Regulation of brain water permeability by centrally-released vasopressin.

A number of ultrastructural and cytochemical techniques were used to study intact epithelial cells lining the frog urinary bladder: high resolution autoradiography after administration of [3H]glucosamine or [3H]fucose; 125I iodination of external protein; concanavalin A-peroxidase, periodic acid-chromic acid silver methenamine; and colloidal thorium. Results indicate that the material (probably glycoprotein) coating the apical surface differs from that which lines the lateral and basal surfaces. After dissociation and isolation of the epithelial cells, the material previously confined to the apical surface invaded progressively the opened "tight junctions" (about 5 min), then the lateral membranes (about 40 min), and finally the basal membrane (about 80 min): at that time, the whole cell surface was entirely enveloped by the apical material. Since, on the one hand, the reacting material was confined to the apical surface when the tight junctions were closed (in intact epithelial cells) and since, on the other hand, the apical material was sliding down the laterobasal membranes when the tight junctions were opened (in dissociated cells), it may be concluded that tight junctions contribute to maintain the cell surface specialization in epithelia.

https://rupress.org/jcb/article-pdf/71/3/907/1072205/907.pdf

Redistribution of surface macromolecules in dissociated epithelial cells.

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu interieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis. The focus is on recent studies of adaptations and newly discovered mechanisms of acclimatization during transitions of animals between different osmotic environments. Special attention is paid to hypotheses about the diversity of cellular organization of osmoregulatory and excretory organs such as glomerular kidneys, antennal glands, Malpighian tubules and insect gut, gills, integument and intestine, with accounts on experimental approaches and methods applied in the studies. It is demonstrated how knowledge in these areas of comparative physiology has expanded considerably during the last two decades, bridging seminal classical works with studies based on new approaches at all levels of anatomical and functional organization. A number of as yet partially unanswered questions are emphasized, some of which are about how water and solute exchange mechanisms at lower levels are integrated for regulating whole body extracellular water volume and ion homeostasis of animals in their natural habitats. © 2014 American Physiological Society.

Osmoregulation and excretion

Isolated renal cortical collecting tubules obtained from rabbits treated chronically with desoxycorticosterone acetate (DOCA) have been found to possess elevated transepithelial potential differences and a greatly increased capacity for ion transport. Structural exmination of tubules from rabbits exposed to either DOCA or dexamethasone for 11--18 d reveals a marked increase in basolateral cell membrane area in these tubules. Morphometric analysis shows that this effect is specifically on the basolateral membrane area of only one of the two cell types found in this nephron segment. Increases of greater than 140% and 90% are found for the basolateral membrane area of the principal cells for DOCA and dexamethasone, respectively, but no change could be detected in the basolateral membrane area of the intercalated cells found in this nephron segment. No siginificant changes were found in luminal membrane area, cell number, or cell volume for either cell type. These observations demonstrate that significant changes in membrane area can occur in differentiated epithelia and suggest that this may be an important mechanism for modulating epithelial transport capacity.

https://rupress.org/jcb/article-pdf/81/2/439/1073646/439.pdf

Modulation of cell membrane area in renal collecting tubules by corticosteroid hormones

The systemic actions of aldosterone are well documented; however, in comparison, our understanding of the cellular and molecular mechanisms by which aldosterone orchestrates these actions is rudime...

https://www.physiology.org/doi/pdf/10.1152/ajprenal.00320.2001

New ideas about aldosterone signaling in epithelia.

The mucosal epithelium of the toad urinary bladder reabsorbs sodium, acidifies the urine, and is responsive to neurohypophyseal hormnones. Mucosal epithelial cells, consisting of two major morphologic cell types, "mitochondria-rich" and "granular," were removed from the bladder and separated by density gradient centrifugation. The mitochondria-rich cells contained three times as much carbonic anhydrase activity as the granular cells. Oxytocin caused a 235 percent increase in the adenosine 3',5'-monophosphate content of mitochondria-rich cells but had no effect on the granular cells. The evidence indicates that the mitochondria-rich cell, which accounts for only 15 percent of the mucosal cells, plays a major role in the mediation of sodium ion and hydrogen ion transport in the toad bladder and is a specific site of action of neurohypophyseal hormones.

https://science.sciencemag.org/content/sci/184/4138/797.full.pdf

Partition of Tissue Functions in Epithelia: Localization of Enzymes in "Mitochondria-Rich" Cells of Toad Urinary Bladder

Aldosterone (the 8,11-hemiacetal 0f 11beta,21-dihydroxy-3,20-dioxo-4-pregnen-18-al) markedly stimulates sodium transport in a number of epithelial tissues. We have attempted to determine whether aldosterone induces the synthesis of specific protein(s) in the course of its action upon the toad urinary bladder. Paired hemibladders were incubated in media containing either [3H]methionine or [35S]methionine; aldosterone in physiologic concentrations was added to one bath and, after incubation, the intact "mitochondria-rich" (MR) and "granular" (G) mucosal cells were isolated. The ratio (3H/35S) was used to identify proteins whose synthesis was induced in the mucosal cells of the steroid-treated bladders. Using exclusion gel chromatography and isoelectric focusing, we identified several aldosterone-induced proteins in the supernatant (105,000 x g) fraction of the MR cell. None was evident in this fraction of the G cell. These proteins have apparent molecular weights ranging from 17,000 to 38,000 and the isoelectric point of the major component is 4.5. Corticosterone (11beta,21-dihydroxy-4-pregnene-3,20-dione) induced the synthesis of proteins in the G cells, but none of these proteins was similar in molecular weight to the aldosterone-induced proteins in the MR cell. Our findings support the hypothesis that aldosterone induces the synthesis of specific proteins and indicate that, in this tissue, these proteins are synthesized by the MR cell.

https://www.pnas.org/content/pnas/72/10/4056.full.pdf

Identification of aldosterone-induced proteins in the toad's urinary bladder.

The effects of oxytocin upon tissue cAMP content and short-circuit current (SCC) were measured in the urinary bladder of the toad, Bufo marinus Tissue cAMP levels doubled before any increment in SCC was observed, the two hormone responses were quantitatively related, and a threshold level for an effect of cAMP upon sodium transport was demonstrated The period of time over which cAMP levels continued to rise after the threshold level had been attained seemed invariant with hormone concentration The rate at which cAMP levels rose increased with hormone concentration yielding hormone concentration-dependent maximal levels The decay of cAMP levels was delayed when sodium influx was curtailed, suggesting a sodium-regulatory effect upon tissue cAMP levels

/pdf/cyclic-amp-and-sodium-transport-quantitative-and-temporal-9s0q0qzu9a.pdf

Victor S. Sapirstein

Papers

Partition of Tissue Functions in Epithelia: Localization of Enzymes in "Mitochondria-Rich" Cells of Toad Urinary Bladder

Identification of aldosterone-induced proteins in the toad's urinary bladder.

Cyclic AMP and sodium transport. Quantitative and temporal relationships in toad urinary bladder.