Transmural Transport Research Articles

In vitro and in situ absorption of methionine sulfoxide in rat small intestine.

Absorption of methionine and its sulfoxide was investigated in vitro with everted sacs and in situ with circulated loops of rat small intestine. Transmural transport and tissue accumulation of methionine sulfoxide in the everted sacs were in fair agreement with those of methionine. Apparent kinetic parameters for the difference of transmural transport in the absence and presence of 10−5 m carbonylcyanide m-chlorophenylhydrazone, i.e. for the energy-dependent active transport, were similar for both methionine and its sulfoxide. Methionine was found at a low level in the serosal fluid of the everted sac on incubation with methionine sulfoxide. It was attributed to the methionine leaked out from the tissue but not to that formed by reduction of methionine sulfoxide during the course of intestinal transport. Similar transport was also observed in situ in circulated intestinal loops for methionine and its sulfoxide. The absorption efficiency of methionine sulfoxide in the small intestine is not the reason for ...

Ribonucleic acid changes in medial cells in evans blue positive regions of the dog aorta

Evidence is presented supporting the feasibility of using cytophotometric analysis of cellular azure B-RNA dye binding as a cytochemical marker of metabolic alterations in medial smooth muscle cells underlying aortic areas having spontaneously occurring increased uptake of Evans blue dye. Focal areas of enhanced permeability or intra-aortic macromolecular accumulation (demarcated by in vivo uptake of Evans blue dye) exhibited 20–40% higher extents of azure B staining in intimal, medial, and adventitial compartments when compared to corresponding compartments in dye-impermeable regions. No discernible differences were evidenced in deoxyribonucleic acid levels (using Feulgen-DNA cytophotometry) or in the histological appearance (using conventional staining) between Evans blue-positive and negative aortic specimens. The overall data suggest that (1) focal differences in cellular azurophilia are attributable to differences in rates of uptake or accumulation of plasma constituents in Evans blue-permeable and impermeable aortic regions, and (2) the permeability-associated increase in azurophilia is due to an increase in ribosomes and reflects a compensatory activation of metabolic processes in response to an increased uptake and transmural transport of plasma macromolecules.

Effect of arterial stretch on transmural albumin and Evan's blue dye transport.

The influence of arterial wall circumferential stretch (lambda) on the 32-min diffusive mural uptake of 125I-albumin and of Evan's blue dye (EBD) across the injured endothelial surface was studied in the intimal-medial preparation of the canine descending thoracic aorta (DTA). Albumin uptake (MA nmol/cm2) was measured by standard gamma counting techniques and the corresponding EBD uptake (ME) by the reflectance method. MA and ME were measured at a physiological stretch (lambda = 1.4) and at a hypertensive stretch (lambda = 1.8) at four equispaced locations (z) along the DTA. When lambda was changed from 1.4 to 1.8, the average percentage change of MA was -2% and of ME was -4%. These decreases were not significant (P greater than 0.10), and we conclude that arterial wall stretch exerts only minor influence on the parameters governing albumin and EBD-albumin accumulation in the intimal surface of the deendothelialized arterial intimal-medial tissue system.

Inhibitory action of DIDS on chloride transport across the amphibian cornea.

1. DIDS (4,4'-diisothiocyano-2,2'-stilbene disulphonic acid) reduced the CI Isc across the toad's (Bufo marinus) cornea. It acted on either the aqueous or tear side and these effects were additive. 2. The reduction in the Isc was equivalent to the decline in the undirectional flux of Cl from the aqueous to the tear side. The Cl flux from tear to aqueous was not changed. 3. DIDS did not change transmural Na transport. 4. The action of the diuretic bumetanide, which also inhibits Cl transport was additive to that of DIDS when both compounds were present on the aqueous though not when they were on the tear side of the cornea. 5. The results are consistent with the role of a Cl-/anion exchange mechanism in active Cl transport across the cornea. 6. A hypothesis regarding the interactions and site of action of bumetanide in relation to that of DIDS, and the Cl transport process, is proposed.

