Aging impairs Ca2+ sensitization pathways in gallbladder smooth muscle.

Calcium sensitization is an important physiological process in agonist-induced contraction of smooth muscle. In brief, calcium sensitization is a pathway that leads to smooth muscle contraction independently of changes in [Ca(2+)](i) by mean of inhibition of myosin light chain phosphatase. Aging has negative impacts on gallbladder contractile response due to partial impairment in calcium signaling and alterations in the contractile machinery. However, information regarding aging-induced alterations in calcium sensitization is scanty. We hypothesized that the calcium sensitization system is negatively affected by age. To investigate this, gallbladders were collected from adult (4 months old) and aged (22-24 months old) guinea pigs. To evaluate the contribution of calcium sensitization pathways we assayed the effect of the specific inhibitors Y-27632 and GF109203X on the "in vitro" isometric gallbladder contractions induced by agonist challenges. In addition, expression and phosphorylation (as activation index) of proteins participating in the calcium sensitization pathways were quantified by Western blotting. Aging reduced bethanechol- and cholecystokinin-evoked contractions, an effect associated with a reduction in MLC20 phosphorylation and in the effects of both Y-27632 and GF109203X. In addition, there was a drop in ROCK I, ROCK II, MYPT-1 and PKC expression and in the activation/phosphorylation of MYPT-1, PKC and CPI-17 in response to agonists. Interestingly, melatonin treatment for 4 weeks restored gallbladder contractile responses due to re-establishment of calcium sensitization pathways. These results demonstrate that age-related gallbladder hypocontractility is associated to alterations of calcium sensitization pathways and that melatonin treatment exerts beneficial effects in the recovery of gallbladder contractility.

The persistence of bacterial and methanogenic archaeal communities residing in the rumen of young lambs.

The aim of this experiment was to study the persistence in time of bacterial and methanogenic archaeal communities that establish in the rumen of lambs fed two different diets at weaning. Twenty ewes with single lambs were used in two phases. In phase I, 10 lambs had access only to grass hay (H group). The other 10 lambs had free access to concentrate and grass hay (C group). After 20 weeks, five lambs from each group were slaughtered and rumen samples were kept for analysis. In phase II, the remaining lambs were grouped together and fed grass plus concentrate for 4 months and then slaughtered, and rumen samples were collected for analysis. Terminal restriction fragment length polymorphism analysis showed a different bacterial and methanogen population established in the rumen of H and C lambs in phase I. These differences disappeared for methanogens after both groups were fed the same diet for 4 months; however, the total bacterial community remained different for the H and C samples. Our results suggest that some of the differences in the microbial populations that establish in animals fed different diets at weaning persist in the long term, which provides the possibility of programming the microbial populations in the adult animal.

Developmental changes in Ca2+ homeostasis and contractility in gallbladder smooth muscle.

Relatively little is known about the contribution of Ca(2+)-dependent and -independent mechanisms in the contractility of neonatal gastrointestinal smooth muscle. We therefore studied Ca(2+) homeostasis and Ca(2+) sensitization mechanisms in 10-day-old and adult guinea pig gallbladder smooth muscle to elucidate developmental changes in these processes. Gallbladder contractility was evaluated by isometrical tension recordings from strips, intracellular Ca(2+) concentration was estimated by epifluorescence microscopy of fura-2-loaded isolated cells, and protein expression and phosphorylation were assessed by Western blot analysis. The neonatal gallbladder contracted significantly less to CCK than adult tissue, but this correlated with an increased Ca(2+) mobilization, suggesting immaturity of Ca(2+) sensitization mechanisms. The enhanced Ca(2+) release in the newborn gallbladder was the result of the increase in the size of the releasable Ca(2+) pool. Moreover, in neonatal smooth muscle cells, neither the plasma membrane Ca(2+) pump nor the Na(+)/Ca(2+) exchanger collaborate in the extrusion of Ca(2+). In contrast, in these cells, there is an increase in phospholamban phosphorylation, which could drive to an overactivity of the sarco(endo)plasmic reticulum Ca(2+)-ATPase pump. The reduced Ca(2+) sensitivity in neonatal tissues was demonstrated by the lack of effect to Y-27362, an inhibitor of Rho kinase (ROCK), and GF-109203X, an inhibitor of PKC, on agonist-induced contraction. In addition, the neonatal gallbladder showed lower levels of RhoA, ROCK, PKC, and two effectors [C-kinase-dependent inhibitor of 17 kDa (CPI-17) and myosin phosphatase targetting 1 (MYPT1)] as well as an absence of CPI-17 and MYPT1 phosphorylation in response to agonists. In conclusion, our results indicate that the main mechanisms involved in smooth muscle contractility are under developmental regulation.

Mujer, crecimiento económico y equidad social / Woman, economic growth and social equity

El presente documento aborda la situación de la mujer en los campos del crecimiento económico y la equidad social y se divide en los siguientes capítulos: I. Introducción II. Situación económica de México durante el periodo 1980-1995 III. Principales programas enfocados a la mujer (1980-1995) IV. Equidad social y equidad de género V. Conclusiones y propuestas.