Alanine influx across serosal border of Testudo graeca intestine

The influx of alanine across the serosal membrane of Testudo graeca intestinal cells with preserved epithelial orientation was examined. Our results suggest that: 1. The mechanism of alanine influx across the serosal membrane of turtle intesintal cells is a carrier-mediated process that has the characteristics of facilitated diffusion. 2. Alanine influx mechanism is independent of intra- and extra-cellular changes in Na+ and K+ concentrations, and is not altered by reversal of Na+ and K+ gradients across the serosal membrane. 3. In Na+-free media the mechanism of transport of alanine at the mucosal membrane has the same pattern of competitive inhibition by amino acids as the serosal.

Mechanism of inhibition of alanine absorption by Na ricinoleate

The mechanism of inhibition of alanine absorption by Na ricinoleate has been examined in the rabbit intestine. This fatty acid in a concentration of 2--5 mM inhibits alanine absorption in vivo and in vitro. The inhibition is more evident in the jejunum than in the ileum. Strips of ileal mucosa treated with Na ricinoleate gain Na. Sodium ricinoleate inhibits alanine influx across rabbit ileum, even in the presence of a sodium gradient across these cells. The results suggest that the main action of Na ricinoleate is on the alanine-transport system at the brush-border membrane. The fatty acid may also inhibit amino acid absorption by increasing intestinal cell Na concentration, which results in a decreased Na gradient across the brush-border membrane.

Alanine transport across in vitro rabbit vagina

Transmural flux of alanine across the vaginal epithelium of the rabbit is a specialized mechanism. There is a net serosal to mucosal translocation of the amino acid in the absence of a concentration gradient. Changes in reproductive cycle do not influence this mechanism but, in castrated animals, it is abolished. Transport properties of vaginal epithelium is important because of increasing utilization of intravaginal contraceptives.

Regional differences in potassium content of smooth muscle from opossum esophagus

Strips from the proximal part of the smooth muscle segment of opossum esophagus have a significantly higher potassium content (50 +/- 3 meq/kg) than those from the distal part (38 +/- 3 meq/kg). There are no significant differences between the two regions in content of sodium (65 +/- 4 meq/kg in proximal, 71 +/- 3 meq/kg in distal) or chloride (48 +/- 10 meq/kg in proximal, 42 +/- 5 meq/ kg in distal). The mean [14C]inulin uptake is 240 +/- 10 ml/kg in both proximal and distal strips. [14C]polyethylene glycol uptake is smaller and [14C]sucrose and [14C]mannitol uptake in both areas are larger than that of inulin. Intracellular potassium concentration (based on the inulin uptake as an estimate of the extracellular space volume) is significantly higher proximally (71 +/- 3 mM) than distally (52 +/- mM). Ouabain, 10(-4) M, increases the intracellular concentration of sodium and decreases the intracellular concentration of potassium in both the proximal and distal segment. The efflux of 86Rb, measured by a washout technique, is higher in the distal than in the proximal smooth muscle segment. A difference in membrane permeability to rubidium and hence, potassium between proximal and distal smooth muscle segments may account in part for the different intracellular potassium concentrations.

Calcium-prostaglandin aggregation and its effect on prostaglandin uptake by isolated rabbit intestine

A quantitative estimate of the role of calcium ions on the lipid--water partition coefficients of prostaglandin E1 and dinoprost suggested the possibility of prostaglandin molecules and calcium ions aggregating in a 14:1 ratio to produce a lipid-soluble aggregate. The aggregation is postulated to be a characteristic of prostaglandin molecules as compared to simple fatty acids, e.g., 1-octanoic acid, which, in the presence of calcium, behave differently than the prostaglandins. The uptake of prostaglandins by the mucosal surface of the rabbit intestine increased in the presence of calcium. For example, at 25 mM calcium, prostaglandin E1 was transported at approximately twice the rate as in the system containing no calcium. The uptake rate of dinoprost was estimated to be three times faster with 10 mM calcium than in the absence of calcium. Therefore, it is proposed that a carrier-mediated diffusion process, for both the prostaglandin molecules and calciumi ions, takes place in the uptake mechanism. Diffusion coefficients ranging from 0.48 X 10(-5) to 7.19 X 10(-5) cm2/sec and permeability coefficients ranging from 1.04 X 10(-2) to 15.6 X 10(-2) cm/sec were estimated for all systems studied.

Effect on Mn2+ on permeability properties of frog skin

Mn2+ added to the inner bathing solution of frog skin caused a transient increase in potential difference (PD) and a decrease in total skin conductance and mannitol influx. Net Na flux and short-circuit current (Is. c.) were also reduced, the isotopic net flux being reduced more than Is. c. This observed discrepancy appears to be the result of Cl- retention in the outer medium since it was not observed when the skin was bathed in a sulfate-substituted chloride-free solution. The effect of Mn2+ on the inner side of the frog skin appears to be due to a reduced permeation of Na+ and Cl- through the outer barrier of the skin. Addition of Mn2+ to the outer solution bathing the frog skin caused an increase in PD and a smaller increase in Is. c. These changes were not associated with alterations in the fluxes of Na+ or mannitol and were observed only when chloride was present in the bathing solutions. The effect of Mn2+ on this side of the frog skin may therefore be due to a net retention of Cl- in the outer solution.

