The development of Purkinje fibres and ordinary myocytes in the bovine fetal heart

Summary A comparative ultrastructural study of bovine Purkinje fibres and ordinary myocytes during fetal development has been undertaken. Differences between the two cell types with respect to the intercalated disc, amount of myofibrils, arrangement of mitochondria, amount of glycogen and formation of T-tubules became apparent gradually. In all stages studied an abundance of intermediate filaments was typical for the Purkinje fibres. Myofibrillar M-bands developed at an earlier stage in Purkinje fibres than in ordinary myocytes. Myofilament-polyribosome complexes typical of adult cow Purkinje fibres were not observed in the fetal hearts. Only in late fetal stages were leptofibrils observed in both cell types.We conclude that in the bovine heart Purkinje fibres develop along a different pathway from ordinary myocytes.This study was supported by grants from the Swedish Medical Research Council (12X-3934), the Faculty of Medicine, University of Umeå, and the Expressen Prenatal Fund     

Morphological changes observed in rats immunized with the Torpedo acetylcholine receptor α-chain

Lewis rats were immunized with nicotinic acetylcholine receptor (nAChR) polypeptides purified from the electric tissue of Torpedo marmorata. Animals immunized with the acetylcholine binding, 41.500 daltons, polypeptide showed comparable fragmentation of the postsynaptic membrane and indications of rearrangement of the adjacent muscle fiber as earlier found in rabbits and rats immunized with the nAChR complex. Thus, these results demonstrate that the α-polypeptide chain carries all determinants necessary for onset of Experimental Autoimmune Myasthenia Gravis (EAMG).     

Differentiation of fibres in human masseter, temporal and biceps brachii muscles. A histochemical study.

Masseter, temporal and biceps brachii muscles were histochemically evaluated for fibre type differentiation on 19 aborted fetuses (gestational ages 15-23 weeks), in 2 premature infants of 34 and 36 weeks gestation and in 2 fullterm stillborn infants. There was no convincing evidence of fibre type differentiation in the masticatory muscles before 22 weeks' gestation while a fairly distinct differentiation was seen in biceps brachii specimens at 16 weeks' gestation with ATPase at pH 4.35. Around 22 weeks two types of fibre were found in all specimens with ATPase at pH 4.35. With regular ATPase (pH 9.4) there was a relatively weak difference in staining between different types of fibre in the masticatory muscles. In biceps brachii Type I and Type II were demonstrated. Neonatally 3 levels of staining were seen in biceps brachii with regular ATPase (pH 9.4); while ATPase pH 4.35 and 4.6 demonstrated the subtypes IIB and IIC. In the masticatory mucles only 2 levels were recognized with regular ATPase and all type II fibres had the characteristics of Type IIC as seen with with ATPase at pH 4.35.     

Histochemical fibre composition of the human digastric muscle

The histochemical muscle-fibre composition of the anterior and posterior belly of the human digastric muscle was analysed in young male adults. Both bellies, of differing embryological origin and supplied by different cranial nerves, showed a fibre composition similar to that of normal limb and trunk muscles. Type I, type IIA and type IIB fibres each occupied about one-third of the total fibre population and were evenly distributed in a mosaic pattern. About 1 per cent of fibres were type IIC and ATPase (pH 9.4) intermediate fibres. Thus, there were major differences between the anterior belly of digastric and the likewise trigeminal nerve innervated masticatory muscles with respect to both histochemical profile and size and distribution of various types of fibre. The observations suggest that the fibre pattern of the digastric is not primarily related to its specific nervous supply but its special functional demands. The predominance of type II fibres indicates a capacity for fast acceleration and speed in mandibular movements. The disparity in fibre-type profile between the digastric and the jaw elevator muscles might be related to changing demands during evolution. Civilized diets need no heavy mastication and, while the requirements upon the jaw elevators have thus changed, the functional demands on the jaw openers would have remained unchanged.     

A new type of hereditary distal myopathy with characteristic sarcoplasmic bodies and intermediate (skeletin) filaments

A family with a hitherto unrecognized type of distal myopathy is described. The disorder appears to be of late onset and to be inherited through a dominant autosome. It has a more malignant course than the distal myopathies described earlier, from which it can be differentiated clinically by an early involvement of thenar muscles and hand flexors. The key to the correct diagnosis is provided by the morphological and immunohistological investigation of muscle biopsies, which show typical sarcoplasmic bodies and an abundance of intermediate-sized (skeletin) filaments.     

Intermediate filament proteins in developing human arteries

 The distribution of intermediate filament proteins in adult human blood vessels and in human fetal elastic arteries is relatively well-known. However, the distribution of these proteins in the course from neonate to adult has not been established. In this investigation, human postnatal arteries were studied with immunohistochemistry, using antibodies targeted on the intermediate filament proteins desmin, vimentin and cytokeratins 8, 18 and 19. Vimentin was present in most smooth muscle cells in all vessels and at all ages. The proportions of desmin-expressing cells increased in the elastic arteries during the first year of life and was higher in the pulmonary trunk than in the aorta. In the muscular arteries, the proportion of desmin-labelled cells increased in the coronary and the deep femoral arteries, but remained constant in the renal and the cerebral arteries. Cytokeratins were detected in the pulmonary trunk earlier than in the aorta. Cytokeratins were present throughout the wall of the ductus arteriosus, but desmin was present only in some cells. Thus, there are postnatal changes in the distribution of intermediate filament proteins in the elastic arteries and in some muscular arteries, whereas the intermediate filament pattern remains unchanged in other muscular arteries. Accepted: 31 July 1998     

Variation in histochemical enzyme profile and diameter along human masseter intrafusal muscle fibers

The histochemical enzyme profile of human masseter intrafusal muscle fibers was analyzed in consecutive serial cross sections along the individual fibers. Two hundred intrafusal fibers in 21 muscle spindles were classified. On the basis of equatorial nucleation, myosin ATPase-staining reactions after alkaline and acid preincubations and diameter, four different populations or types of intrafusal fiber were identified: large-diameter alkaline-stable and acid-stable fibers, bag2; two types of fiber with intermediate-diameter, alkaline-labile and acid-labile fibers corresponding to bag1 and alkaline-labile and acid-stable fibers designated as AS-bag1; and small-diameter alkaline-stable and acid-stable (pH 4.6)-acid-labile (pH 4.3) fibers called chain fibers. Regional variability in staining and diameter along the individual fibers was noted. In general, intrafusal fibers showed stronger oxidative reactions than did extrafusal fibers. The enzyme profile of the human masseter intrafusal fibers differed from that of extrafusal fibers in jaw, limb, and trunk muscles and also from that reported for spindles in limb and trunk muscles in man. The result suggests unique properties of human jaw muscle spindles and the jaw motor system.