Biochemical and ultrastructural aspects of Mr 165,000 M-protein in cross-striated chicken muscle.

To better understand the relationship between the Mr 165,000 M-line protein (M-protein) and H-zone structure in skeletal and in cardiac muscle, as well as the possible interaction of M-protein with another skeletal muscle M-line component, the homodimeric creatine kinase isoenzyme composed of two M subunits (MM-CK), we performed biochemical, immunological, and ultrastructural studies on myofibrils extracted by different procedures. In contrast to MM-CK, M-protein could not be completely removed from myofibrils by low ionic strength extraction. Fab-fragments of antibodies against M-protein could not release M-protein quantitatively from either breast or heart myofibrils but remained bound to the myofibrillar structure, whereas monovalent antibodies against MM-CK cause the specific release of MM-CK and the concomitant disappearance of the M-line from chicken skeletal muscle myofibrils. When MM-CK was removed from skeletal myofibrils by low ionic strength extraction or, more specifically, by incubation with anti-MM-CK Fab, M-protein was still not released quantitatively upon treatment with anti-M-protein Fab as judged from immunofluorescence data. In the ultrastructural investigation of low ionic strength extracted muscle fibers, M protein could be localized in two stripes on both sides of the former M-line, suggesting a reduced attachment to the residual H-zone structure, whereas the specific removal of MM-CK resulted in the same dense staining pattern for M-protein within the M-line as observed in untreated fibers. However, the binding of M-protein to the residual M-line structure seemed to be reduced, as a considerable amount of this protein could be identified in the supernate of sequentially incubated myofibrils. The results indicate a strong binding of M-protein within the H-zone structure of skeletal as well as heart myofibrils.

Monovalent antibodies against MM-creatine kinase remove the M line from myofibrils.

Column-purified antibodies against creatine kinase (EC 2.7.3.2) from chicken skeletal muscle (the homodimeric isoenzyme designated MM-CK) bind specifically to the M lines of chicken pectoral muscle myofibrils. Incubation of myofibrils with monovalent Fab' fragments of these antibodies solubilizes most of the myofibril-bound creatine kinase, concomitantly removing most of the electron-dense material from the M lines. This strongly indicates that MM-CK is an integral part of the M-line structure and is consistent with the suggestion that MM-CK molecules form the M bridges that are responsible for the principle M-line substriations.

Localization of creatine kinase isoenzymes in myofibrils. II. Chicken heart muscle.

Chicken heart muscle contains almost exclusively the BB isoenzyme of creatine kinase (CK), its myofibrils, moreover, lack an M-line. This tissue thus provides an interesting contrast to skeletal muscle, in which some of the MM-CK present as predominant CK isoenzyme is bound at the myofibrillar M-line. Approx. 2% of the total CK activity in a chicken heart homogenate remains bound to the myofibrillar fraction after repeated washing cycles; both the fraction and the absolute amount of CK bound are about threefold lower than in skeletal muscle. Almost all of the bound enzyme is located within the Z-line region of each sarcomere, as revealed by indirect fluorescent-antibody staining with antiserum against purified chicken BB-CK. After incubation with exogenous purified MM-CK, positive immunofluorescent staining for M-type CK at the H-region of heart myofibrils was observed, along with weaker fluorescence in the Z-line region. Chicken heart myofibrils may thus possess binding sites for both M and B forms of CK.

[Electrophysiologic semiology of daytime sleep in 7 to 9-year-old children]. / Semeiologie électrophysiologique du sommeil de jour chez l'enfant de 7 a 9 ans

The afternoon sleep of 12 children aged 7-9 was studied; its electrophysiological indices and sequential organization were described and compared to those of afternoon sleep of adults and to those of night sleep of adults and children. The EEG indices which differentiate sleep patterns of children from adults' were the following: abundance of slow rhythms from onset of sleep; absence of low voltage fast activity at sleep onset and during REM sleep; early appearance of a large amount of transitory potentials in the form of sharp rolandic waves and sharp occipital waves. Moreover, either focal or generalized paroxysmal discharges occasionally occurred. Even when it covers a complete sleep cycle, the afternoon sleep of children appears shorter than both that of adults and the first cycle of night sleep in children of the same age. The organization of sleep components does not allow identification of the classical stages defined in adults nor to describe homogeneous stages which are specific to children. The very atypical character of REM sleep also makes it difficult to differentiate unequivocally the classical slow and paradoxical sleeps. The significance of rolandic and occipital sharp transients is discussed; the role of maturation and the influence of the time of occurrence within the circadian rhythm are considered, in order to explain the phenomenological and temporal characteristics of day sleep in children.