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Trout are of interest in defining the relationship between fluid and salt balance on cardiovascular function because they thrive in freshwater (FW; volume loading, salt depleting), saltwater (SW; volume depleting, salt loading), and FW while fed a high-salt diet (FW-HS; volume and salt loading). The effects of chronic (>2 wk) adaptation to these three protocols on blood volume ([sup.51]Cr red cell space), extracellular fluid volume ([sup.99m]Tc-diethylene triaminepenta-acetic acid space), arterial (dorsal aortic; PDA) and venous (ductus Cuvier; [P.sub.ven) blood pressure, mean circulatory filling pressure (zero-flow [P.sub.ven]), and vascular capacitance were examined in the present study on unanesthetized rainbow trout. Blood volume, extracellular fluid volume, [P.sub.DA], [P.sub.ven], and mean circulatory filling pressure progressively increased in the order SW < FW < FW-HS. Vascular capacitance in SW fish appeared to be continuous with the capacitance curve of FW fish and reflect a passive volume-dependent unloading of the venous system of FW fish. Vascular capacitance curves for FW-HS fish were displaced upward and parallel to those of FW fish, indicative of an active increase in unstressed blood volume without any change in vascular compliance. These studies are the first in any vertebrate to measure the relationship between fluid compartments and cardiovascular function during independent manipulation of volume and salt balance, and they show that volume, but not salt, balance is the primary determinant of blood pressure in trout. They also present a new paradigm with which to investigate the relative contributions of water and salt balance in cardiovascular homeostasis. fish; unstressed blood volume; mean circulatory filling pressure; osmoregulation; ionoregulation

The glomerular filtration barrier (GFB) is generally considered to consist of three layers: fenestrated glomerular endothelium, glomerular basement membrane, and filtration slits between adjacent podocyte foot processes. Detailed anatomic examination of the GFB has revealed a novel abluminal structure, the subpodocyte space (SPS), identified as the labyrinthine space between the underside of podocyte cell body/primary processes and the foot processes. The SPS covers 50-65% of the filtration surface of the GFB, indicating that SPS may influence glomerular permeability. We have examined the contribution of the SPS to the permeability characteristics of the GFB using multiphoton microscopy techniques in isolated, perfused glomeruli and in the intact kidney in vivo. SPS were identified using this technique, with comparable dimensions to SPS examined with electron microscopy. The passage of the intermediate-weight molecule rhodamine-conjugated 10-kDa dextran, but not the low-weight molecule lucifer yellow ([approximately equal to] 450 Da), accumulated in SPS-covered regions of the GFB, compared with GFB regions not covered by SPS ('naked regions'). Net lucifer yellow flux (taken to indicate fluid flux) through identifiable SPS regions was calculated to be 66-75% of that occurring through naked regions. These observations indicate both ultrafiltration and hydraulic resistance imparted by the SPS, demonstrating the potential physiological contribution of the SPS to glomerular permeability. glomerulus; permeability; podocyte; multiphoton

The cellular distribution of the N[H.sub.2]-terminal electrogenic [Na.sup.+]-HC[O.sup.-.sub.3] cotransporter (NBCel) variants NBCel-A and NBCel-B has been investigated in rat kidney and submandibular gland (SMG) under physiological conditions and after systemic acid-base perturbations. Moreover, the in vivo data were complemented in vitro by using an immortalized cell line derived from the S1 segment of the proximal tubule (PT) of normotensive Wistar-Kyoto rats (WKPT-0293 C1.2). NBCel-A was basolaterally localized in PT ceils, whereas NBCel-B exhibited intracellular and basolateral distribution. SMG showed transcript and protein expression for NBCel-A and NBCel-B. NBCel-B was basolaterally localized in duct cells; NBCel-A was found intracellularly in salivary striated ducts and apically in main duct cells. Acute metabolic acidosis significantly increased cells that showed basolateral NBCel-A in the PT, indicating increased HC[O.sup.-.sub.3] reabsorption, and significantly decreased ceils that exhibited basolateral NBCel-B in the salivary ducts, suggesting decreased HC[O.sup.-.sub.3] secretion. Chronic acidosis had no effect on NBCel distribution in PT but significantly increased the percentage of cells with basolateral NBCel-A in salivary striated duct cells, suggesting increased HC[O.sup.-.sub.3] reabsorption. In contrast, chronic alkalosis caused adaptive redistribution of NBCel-A and NBCel-B in renal PT, favoring decreased HC[O.sup.-.sub.3] reabsorption. In vitro, WKPF-0293 C1.2 ceils expressed key acid-base transporters. Extracellular alkalosis downregulated NBCel-A protein. WKPT-0293 C1.2 cells are therefore a useful model to study renal acid-base regulation in vitro. The results propose redistribution of the transporters as a potential posttranslational regulation modus during acid-base disturbances. Moreover, the data demonstrate that renal PT and salivary duct epithelia respond to acid-base disturbances by an opposite redistribution pattern for NBCel-A and NBCel-B, reflecting specialized functions as the HC[O.sup.-.sub.3]-reabsorbing and HC[O.sup.-.sub.3]-secreting epithelium, respectively. acid-base homeostasis; bicarbonate transport