Superficial or Membrane Digestion of Peptides in Dinitrophenol-Inhibited Rat Small Intestine

1. Hydrolysis of peptides has been measured in isolated rat small intestine perfused with a pancreatic digest of lactalbumin in the presence of 2,4-dinitrophenol. 2. Although transport of water and amino acids was severely inhibited by 2,4-dinitrophenol, peptide hydrolysis to free amino acids was apparently unimpaired. 3. Only a small fraction of the hydrolysis observed could be accounted for by leakage of enzymes into the lumen. 4. The results show that the brush-border enzymes proximal to the transport mechanism(s) can be an important site of hydrolysis of peptides to amino acids under conditions where the transport of unhydrolysed peptides is inhibited. The results are consistent with the concept of membrane (contact) digestion, although the significance of intracellular hydrolysis and of transmural transport of intact peptides is also discussed.

Sodium uptake across the apical border of the isolated turtle colon: confirmation of the two-barrier model.

The initial rate of Na uptake by the turtle colon from the mucosal bathing solution consists of two operationally distinct components. One component is a linear function of mucosal Na concentration, is unaffected by amiloride, and appears to represent Na uptake into the paracellular shunt path. The major component of Na uptake is abolished by amiloride and is virtually equal to the short-circuit current over a wide range of mucosal Na concentrations, suggesting that this portion of Na uptake represents Na movement into Na-transporting cells of the colon. The amiloride-sensitive component of Na uptake, at low mucosal Na concentrations, was unaffected if net Na transport was abolished by ouabain. Similarly, at low mucosal Na concentrations the amiloride-sensitive conductance of the colon was identical in the presence and in the absence of net Na transport. These results show that the isolated turtle colon behaves as two distinct barriers to transmural Na transport, an apical barrier blocked by amiloride and a more basal-lying barrier where active, transmural Na transport is blocked by ouabain. In addition, these experiments appear to provide the first unambiguous demonstration that the initial-rate isotope uptake technique can provide a direct measure of the properties of the amiloride-sensitive barrier to transmural Na movement, presumably the apical membranes of the Na-transporting cells. The results are consistent with the notion that the rate of transmural active Na transport and the conductance of the active Na-transport path are determined by the properties of the apical membrane.

Folic acid transport by mammalian small intestine.

The unidirectional influx of folic acid across the mucosal border of hamster duodenum and rat jejunum was determined. Influx follows saturation kinetics, is sodium-dependent, and is inhibited by methotrexate and is sodium-dependent, and is inhbited by methotrexate and folinic acid in the mucosal bathing solution. In hamster duodenum, the maximal influx is 1.2 nmol/(cm2.h), and the folic acid concentration required to give a half maximal influx (Km) is 7.2 micron.. At mucosal folic acid concentration of 1.5 micron, influx is reduced at least 65% by removal of sodium from the bathing solution. The influx process is significantly inhibited by cyanide and 2,4-dinitrophenol. The possibility was evaluated that the acidic microclimate at the brush border regulates the rate of folic acid transport and that inhibition of transmural transport by sodium-free media, ouabain, and methotrexate is brought about indirectly by an increase in pH of the microclimate. The data favor the alternative concept of a sodium-dependent carrier mechanism for entry of folic acid into the cells. The information presented is consistent with active transport of folic acid by a sodium-gradient mechanism, but additional information will be necessary to substantiate such a model.

Examination of transport equations pertaining to permeable elastic tubules such as Henle's loop

The transport equations applicable to loops of Henle and similar elastic permeable tubules were re-examined to assess the effect of radial transport resistance in the lumen and tubule geometry on solute transport. Active transport at the wall as well as external gradients equivalent to a 2--1,000-fold concentration increase per centimeter of distance were considered. Wall permeabilities and active transport constants were varied up to 2 . 10(-2) cm/s. It is shown that for conditions applicable to the loop of Henle, resistance to radial solute transfer in the lumen is negligible, both for passive and active transmural transport with concomitant water flux, and that axial dispersion further reduces that resistance. These conclusions apply equally to conical and elliptical geometries likely to arise in loop operation. The validity of Poiseuille's equation for these geometries is discussed. Ii is concluded that the one-dimensional transport equations are a valid representation of loop operation.

