PubMed Health⌕ Search

Biomedical subjects

B Chávez de Ramírez

Publications and source records attributed to B Chávez de Ramírez.

4 recordsLinked to original sources
PubMed1985

Tight junction formation in cultured epithelial cells (MDCK).

Synthesis and assembly of tight junctions are studied in monolayers of MDCK cells plated at a density sufficient for confluence, allowed to attach for 1 hr, and transferred to fresh media without cells containing or not Ca2+. 20 hr later, while monolayers with Ca2+ have fully developed junctions that confer an electrical resistance across of 346 +/- 51 omega cm2, those without Ca2+ have a negligible resistance. If at this time Ca2+ is added, junctions assemble and seal with a fast kinetics, that can be followed through the development of electrical resistance, penetration of ruthenium red, and electron microscopy. Drugs that impair synthesis, maturation and transport of proteins (cycloheximide, tunicamycin, monensin) indicate that protein components are synthesized early upon plating, do not seem to require N-glycosylation, and are stored in the Golgi compartment. Upon addition of Ca2+ they are transferred to the membrane with the participation of microfilaments but not of microtubules. These components seem to insert directly in the position they occupy in the strands, and the cell circles its perimeter with one strand as early as 15 min, even if in some segments it only consists of a row of particles. New strands develop in association with previous ones, and the pattern completes in 4 to 6 hr. Ca2+ is required for the maintenance of the assembly and also for the sealing with neighboring cells. These processes cannot occur below 25 degrees C. Serum is not required. Polarized distribution of intramembrane particles (IMP) in apical and basolateral regions follows the same time course as junction formation, in spite of the fence constituted by those strands that are already assembled. This suggests that IMP do not redistribute by lateral displacements in the plane of the membrane, but by removal and insertion in the apical and basolateral domains.

Animals↗
PubMed1984

Effect of temperature on the occluding junctions of monolayers of epithelioid cells (MDCK).

In previous works it was demonstrated that the monolayer of MDCK cells behaves as a leaky epithelium where the electrical resistance across reflects the sealing capacity of the occluding junction. In the present work we study whether this sealing capacity can be modified by temperature and whether this is accompanied by changes in the structure of the occluding junction. Monolayers were prepared on disks of nylon cloth coated with collagen and mounted as a flat sheet between two Lucite chambers. The changes in resistance elicited by temperature were large (306% between 3 and 37 degrees C), fast (less than 2 sec), and reversible. An Arrhenius plot of conductance versus the inverse of temperature shows a broken curve (between 22 and 31 degrees C), and the activation energies calculated (3.2 and 4.0 kcal X mol-1) fall within the expected values for processes of simple diffusion. The morphology of the occluding junction was evaluated in freeze-fracture replicas by counting the number of strands and the width of the band occupied by the junction every 133 nm. In spite of the change by 306% of the electrical resistance and the phase transition, we were unable to detect any appreciable modification of the morphology of the occluding junction. Since the freeze-fracture replicas also show a density of intramembrane particles (IMP) different in the apical from that in the basolateral regions of the plasma membrane, as well as differences between face E and face P, we also investigated whether this is modified by temperature. Cold increases the population of IMP, but does not affect their polarization with the incubation time it takes to elicit changes in electrical resistance.

Animals↗
PubMed1982

Occluding junctions of the Necturus gallbladder.

The paracellular conducting pathway of the Necturus gallbladder was studied with electrophysiological and electromicroscopic methods. The first one consists of the passage of short (5 msec) and small (32 microA cm-2) current pulses associated with a voltage scanning of the plane of the epithelium at the apical surface with a microelectrode to detect the regions where current flows. The procedure shows that (a) the conductance is evenly distributed along the intercellular regions along the intercellular spaces of the cells where occluding junctions are located; (b) the field above the occluding junctions has the shape of a bell, so that the junction can be sensed at 1-2 micron from the region where the intercellular space is visualized by light microscopy; (c) the intersections between three cells, in spite of having 3 half-junctions contributing (instead of two), do not have a higher conductance than the rest of the occluding junction. Scanning electron microscopy shows that (a) cells are densely covered by microvilli which interdigitate above the region of the occluding junctions, and (b) are covered by a surface coat. With transmission electron microscopy, (a) the opening of the occluding junctions at the apical border appears irregular, and most of them oblique; (b) in the last microns the actual mouth of the junction may deviate from the course of the interspace. Freeze-fracture replicas indicate that (a) the occluding junction has a uniform width and little variations in the number of strands around the cell, except (b) at intersections between 3 cells where both, its width and the number of strands, increase toward the basal region.

Animals↗