In the mammalian CNS, hypoxia causes a wide range of physiological effects, and these effects often depend on the stage of development. Among the effects are alterations in pH homeostasis. [Na.sup.+]-coupled HC[O.sup.-.sub.3] transporters can play critical roles in intracellular pH regulation and several, such as NCBE and NBCn1, are expressed abundantly in the central nervous system. In the present study, we examined the effect of chronic continuous hypoxia on the expression of two electroneutral Na-coupled HC[O.sub.3] transporters, SLC4a7 (NBCn1) and SLC4a10 (NCBE), in mouse brain, the first such study on any acid-base transporter. We placed the mice in normobaric chambers and either maintained normoxia (21% inspired [O.sub.2]) or imposed continuous chronic hypoxia (11% [O.sub.2]) for a duration of either 14 days or 28 days, starting from ages of either postnatal age 2 days (P2) or P90. We assessed protein abundance by Western blot analysis, loading equal amounts of total protein for each condition. In most cases, hypoxia reduced NBCn1 levels by 20-50%, and NCBE levels by 15-40% in cerebral cortex, subcortex, cerebellum, and hippocampus, both after 14 and 28 days, and in both pups and adults. We hypothesize that these decreases, which are out of proportion to the expected overall decreases in brain protein levels, may especially be important for reducing energy consumption. electroneutral; bicarbonate transporter; SLC4; central nervous system

Abstract: Brown trout (Salmo trutta) show large phenotypic plasticity. Juveniles may reside in their native freshwater habitat until maturation or migrate into the ocean as 1- to 3-year-old smolts. Sea-going [...]

The osmotic, ionic and haematological responses of the Port Jackson shark and the stingaree Trygonoptera testacea have been studied following exposure to diluted seawater. The increased body weight of the Port Jackson sharks was double that of the stingaree. The haemodilution shown by the Port Jackson sharks lead to a greater reduction in plasma compared to the stingaree. The stingaree's ability to minimize body-weight gain in diluted seawater is probably due to increased net water efflux.

Trehalose, a nonreducing disaccharide, plays an important physiological function in several bacteria and fungi. Some commercial strains of the Saccharomyces cerevisiae yeast have trehalose levels higher than 10% of the cell dry weight. Those strains having high trehalose levels, also exhibit increased dehydration resistance. The roles of trehalose and glycerol in yest cell survival when subjected to osmotic stress have been investigated, and results suggest that intracellular trehalose concentration is related directly to survival.

Ion channels activated by stretch or cell swelling (SAC) are observed in a variety of cells. Investigations have been undertaken to determine whether SACs regulate cell volume in mammalian cardiac myocytes. A swelling-induced, Gdsuper3+-sensitive current i rabbit ventricular myocytes was undertaken, and its role in cell volume regulation studied.

Betaine and inositol decrease the glycerophosphocholine (GPC) content of cultured Madin-Darby canine kidney cells by increasing GPC breakdown by GPC:choline phosphodiesterase. The effect of betaine and inositol is higher in isosmotic or high-NaCl medium than that in high-urea medium. This is due to inhibition of betaine and inositol accumulation by urea. Maintenance of total osmolyte level involves the reciprocal control of GPC, with respect to other related osmolytes, in response to high tonicity.

The regulation of K+ ion, N(super epsilon)-acetyl-beta-lysine, glycine betaine, and alpha-glutamate levels in response to osmotic effects is responsible for the mechanism of halotolerance in Methanosarcina spp. An increase in osmolality from 0.3 to 1.0 osmol/kg increases the K+ ion concentration and the synthesis of alpha-glutamate in M. thermophila. At osmolalities above 1.0 osmol/kg, the alpha-glutamate levels remain steady and the level of beta-amino acid N(super epsilon)-acetyl-beta-lysine increases.

Larval tolerance of Penaeus japonicus to ambient ammonia increases from the nauplius stage to late juvenile. Decreased osmoregulatory capacity in late juveniles depends on ammonia dosage. The time course of exposure indicates the time-dependent effect of ammonia on osmoregulation. Effects of exclusive ambient ammonia on the physiology of shrimps are reversed upon return to control conditions.

Amphipod Gammarus oceanicus exhibits a significantly increased oxygen consumption rate in summer when compared to that during other seasons. Acclimation of amphipods to low temperatures in winter and high temperatures in summer reveals the insensitivity of oxygen consumption rate to temperature. Sea water of low osmolality induces greater expenditure in maintaining osmotic and ionic balance. Changes in seawater osmolality causes a change in the concentration of sodium in the haemolymph.

Cellular growth in culture is influenced by angiotensin (ANG) II. Serum and plasma are necessary to observe mitogenic action, but the existence of angiotensinases cause the degradation of angiotensin peptides, when the concentration of serum is low. ANG-II must be prevented from disintegrating to allow its exclusion, when it stimulates mitogenesis in a serum- or plasma-containing media, where the hyperplastic reaction is absent. The preparation of DNA cannot be sensitively investigated by a serum-free medium.

The physiology and ultrastructure of important and inner medullary collecting duct (IMCD) cells are influenced by arginine varopressin (AVP) stimulation. The connection between ultra-structural modifications in the terminal IMCD (tIMCD) and the calculated alterations in water permeability are examined. Separate perfused rat tIMCD portions are induced with AVP or cyclic monophosphate (cAMP), which cause modifications in the ultrastructure. A calculation of the number of coated pits in the apical membrane and the uptake of luminal markers are examined.

Skate erythrocytes release the beta-amino acids, taurine and beta-alanine, and swell in a hypnotic medium and reduce their volume. A net efflux and an increase in the sodium ion influx is exhibited by these amino acids. Several inhibitors of bond 3-mediated anion transport inhibit the reduction in cell volume and an increase in amino acid transport. The mechanism of volume-activated amino acid transportation is characterized.

Experiments in osmoregulation were conducted on one-day-old brine shrimp, Artemia sp. metanauplii, over a period of six hours at five degree increments in temperature from 15 to 35 degrees centigrade. Alterations of incubation temperature resulted in heightened permeability and drinking rates, which peaked at 35 degrees centigrade. High drinking rates revealed that drinking has other purposes than osmoregulation, and can be connected to respiration and feeding in the early stages of brine shrimp development.