Browsing by Author "MALDONADO, M"

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    ADAPTIVE REGULATION OF HEPATIC BILE-SALT TRANSPORT - EFFECT OF PROLONGED BILE-SALT DEPLETION IN THE RAT
    (1988) ACCATINO, L; HONO, J; MALDONADO, M; ICARTE, MA; PERSICO, R
    Exposure of the liver to increased bile salt flux can increase the bile salt maximum secretory rate (SRm), presumably through the induction of new transport sites. The converse, i.e., the down-regulation of SRm upon bile salt deprivation, has not been demonstrated. We examined the effects of bile salt depletion for 24 h and 48 h on taurocholate SRm and bromsulphalein (BSP) SRm, and on [14C]taurocholate binding to isolated liver surface membranes in unrestrained external biliary fistula rats. Taurocholate SRm was significantly decreased by 35% and 51% in 24-h-depleted and 48-h-depleted rats, respectively, compared with control, sham-operated rats. Maximal taurocholate concentration in bile was also significantly lower in the bile-salt-deprived rats. In contrast, BSP SRm was not significantly different between depleted animals and controls. Bile salt depletion for 24 h and 48 h did not significantly alter liver surface membrane protein recovery and membrance enzyme specific activity including Na+ + K+-ATPase. Specific[14C] taurocholate binding to liver surface membranes was significantly decreased by 25% in 24-h-depleted rats compared with control rats. In contrast to taurocholate SRm, bile salt depletion for 48 h did not result in further reduction of specific taurocholate binding sites. This study demonstrates that taurocholate SRm progressively decreased in 24-h- and 48-h-bile salt-depleted rats, this being consistent with adaptive down-regulation of hepatic bile salt transport. This effect is selective, since BSP SRm was unaltered. The depressed taurocholate SRm can be explained at least in part by decreased bile salt receptor density in liver surface membranes. It appears to be unrelated to either a reduction in membrane surface area (membrane protein recovery and enzyme activity were unchanged in bile salt-depleted rats) or altered Na+ electrochemical gradients (Na+ + K+-ATPase activity was not significantly different between bile salt-depleted and control rats).
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    AGE-RELATED RESPONSES OF SKELETAL-MUSCLE AFTER ECTOPIC INNERVATION, WITH PARTICULAR REFERENCE TO 16S ACETYLCHOLINESTERASE, IN ADULT-RATS
    (1984) MALDONADO, M; RAMIREZ, BU; RUIZ, G; YAMUY, J; INESTROSA, NC
    The formation of ectopic junctions between the foreign fibular nerve and the soleus muscle of young (35-day-old) and mature (200-day-old) adult rats was induced by severing the normal nerve 4 wk after implanting the foreign nerve. The various molecular forms of acetylcholinesterase (AChE) were studied both at the implanted region and at the original denervated endplates. The velocity of contraction was also studied. In young rats the 16S form was first detected in the ectopic junctions around day 5 after reinnervation; this form rapidly increased during the following weeks, reaching a plateau by day 20. By contrast, in mature rats the appearance of the 16S AChE was dramatically delayed; in fact, it could not be observed before day 80 after reinnervation. (The 16S AChE form appeared at day 20 after reinnervation in the original denervated endplates of young rats; however, at the same time, no effect was observed in mature animals.) The original, slow muscle fibers of the soleus became faster upon reinnervation; this change also occurred much earlier in younger than in mature rats. A loss of plasticity in the skeletal muscle of mature rats is indicated. Caution is suggested in the use of the ectopic innervation model to study development in mature adult rats.
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    THE ELECTRIC ORGAN OF DISCOPYGE-TSCHUDII - ITS INNERVATED FACE AND THE BIOLOGY OF ACETYLCHOLINESTERASE
    (1984) MENDEZ, B; GARRIDO, J; MALDONADO, M; JAKSIC, FM; INESTROSA, NC
    An ultrastructural, histochemical and biochemical study of the electric organ of the South American Torpedinid ray. D. tschudii was carried out. Fine structural cytochemical localization of acetylcholinesterase (AChE) indicated that most of the esterase was associated with the basal lamina. EM indicated no marked differences in the electrocyte ultrastructure between Discopyge and Torpedo californica. Discopyge electric organ possessed 3 molecular forms, 2 asymmetric forms (16 S and 13 S) and 1 globular hydrophobic form (6.5 S). The asymmetric 16 S AChE form was solubilized by heparin, a sulfated glycosaminoglycan, suggesting that heparin-like macromolecules are involved in the binding of the enzyme to the basal lamina. Cell-free translated AChE peptides, synthesized using Discopyge electric organ poly(A+) RNA, correspond to a main band of 62,000 daltons which probably represents the catalytic subunit of the asymmetric AChE.