A mathematical model of transmural transport of oxygen to the retina.

A mathematical model of transmural transport of oxygen to a metabolizing retina is presented based on the equations of fluid dynamics. The equations of oxygen transfer are derived and then solved subject to the condition that the capillaries begin to transport oxygen at an initial time. The resulting transient analysis gives us insight into how diffusive and filtrative processes lead to the oxygen distributions both inside and outside capillaries. On the other hand, the steady state solution allows us to predict the cutoff intraocular pressure above which no oxygen is transferred to retinal tissue. It also gives quantitative relationships which allow us to postulate how intracapillary hypertension counterbalances elevated intraocular pressures and how low pressure glaucoma may arise from ineffective diffusive and filtrative processes of oxygen transport.

Transport characteristics of isolated newborn rabbit ileum.

Segments of ileum from newborn rabbits were mounted as flat sheets in Lucite chambers and transmural fluxes of Na, Cl, and alanine were measured in the absence of electrochemical potential gradients. In the presence of 140 mM Na, the ileum of the newborn exhibited a serosa-positive electrical PD and a corresponding short-circuit current (Isc) which was markedly enhanced by the addition of D-glucose of L-alanine to the mucosal solution. Alanine-induced increments in Isc were a saturable function of the mucosal alanine concentration. In the presence of Na, alanine was actively absorbed, and the net alanine flux was a saturable function of alanine concentration. When the Na in the bathing solutions was completely replaced by choline, Isc declined to near zero, and the response of Isc to mucosal alanine was abolished. In addition, active amino acid transport was abolished in the absence of Na. In the absence of alanine, the isolated ileum of the newborn actively absorbed Na and Cl, and the algebraic sum of the net movements of these ions accounted for Isc. In the presence of alanine, active Cl transport was abolished and Isc was equal to the net Na absorption. These results indicate that the ileum of the newborn rabbit is similar to that of the adult in its ability to actively absorb Na, Cl, and alanine, but differs from the ileum of the adult by having a greater passive permeability to ions and amino acid, and differs particularly with regard to the effect of mucosal alanine on transmural ion transport.

A mathematical model of transmural transport of oxygen to the retina

A mathematical model of transmural transport of oxygen to the retina

Effect of semistarvation on kinetic parameters for the in vitro accumulation and transport of L-leucine in rat small intestine.

The effects of semistarvation on the kinetics of the tissue accumulation and the transmural transport of l-leucine were assessed in vitro in the rat jejunum. The Kt calculated for the tissue accumulation was slightly reduced, but the value for transmural transport differed insignificantly after semistarvation. The Vmax’s were unanimously enhanced in semistarvation for both the accumulation and the transport, regardless of the basis of expression. Semistarvation caused a profound increase in the diffusive component of the transport when assessed using carbonyl cyanide m-chlorophenylhydrazone. Energy-dependent, active component of the transport was however even significantly greater in semistarved intestine than in fed control. These results are compatible with the notion that semistarvation improves intestinal transport capacity through increase in the Vmax, which probably correlates with ‘carrier’ population, and concomitantly in the diffusive permeability across brush border and/or intestinal wall.

Solute composition of the osmotic space of ureteral urine in dehydrated chickens ( Gallus domesticus)

1. 1. The concentrations in ureteral urine of Na, Cl, K, NH 4, total CO 2, urea, Ca, Mg, phosphate, and pH and osmolality were measured in dehydrated chickens receiving either wheat and barley or commerical chicken food, which has NaCl added. 2. 2. Control by measurement of vapour pressure and relative humidity show that osmolality determined as freezing-point adequately expressed the chemical potential of water of the urine. 3. 3. The solutes accounted for 74% of the osmolality on commercial food. In the seed-eating birds K-NH 4-phosphate may constitute more than half of the total urine osmolality. As the urine is stored in the cloaca the transmural transport of, and permeability to, these ions should be measured.

