Robertson's comprehensive study of the ultrastructure of cell membranes and membranous cell organelles (Robertson, 1957) demonstrated that many cytoplasmic membranes have basically a similar appearance. The appearance of these membranes when cut in cross-section and seen in the electron microscope is two dark lines about 20 A thick, separated by a less dense space of about 35 A. Conceiving of t...

The views and opinions expressed or implied in this article are those of the author (or authors) and do not necesarily refl ect the position of the National Marine Fisheries Service, NOAA. Abstract—Long-term sustainable management of wild populations should be based on management actions that account for the genetic structure among populations. Knowledge of genetic structure and of the degree o...

The molecular mechanisms by which Ca 2 1 and metal ions interact with the binding sites that modulate the tight junctions (TJs) have not been fully described. Metal ions were used as probes of these sites in the frog urinary bladder. Basolateral Ca 2 1 withdrawal induces the opening of the TJs, a process that is abruptly terminated when Ca 2 1 is readmitted, and is followed by a complete recove...

An Ecopath-Ecosim ecosystem model under development for coastal areas of the Gulf of Mexico simulates responses of 63 biomass pools to changes in fisheries and primary productivity. Ten key species are represented by detailed, multistanza population-dynamics models (31 of the biomass pools) that attempt to account explicitly for possible changes in recruitment rates due to changes in by-catch r...