Effect of bile salts on amino acid transport by rabbit intestine

The effect of bile salts on alanine absorption across four regional sites of rabbit intestine was examined using an in vivo single-pass perfusion technique. Na-deoxycholate at a concentration of 3 mM reduced alanine absorption across all levels of the intestine, and a higher concentration (10 mM) of Na-taurodeoxycholate (TDC) caused only a minimal reduction of alanine absorption in the jejunum. TDC, however, was more effective in in vitro experiments, causing an incrase in transmural serosal-to-mucosal flux of alanine and phenylalanine, particularly when present in both the mucosal and serosal media. It also reduced the mucosal-to-serosal alanine flux rate when present only in the mucosal medium. The influx of these amino acids across the mucosal brush border membrane was also decreased by TDC. These amino acid transport changes correlated fairly well with some observed histological changes of the intestinal epithelium. This suggests that bile salt inhibition of amino acid absorption is nonspecific in type and can be mainly explained as being the result of an injurious action of these surface-active agents on the rabbit intestine.

Alanine efflux across the serosal border of turtle intestine

The exit of alanine across the serosal border of the epithelial cells of turtle intestine was measured by direct and indirect techniques. A decrease or an increase in cell Na did not affect the amino acid flux from cell to serosal solution. Cells loaded with Na and alanine did not exhibit any extrusion of alanine when their serosal membranes were exposed to an Na-free medium containing alanine. However, substantial amino acid extrusion was observed across the mucosal cell border under similar conditions. Although alanine flux across the serosal membrane appeared to be Na-independent, it showed a tendency toward saturation as cellular alanine concentration was elevated. The results are consistent with the postulate that the serosal and mucosal membranes of intestinal cells are asymmetrical with respect to amino acid transport mechanisms. The serosal membrane appears to have an Na-independent carrier-mediated mechanism responsible for alanine transport while transport across the mucosal border involves an Na-dependent process.

Sodium movement in high sodium feline red cells

The transport of Na in the cat red cells has been studied under various experimental conditions. The unidirectional radioactive Na influx increased with increasing temperature until it reached a maximum value at 37 degrees C +/- 2 degrees C and then decreased with a further increase in temperature. Errors stated in this paper represent 1.0 standard errors of the mean. The apparent activation energy was calculated in the region between 25 and 37 degrees C and was found to be 4.9 +/- 0.5 kcal/mole. Copper at a concentration of 0.04 mM inhibited this influx by 65%. When cells were suspended in isosmotic KCl buffer, cell volume was found to decrease initially with time. This unusual behavior is discussed in terms of Na to K preference of the cell membrane. In cat red cells, Na influx was found to increase about 13-fold when cell volume was decreased from 1.16 normal to 0.87. This effect could not be reproduced when the medium osmolarity was changed only by the addition of urea, a permeating molecule. On the other hand, K influx was found to decrease from 0.24 +/- 0.03 mEq/liters RBC, hr at a relative cellular volume equal to 1.0 to 0.11 +/- 0.01 mEq/liters RBC, hr at a cell volume of 0.75. Na influx in human red cells did not show any significant dependence on cell volume. The properties of Na movement in the cat red cells are compared to those of human red cells.

Characteristics of the amino acid transport system in the mucosal border of rabbit ileum

The specificity of the neutral amino acid transport system in the brush border was examined by studying the ability of amino acid analogues to inhibit the unidirectional influx of phenylalanine from mucosal solution into the cells. Effects were evaluated in terms of the affinity of various substrates for the amino acid site in the transport system. The affinity of amino acids for the site was proportional to the number of carbon atoms in the side chain. Electron-withdrawing substituents in the ring of phenylalanine increased affinity and electron-releasing groups decreased affinity. Removal of the alpha-amino group from phenylalanine decreased affinity by a factor of approximately 50 and removal of the carboxyl group decreased affinity 12-fold. Effects on affinity of variations in the side chain of the amino acid can be comparable in magnitude to that of the carboxyl group. The effect of sodium ion on the transport system appears to be similar for all compounds tested.

The sodium-alanine interaction in rabbit ileum. Effect of sodium on alanine fluxes

The model of the interaction between Na and alanine at the mucosal border of rabbit ileum has been tested further by examining the efflux of alanine from the cells toward the mucosal solution. Alanine efflux shows a tendency toward saturation as cellular alanine concentration increases and is influenced by cellular Na concentration. A decrease in cell Na concentration causes an increase in the apparent Michaelis constant with little change in maximal efflux rate. Studies on strips of mucosa treated with ouabain or cyanide showed that the direction of net alanine transfer between the cells and the medium is determined by the direction of the Na concentration difference. The cells extrude alanine against a concentration difference when cell [Na] exceeds medium [Na] and accumulate alanine when cell [Na] is less than medium [Na]. The observations are consistent with the model previously suggested involving a transport site that combines with and translocates both Na and alanine, and with the concept that the Na concentration difference between mucosal solution and cytoplasm provides at least part of the energy for active transport of alanine.

The sodium-alanine interaction in rabbit ileum. Effect of alanine on sodium fluxes

The interaction between Na transfer and alanine transfer across the mucosal border of rabbit ileum has been studied further by examining the effect of alanine on Na movement. Studies on strips of mucosa treated with ouabain showed that net Na movements against a Na concentration difference could be caused by a concentration difference of alanine. Na extrusion from mucosal cells was demonstrated when cellular alanine concentration exceeded that in the external medium. Conversely, the cells took up Na against a concentration difference when external alanine concentration was greater than cellular concentration. Unidirectional Na efflux from the cells toward the mucosal solution was increased by loading the cells with alanine. The relation between the increment in Na efflux and alanine efflux was approximately that predicted by the model of Curran et al. (reference 2) for the Na-alanine interaction at the mucosal border of the cells. The results offer further indication that the transport system is reversible and symmetrical.