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At least 919 records · Page 51Linked to original sources
PubMed1980

Transport functions of the gallbladder.

The absorptive functions of the gallbladder are responsible for concentrating the Na+ salts of bile acids during interprandial periods. This can be attributed entirely to its ability to absorb NaCl (and NaHCO3) and water in isotonic proportions, thus reducing the volume of hepatic bile by 80%--90%. The results of studies employing gallbladders of several species are consistent with the presence of neutral NaCl (and NaHCO3) absorption that is due to the presence of a coupled (one-for-one) NaCl entry process at the mucosal membrane. Active Na+ extrusion from cell to serosal solution appears to provide the energy for cellular Cl- accumulation, and thus for transepithelial Cl- transport. The mechanism of Cl- exit from the cell to serosal solution is uncertain andrequires further study. Rabbit gallbladder provided an ideal preparation for the characterization of NaCl cotransport and continues to be the tissue of choice for further study of this mechanism. Electrophysiological studies support the concept of nonconductive NaCl cotransport and also suggest that departures from the process of strictly neutral salt absorption may be related to the presence of additional (diffusional) pathways for Na+ and/or Cl- movement across the mucosal membrane so that the mechanistic constraint of neutral copuling between the absorptive movements of these ions is removed. Under these conditions, a significant serosa-positive transepithelial PD is observed and a fraction of Cl- absorption may be electrically coupled to that of Na+. Water is absorbed passively by virtue of osmotic coupling to electrolyte transport. A region of hypertonicity generated within the epithelium, at the level of the lateral intercellular space, provides the driving force for osmotic water flow. In view of the high osmotic water permeability of the gallbladder, the degree of hypertonicity required to account for the rate of water absorption is probably smaller than originally anticipated and is likely to be difficult to detect experimentally. Recent studies of the effects of humoral and pharmacological agents on electrolyte and water transport suggest that the rate of fluid absorption may be subject to physiological regulation. For example, secretin, which stimulates a HCO3--rich biliary secretion, also inhibits the reabsorption of this HCO3--rich fluid by the gallbladder, and in this manner may expedite the neutralization of the duodenal lumen. Inquires aimed at defining the physiological control of the absorptive functions of the gallbladder should provide an exciting avenue for future studies.

Absorption↗
PubMed1993

Interpreting peritoneal membrane osmotic reflection coefficients using a distributed model of peritoneal transport.

The relationship between the osmotic reflection coefficient for the peritoneal membrane and that for peritoneal capillaries was derived theoretically using a distributed model of peritoneal transport. The distributed model predicted that the osmotic reflection coefficient for the peritoneal membrane was equal to that for peritoneal capillaries only when the capillary wall was the dominant diffusive solute transport resistance. Under these conditions, moreover, all peritoneal capillaries equally contributed to transperitoneal ultrafiltration. If, on the other hand, interstitial tissue was the dominant diffusive solute transport resistance, then the osmotic reflection coefficient for the peritoneal membrane was lower than that for peritoneal capillaries and only superficial capillaries participated in transperitoneal ultrafiltration. Previous experiments have demonstrated that the capillary wall is not the dominant diffusive solute transport resistance for small osmotic solutes across the peritoneal membrane; thus osmotic reflection coefficients for the peritoneal membrane are likely several times less than those for peritoneal capillaries.

Biological Transport↗
PubMed1993

[The enhancement by hydrocortisone of the hydro-osmotic effect of vasopressin and cAMP in the frog bladder wall].

Hydroosmotic effect of vasopressin enhanced by the addition of hydrocortisone to serosal Ringer solution of frog urinary bladder. The osmotic permeability of the urinary bladder wall increased after inhibition of cAMP phosphodiesterase by isobutylmethylxanthine followed by the addition of cAMP; hydrocortisone modulated the action of cAMP phosphodiesterase and consequently increased the effect of isobutylmethylxanthine.

Animals↗
PubMed1997

A novel method to determine the diffusional water permeability of oocyte plasma membranes.

Measurements of the cell membrane diffusional water permeability (Pd) are important to characterize water passage across water channels and across the lipid bilayer component of the membrane. Existing methods for those measurements are involved; however, we report here a simple procedure to estimate Pd in Xenopus laevis oocytes and similar large cells. Due to the different densities of H2O and D2O (heavy water), an oocyte transferred from normal medium to a D2O-based medium floats initially, but subsequently sinks when a certain amount of the water originally in them is replaced by the D2O that diffuses in. We describe how the 'flotation time' (time that oocytes float in a heavy water solution before they start sinking) yields the Pd of the plasma membrane. Determination of Pd by this procedure and by the rate of tritiated water (T2O) efflux give for Pd results which are very close: 2.2 +/- 0.2 (n = 8) and 2.0 +/- 0.1 (n = 6) microns/s, respectively (T = 10 degrees C). Furthermore, our method detects the increase in Pd elicited in oocytes by either expression of water channel proteins, or by treating them with the pore-forming antibiotic amphotericin B. This method appears useful to gauge the expression and function of pore-forming, water-permeable membrane proteins.

Amphotericin B↗
PubMed1994

Clinical significance and detection of individual differences and changes in transperitoneal transport.