Colonic absorption of bacterially synthesized vitamin K2 in the rat.

Colonic absorption of bacterially synthesized vitamin K2 ([3H]menaquinone-9) was studied with everted rat colonic sacs in vitro. The mean +/- SE rate of absorption of the vitamin by the colon was 20 +/- 1.45 pmol/min per 100 mg tissue at 300 nM mucosal concentration of the vitamin. The rate of absorption did not change (P greater than 0.10) with the addition of 2,4-dinitrophenol, Na azide, or KCN to the mucosal incubation medium. No evidence for transmural transport of the vitamin was detectable. When the concentration of the vitamin was increased in a stepwise fashion up to 900 nM, the absorption rate remained linear with respect to the mucosal fluid concentration (r = 0.98). Autoradiography indicated that the vitamin accumulated in the mucosal and submucosal layers of the large bowel. Absorption of the vitamin by the large bowel takes place via a passive, nonsaturable process that shows no evidence of energy dependence or carrier mediation. It was concluded that vitamin K2 (bacterial origin) is absorbable by the rat colon in amounts sufficient to meet the daily requirement of the animal and may explain the lack of bleeding problems in the face of episodic lack of dietary vitamin K.

OSMOTIC INHIBITION OF THE NATRIFERIC RESPONSE OF THE TOAD URINARY BLADDER TO VASOPRESSIN

The electrical potential difference and short-circuit current (scc, reflecting active transmural sodium transport) across the toad urinary bladder in vitro was unaffected by the presence of hypo-osmotic solutions bathing the mucosal (urinary) surface, providing that the transmural flow of water was small. Vasopressin increased the scc across the toad bladder (the natriferic response), but this stimulation was considerably reduced in the presence of a hypo-osmotic solution on the mucosal side, conditions under which water transfer across the membrane was also increased. This inhibition of the natriferic response did not depend on the direction of the water movement, for if the osmotic gradient was the opposite way to that which normally occurs, the response to vasopressin was still reduced. The natriferic response to cyclic AMP was also inhibited in the presence of an osmotic gradient. Aldosterone increased the scc and Na+ transport across the toad bladder but this response was not changed when an osmotic gradient was present. The physiological implications of these observations and the possible mechanisms involved are discussed.

Ultrastructural study of erythrophagocytosis in the rat bone marrow. I. Red cell engulfment by reticulum cells.

Previous light microscopic studies have revealed the erythroclastic potential of the rat bone marrow reticulum cells, and call for ultrastructural study of the finer details of this process. Electron microscopy of rat bone marrow which had been stimulated to increase its erythrophagic activity, either by splenectomy or by transfusion of heat denatured erythrocytes, confirmed the central reticulum cell of erythroblastic islands as the main phagocytic cell in bone marrow erythroclasia. The early digestive vacuoles, which are formed by the fusion of erythrophagic vacuoles with lysosomes, correspond to the acidophilic, globular structures which characterize erythrophagocytosis as observed by light microscopy. By forming intrasinusoidal protrusions, the bone marrow reticulum cells engulf circulating effete red cells. The engulfed red cells are then transported intracellularly across the sinusoidal wall for final disintegration in the intraparenchymal part of the reticulum cell. This transmural mode of erythrophagocytosis by reticulum cells most probably demonstrates the fundamental phagocytic mechanism of the bone marrow part of the reticulo-endothelial system. Transmural transport of reticulocytes adherent to reticulum cells during the formation of protrusions illustrates a possible mechanism for liberation of red cells from the bone marrow.

