Understanding the mechanisms of lung mechanical stress

Physical forces affect both the function and phenotype of cells in the lung. Bronchial, alveolar, and other parenchymal cells, as well as fibroblasts and macrophages, are normally subjected to a variety of passive and active mechanical forces associated with lung inflation and vascular perfusion as a result of the dynamic nature of lung function. These forces include changes in stress (force per unit area) or strain (any forced change in length in relation to the initial length) and shear stress (the stress component parallel to a given surface). The responses of cells to mechanical forces are the result of the cell's ability to sense and transduce these stimuli into intracellular signaling pathways able to communicate the information to its interior. This review will focus on the modulation of intracellular pathways by lung mechanical forces and the intercellular signaling. A better understanding of the mechanisms by which lung cells transduce physical forces into biochemical and biological signals is of key importance for identifying targets for the treatment and prevention of physical force-related disorders.

Evaluación morfologia de las uniones intercellulares en el ovario del embrión de pollo: acción de hormonas esteroideas y gonadotroficas in vitro / Morphological evaluation of intercellular junctions in the ovary of chick embryos: action of steroid and gonadotropic hormones in vitro

Se determinaron las variaciones de las uniones intercelulares de las células germinales y epiteliales en el epitelio ovárico producidas por hormonas gonadotróficas y esteroideas sobrelos ovarios del embrión de pollo a los 7 días de desarollo. Se cultivaron explantos de ovarios derecho e izquierdo Sin (controles) y con adición de hormonas (experimental durante 4 días. Los cultivos fueron procesados para su estudio ultraestructural (MET). En ambos ovarios controles los complejos de unión eran similares a los identificados in ovo. En el ovario izquierdo se observó aumento y mayor desarollo de las uniones adherens y desmosomas; en el ovario derecho los mismos disminuyeron por acción de 17 Beta-estradiol. La respuesta del ovario izquierdo a la progesterona y testoterona fue similar a la obtida con estrógeno. En la gónada derecha no se observaron cambios. En ambos ovarios se produjo una dismunucíon de las uniones intercelulares por accíon de FSH. Los cambios producidos por LH y hCG fueron semejantes a los encontrados en el ovario izquierdo por efecto del estrógeno, consistentes en un incremento de los complejos de uníon, principalmente los de tipo adherens. Estos análisis indican que las hormonas esteroideas y gonadotróficas actúan modificando las uniones intercelulares y participarían en los procesos de crecimiento y atrofia que ocurren en los ovarios del embríon de pollo.

Properties of channels from rat liver gap junction membrane fractions incorporated into planar lipid bilayers

Rat membrane fractions highly enriched for gap junctions can be incorporated into planar lipid bilayers exhibiting channel currents with both voltage-dependent and independent components. Voltage dependence, however, is only one of the characteristics of liver gap junction channels. Other features include poor ionic selectivity and sensitivity to calcium, pH, octanol and to some intracellularly applied antibodies. To further test the junctional nature of channels from membrane fractions highly enriched in gap junctions incorporated into lipid bilayers we studied the sensitivity of these channels to uncoupling agents and determined channel selectivity properties. We found the incorporated channels to be insensitive to calcium and octanol, and in most cases to pH in the range of 5-7, suggesting that either these agents do not interact directly with the junctional channels or that the corresponding gating regions are inactivated during the isolation and reconstitution procedures. Attempts to block channel activity using polyclonal and monoclonal connexin 32 antibodies were generally unsuccessful, although one antibody (a monoclonal directed against the carboxy terminus portion of connexin32) blocked channel activity. Selectivity measurements indicated that the incorporated channels were slightly cation selective (PNa=Pk > PCl) and were permeable to large ions. These results further support the idea that functional connexin32 gap junction channels are present in channel activity recorded from rat liver junctional membranes incorporated into planar bilayers

Complex channel activity recorded from rat liver GAP junctional membranes incorporated into lipid bilayers

Channels from isolated liver junctional membranes were incorporated into lipid bilayers and studied under voltage clamp conditions. Detergent treatment of junctional membrane fragments greatly increased the incidence of channel incorporation but did not noticeably alter the properties of the incorporated channels. Incorporation resulted in channel activity displaying an approximately symmetric voltage dependence in which conductance was decrease with imposed transmembrane voltage exceeding ñ 20 mV. A residual coltage-independent conductance was also detected in membranes in which liver junctional membranes were incorporated. The magnitude of this voltage-insensitive component varied from less than 20% to more than 75% of the total conductance. These results are generally similar to those described by Young, Chn and Gilula(Cell, 48:733-743, 1987) in incorporation experiments following detergent treatment of isolated gap junction membranes. However, we interpret these data as indicating the existence of distint channel populations in the incorporated membrane fractions. Our results suggest that a population of larger conductance channels (* 150 pS) contributes the voltage-dependent component of the membrane conductance, while smailler channels (unitary conductance abouth 50-150 pS) contribute the voltage-independent component. The biophysical proprieties of the larger channel are comparable to those seen in communication-deficient cells transfected with connexin32, confirming a report describing conductance of bilayers in which electroeluted 27-kDa liver gap junction protein was inserted. These findings indicate that connexin32 comprises the larger, voltage-dependent channels seen in the bilayer experiments in which liver junctional membranes are incorporated

The internal horizontal cell of the frog: spatial summation

En la Rana pipiens se estudiaron las propiedades del campo receptivo de las células horizontales internas (CHI). Se determinó la constante de espacio de cada célula usando puntos luminosos de diferentes tamaños o moviendo una abertura luminosa rectangular a lo largo de la retina. Con el primer método, la constante varió entre 100 - 500 um y con el segundo, entre 100 - 720 um. Se describió un rango de valores similar en el Xenopus, aunque sus SHI son más grandes que las de la Rana. Aparentemente, el acoplamiento entre las CHI es más eficiente en la retina de la Rana que en aquellá del Xenopus. El amplio rango de los valores sugiere que entre las células de la misma retina hay una variación importante en la eficiencia del acoplamiento