1,721,006 research outputs found
CHANGES IN MEMBRANE IONIC CONDUCTANCES AND EXCITABILITY CHARACTERISTICS OF RAT SKELETAL MUSCLE DURING AGING
No full textMembrane electrical properties, component ionic conductances and excitability characteristics of extensor digitorum longus muscle from 3-4, 16 and 29 months old rats were measured "in vitro". Fiber diameter, membrane resistance (Rm) and membrane capacitance, increased with aging, and the increase was significant at 29 months. The increase of Rm was mostly due to a decrease of chloride conductance (GC1), whereas potassium conductance (GK) increased only slightly, at 16 and 29 months. Due to the lowered GC1, the latency of action potential increased at both ages with a consequent prolongation of the duration of action potential. Nevertheless, a decrease in the firing capability was recorded in the aged fibers. Our results indicate, that during aging, the most affected parameter of skeletal muscle fibers is GC1, although changes of this passive conductance alone cannot entirely account for the changes in the excitability characteristics recorded
Membrane ionic conductances in normal and denervated skeletal muscle of the rat during development
No full textThe development of membrane ionic conductances of rat extensor digitorum longus (EDL) muscle fibers was studied in vitro using intracellular recordings. At 7-8 days after birth, the potassium conductance (GK) dominated the total membrane conductance while the chloride conductance (GCl) was very low. A rapid increase of GCl towards adult values was observed after few days (12-14 day old rats), whereas GK did not decrease up to day 23. Denervation at 7-8 days after birth suppressed the maturation of the electrical parameters measured, and 15 days after the nerve crush, GCl was just detectable. These results suggest that the maturation of the electrical properties, and in particular that of the resting chloride conductance in mammalian striated muscle fibers, occurs during the first weeks of postnatal life and is dependent on innervation
THE INFLUENCE OF INACTIVITY ON MEMBRANE RESTING CONDUCTANCES OF RAT SKELETAL MUSCLE FIBERS UNDERGOING REINNERVATION.
No full textThe role of activity in the maintenance of the normal component resting conductances of skeletal muscle fibres has been evaluated in vitro in rat extensor digitorum longus muscle during reinnervation from 2 to 40 days (a) after crushing of the peroneus nerve and (b) after local application of tetrodotoxin (TTX) to the crushed nerve. Whereas membrane conductances were regained after crushing alone, they were not completely restored when impulse propagation was blocked with TTX. It is concluded that nerve trophic factors are of primary importance in the control of muscular membrane conductances, and that transmission at the endplate and the muscle usage triggered by it have a minor but significant effec
EFFECTS OF CHLORIDE CHANNEL STEREOSPECIFIC ACTIVATOR AND INHIBITOR ON MYOTONIC MOUSE SKELETAL-MUSCLE FIBERS
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
The effect of diphenylamine-2-carboxylate on C1- channel conductance and on excitability characteristics of rat skeletal muscle
No full textThe effect of diphenylamine-2-carboxylate (DPC), a blocker of the Cl- conductance pathway in Cl- transporting epithelia, has been evaluated in-vitro on the electrophysiological variables of rat extensor digitorum longus muscle fibres. DPC (5-240 μM) caused a dose-related increase of membrane resistance which was attributed entirely to a fall in Cl- channel conductance (IC50, 120 μM), since potassium conductance was not affected by the treatment. DPC also modified fibre excitability. A significant dose-dependent increase was observed in the latency of the action potential and in the excitability of the membrane. DPC was less potent on striated fibres than anthracene-9-carboxylic acid, another specific blocker of C1- channel conductance. Moreover DPC was less potent on skeletal muscle than on C1- transporting epithelia. Morphological differences in the Cl- channels or of the drug binding sites may account for the differences between tissues
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