The electrical P.D. across the integument of some neotenous urodele amphibians

1. 1. An electrical P.D. (inside positive) was recorded in vivo across the integument of the neotenous urodeles Amphiuma means, Siren lacertina and Necturus maculosus and this was related to the sodium concentration in the external bathing media. 2. 2. Like in the frog, Rana pipiens, this P.D. in vivo was inhibited when amiloride was placed in the external solutions bathing Amphiuma and Siren but not Necturus. 3. 3. A P.D. and short-circuit current (SCC) was also observed across the skin of Amphiuma and Siren (but not Necturus) in vitro and this was also inhibited by amiloride. In contrast to the responses of the skin of fully metamorphosed amphibians vasotocin did not stimulate the SCC in these neotenous species. 4. 4. Substitution of sulfate for chloride in the external solution in vitro markedly increased the P.D. of frog skin but had no effect on that of Amphiuma or Siren. 5. 5. The results suggest that the exchanges of ions across frog skin are much greater than in the skin of Amphiuma or Siren. A mechanism for active transmural transport of sodium would appear to exist in the skin of these urodeles but the evidence for this in Necturus was equivocal.

Carbohydrate metabolism, placental lactogen and the control of the initiation of lactation.

intact lactose in the everted sac preparation of the rat jejunum. The results were as follows. (1) Approx. 1 % of lactose was absorbed as the intact disaccharide when various concentrations (5-22Om) of lactose were presented to the mucosa. (2) There was a direct linear relationship between lactose concentration and transport rates up to 1 5 0 m lactose. (3) At 2 2 0 m the rate of lactose transport was greater than predicted from the lower concentrations. (4) Neither ouabain nor phlorrhizin inhibited lactose transport. ( 5 ) The ratio between serosal and mucosal concentrations of lactose never exceeded unity. These results indicate that transmural transport of intact lactose occurs by a process of simple passive diffusion. The higher-than-predicted transport rates observed at high concentrations of lactose may be due to substrate saturation of brush-border lactase leading to a build-up of concentration in the microvillus region.

The permeability to carbon of the sinusoidal lining cells of the embryonic rat liver and rat bone marrow.

AbstractThis study is concerned with the passage of carbon particles through the sinusoidal lining cells of bone marrow and embryonic liver of the rat. A carbon suspension (Pelikan C11/1431A, Günther Wagner, Hanover) diluted 1:1 with double strength Tyrode solution, was administered through the aorta for the bone marrow studies and through the umbilical vein for observations on the embryonic liver. The carbon particles have a diameter ranging from 220 to 380 Å with a mean diameter of 280 Å. Within three minutes after the injection, the particulate was present in the extravascular spaces. Neither the sinusoidal walls of the bone marrow nor of the embryonic rat liver prior to 16 days gestation have preformed apertures. In both cases, the carbon particles enter the extravascular space through fenestrae with diaphragms. No carbon particles occur in the junctional spaces between the lining cells. The temporary pores caused by diapedetic blood cells maintain a tight seal and no particulate was observed leaving the vascular space at these sites. At 17 days of gestation, open gaps develop in the endothelial lining of the embryonic rat liver and particulate material leaves the vascular lumen through these openings. The presence of bristle‐coated vesicles containing particulate material at the abluminal side of the lining cells is interpreted as a retrograde uptake by these phagocytic cells rather than as evidence for vesicular transmural transport.

Sodium-dependent sugar transport in the intestine

The transport of sugars across the small intestine and across the brush border membrane of the intestinal epithelial cells is dependent on the presence of sodium in the mucosal bathing medium. In the absence of sodium, cellular accumulation, net transmural transport, and unidirectional influx are all inhibited. Furthermore, sodium influx across the brush border is stimulated by the influx of sugar and the increase in sodium influx is coupled to sugar influx in a ratio of 1:1. A model for sugar transport across the brush border has been proposed in which sugar binds to a membrane site, but only in the presence of sodium is the sugar translocated into the epithelial cell. The driving force for sugar transport is postulated to be the electrochemical gradient for sodium and/or other ions across the brush border membrane and not direct input of metabolic energy. Therefore, sodium-dependent sugar transport in the intestine can be considered an example of co-transport.