are typically measured on an easily determined line such as a line from one end of the tooth row to the other. The position of the jaw joint is then projected onto this line. As a rule, such a line is not perpendicular to the vector and so the distance from the projection of the joint, out to the rear of the third molar (and the vector's intersection), is different in different mammals. Rarely is this distance 30% of total jaw length. However, when the location of the vector's intersection is measured along the tooth row, this position varies directly with the inclination of the vector; a vector inclined posteriorly intersects the tooth row far from the projection of the joint and an anterior vector's intersection is relatively close. Only a vector perpendicular to the line from one end of the tooth row to the other intersects at 30%. This obvious point suggests a way to test the above hypotheses when the inclination of the vector is not known exactly. The predicted relationship between the distance to the molar, as a percentage of the total jaw length, and the approximate inclination of the vector derived from muscle weights (posterior or anterior depending on whether the temporalis or the masseter/pterygoid, respectively, is dominant) was observed in a sample of 46 different mammals.     

Comparative levels of muscle glycolytic enzymes in mammals, fish, echinoderm and molluscs.

1. Levels of glycolytic enzymes were determined in terms of units of enzyme/mg protein in rat striated muscle, carp lateral muscle, holothuria longitudinal muscle of the body wall, and a snail foot muscle. 2. An attempt has been made to correlate levels of glycolytic enzymes as a parameter to establish a "biochemical distance" at molecular level and correlate this with the phylogenetic position in animals sufficiently separated in the animal tree of evolution. 3. The possibility of a peculiar kinetic behaviour of the glycolytic pathway in each muscle tissue studied, has been analyzed as the profiles of the ratios of pairs of enzymes bearing a substrate-product dependence. 4. A possible "futile synthesis" of some glycolytic enzymes, such as FDP-aldolase in the case of fish muscle, is proposed.