A review is given on the pathophysiology of the transport of solutes and fluid during continuous ambulatory peritoneal dialysis. Special attention is paid to the assessment of peritoneal permeability in individual patients, its inter- and intraindividual variability, the effect of systemic disease, some regulatory mechanisms, and alterations observed during long-term continuous ambulatory peritoneal dialysis.

Adult↗
PubMed1970

Molecular aspects of polyene- and sterol-dependent pore formation in thin lipid membranes.

Amphotericin B modifies the permeability properties of thin lipid membranes formed from solutions containing sheep red cell phospholipids and cholesterol. At 10(-6)M amphotericin B, the DC membrane resistance fell from approximately 10(8) to approximately 10(2) ohm-cm(2), and the membranes became Cl(-)-, rather than Na(+)-selective; the permeability coefficients for hydrophilic nonelectrolytes increased in inverse relationship to solute size, and the rate of water flow during osmosis increased 30-fold. These changes may be rationalized by assuming that the interaction of amphotericin B with membrane-bound sterol resulted in the formation of aqueous pores. N-acetylamphotericin B and the methyl ester of N-acetylamphotericin B, but not the smaller ring compounds, filipin, rimocidin, and PA-166, produced comparable permeability changes in identical membranes, and amphotericin B and its derivatives produced similar changes in the properties of membranes formed from phospholipid-free sterol solutions. However, amphotericin B did not affect ionic selectivity or water and nonelectrolyte permeability in membranes formed from solutions containing phospholipids and no added cholesterol, or when cholesterol was replaced by either cholesterol palmitate, dihydrotachysterol, epicholesterol, or Delta5-cholesten-3-one. Phospholipid-free sterol membranes exposed to amphotericin B or its derivatives were anion-selective, but the degree of Cl(-) selectivity varied among the compounds, and with the aqueous pH. The data are discussed with regard to, first, the nature of the polyene-sterol interactions which result in pore formation, and second, the functional groups on amphotericin B responsible for membrane anion selectivity.

Alkenes↗
PubMed2007

Cellular properties of human erythrocytes preserved in saline-adenine-glucose-mannitol in the presence of L-carnitine.

L-Carnitine (LC) in the preservation medium during storage of red blood cells (RBC) can improve the mean 24-hr percent recovery in vivo and increase RBC life-span after reinfusion. The purpose of the study was to investigate the differences in the biochemical properties of RBCs stored in the presence or absence of LC, and the cell-age related responses to storage conditions and to LC. RBC concentrates in saline-adenine-glucose-mannitol (SAG-M) were stored in the presence or absence of 5 mM LC at 4 degrees C for up to 8 weeks. RBC subpopulations of different densities were prepared by centrifugation on Stractan density gradient. Cells were sampled at 0, 3, 6, and 8 weeks, and hematological and cellular properties analyzed (MCV, MCHC, 4.1a/4.1b ratio as a cell age parameter, intracellular Na(+) and K(+)). After 6 weeks, MCV of RBC stored in the presence of LC was lower than that of controls (6 weeks MCV: controls 95.4 +/- 1.8 fl; LC 91.5 +/- 2.0 fl; n = 6; P < 0.005). This was due to swelling of control cells, and affected mainly older RBCs. LC appeared to reduce or retard cell swelling. Among the osmotically active substances whose changes during storage could contribute to cell swelling, only intracellular Na(+) and K(+) differed between stored control RBCs and LC-treated cells. LC reduces the swelling of older cells during storage at 4 degrees C in SAG-M, possibly by acting on the permeability of cell membrane to monovalent cations.

Adenine↗
PubMed1997

Characterization of a swelling-activated anion conductance in homozygous typing cell hepatoma cells.

Liver cell volume and intracellular ion concentrations are maintained within a narrow physiologic range by regulated changes in membrane ion permeability. These studies of homozygous HTC hepatoma cells, a model liver cell line, evaluate the relationship between cell volume and membrane ion permeability, and assess the possibility that cell swelling allows the efflux of the intracellular osmolite taurine through the opening of a conductive pathway. Cell swelling induced by exposure to hypotonic solutions (203 mOsm) caused a rapid increase in cell volume, followed by recovery toward basal values. Volume recovery was inhibited by Cl- depletion or by exposure to the putative Cl- channel blocker 5-nitro-2-(3-phenylpropyl-amino) benzoic acid (NPPB) (25 micromol/L). Swelling increased the efflux rates of 36Cl (181% +/- 15%, P < .01) and 125I (310% +/- 21%, P < .01). In whole cell patch clamp recordings, cell swelling induced by 1) exposure to hypotonic solution or 2) intracellular perfusion with hypertonic sucrose-containing solutions activated an anion-selective current which was outwardly rectified and showed time-dependent inactivation at depolarizing potentials. The current density at -80 mV increased proportionally with increases in the transmembrane osmotic gradient from basal values of -1 pA/pF to maximal values of 70 pA/pF with 100 mmol/L sucrose in the pipette. Basal taurine permeability was low, but cell swelling increased the efflux of [1,2-3H]taurine to 1,587% +/- 172% of basal levels (P < .05). Intracellular perfusion with hypertonic solutions activated currents carried by anionic taurine, with an estimated taurine/Cl- permeability ratio of .88 +/- .17 for whole cell currents. These studies demonstrate that the HTC membrane anion permeability is closely coupled to changes in cell volume, and that the recovery from swelling depends upon activation of anion-selective conductance pathways permeable to both Cl- and taurine.

Animals↗