Phosphorylation of cytosolic phospholipase A2 and the release of arachidonic acid in human neutrophils

Kinases mediating phosphorylation and activation of cytosolic phospholipase A2 (cPLA2) in intact cells remain to be fully characterized. Platelet-activating factor stimulation of human neutrophils increases cPLA2 phosphorylation. This increase is inhibited by PD 98059, a mitogen-activated protein (MAP)/extracellular signal-regulating kinase (erk) 1 inhibitor, but not by SB 203580, a p38 MAP kinase inhibitor, indicating that this action is mediated through activation of the p42 MAP kinase (erk2). However, platelet-activating factor-induced arachidonic acid release is inhibited by both PD 98059 and SB 203580. Stimulation by TNF-alpha increases cPLA2 phosphorylation, which is inhibited by SB 203580, but not PD 98059, suggesting a role for p38 MAP kinase. LPS increases cPLA2 phosphorylation and arachidonic acid release. However, neither of these actions is inhibited by either PD 98059 or SB 203580. PMA increases cPLA2 phosphorylation. This action is inhibited by PD 98059 but not SB 203580. Finally, FMLP increases cPLA2 phosphorylation and arachidonic acid release. Interestingly, while the FMLP-induced phosphorylation of cPLA2 is not affected by the inhibitors of the p38 MAP kinase or erk cascades, both inhibitors significantly decrease arachidonic acid release stimulated by FMLP. SB 203580 or PD 98059 has no inhibitory effects on the activity of coenzyme A-independent transacylase.

Ethyl propionate is more effective and less cytotoxic than methyl tert-butyl ether for topical gallstone dissolution

BACKGROUND & AIMS

Ethyl propionate and isopropyl acetate were identified as gallstone solvents with more favorable physicochemical properties than the currently used solvent methyl tert-butyl ether (MTBE). In this study, their efficacy and toxicity were compared.

METHODS

To compare efficacy, matched stones from 33 patients were subjected to dissolution with each solvent. To evaluate cytotoxicity, jejunal segments of the anesthetized rat were exposed to each solvent or saline; the segments were then perfused with markers for active absorption and passive permeability.

RESULTS

For 23 gallstone sets that dissolved completely with all three solvents, the average dissolution time was shorter with ethyl propionate (38 +/- 8 minutes) than with MTBE (60 +/- 13 minutes) (P = 0.03) or isopropyl acetate (55 +/- 12 minutes) (P < 0.001). Four stones did not dissolve with ethyl propionate, seven with MTBE, and eight with isopropyl acetate. After 2 minutes of exposure to the solvents, the dry weight of the segments decreased by 36% after MTBE but was unchanged after the other two solvents (P < 0.001). MTBE caused more inhibition of active absorption than the other solvents (P < 0.001) and a greater increase in passive permeation (P < 0.03).

CONCLUSIONS

Ethyl propionate and isopropyl acetate are less toxic to the intestinal mucosa than MTBE, and ethyl propionate is more effective for gallstone dissolution.

Transforming growth factor-alpha and epidermal growth factor activate mitogen-activated protein kinase and its substrates in intestinal epithelial cells

The signal transduction pathways of mitogenic stimuli in intestinal epithelial cells are not clearly understood. We report here a possible signaling pathway of two closely related agonists, transforming growth factor-alpha (TGF alpha) and epidermal growth factor (EGF). Both increase thymidine incorporation in the intestinal epithelial cell (IEC) line IEC-6. This increase is dose dependent and inhibited by the tyrosine kinase inhibitors genistein and tyrphostin. The addition of either TGF alpha or EGF to IEC-6 cells also stimulates the activities of the two forms of mitogen-activated protein kinase, p42erk2 MAPK and p44erk1 MAPK, as evidenced by increased incorporation of radiolabeled phosphate in myelin basic protein. The main difference between the MAPK activity levels induced by the two agonists is in the intensity of the response. Maximum TGF alpha-induced stimulation of p42erk2 MAPK activity is 9-fold at 2 ng/ml, while maximum EGF stimulation is only 4.5-fold at 25 ng/ml. These doses correlated closely with the dose required for maximum thymidine incorporation. The activity of the 90-kDa ribosomal S6 kinase, a downstream substrate for activated MAPK, is also enhanced as evidenced by increased incorporation of radiolabeled phosphate in the rsk kinase substrate peptide in IEC-6 cells following stimulation with either TGF alpha or EGF. This increase correlates closely with the stimulus-induced increase in MAPK activity with respect to dose, but the time of increased activity is more prolonged, especially after EGF stimulation. TGF alpha induced the synthesis of both c-Fos and c-Myc, two nuclear substrates for MAPK, and increased c-fos and c-myc message levels as well. However, c-Jun protein and c-jun mRNA were not induced. The increase in IEC-6 cell proliferation in response to TGF alpha and EGF stimulation may then be due, in part, to an increase in immediate early gene expression as a direct result of MAPK and RSK activation.

Stimulation of intestinal Na+/H+ exchange by cell volume changes during fasting and refeeding in rats

Intestinal cell water was studied in rats that have been fasted then refed, two conditions that are known to decrease and increase, respectively, proliferation of the intestinal epithelium. Cell water decreased (15%) during fasting and returned to normal with refeeding. The amiloride-sensitive sodium uptake, which estimates uptake through the Na+/H+ exchange was higher in the ileum than the jejunum, but the jejunal uptake, unlike the ileal, was significantly increased in fasted/refed rats than in normally fed or fasted ones. Osmotic shrinkage of intestinal cells followed by restitution of their cell volume stimulated the Na+/H+ exchange in all of the three groups of animals, but the increase was most prominent in the fasted and the fasted/refed groups. Also, shrinkage of cultured jejunal crypt cells (IEC-6) by a hypertonic solution increased intracellular alkalinization that was inhibited by amiloride. The results provide evidence for a relationship between the change in intestinal cell size, such as that which occurs during fasting/refeeding, and the activation of the Na+/H+ antiport system. This may represent one of the signals that initiates intestinal proliferation in the fasting/refeeding state.

A method to quantitatively compare in vivo the effects of gallstone solvents on intestinal mucosal function: a controlled study comparing mono-octanoin with methyl tert-butyl ether in the rat

During contact dissolution of gallstones, solvents may escape from the gallbladder and damage the intestinal mucosa. In order to compare the extent of this potential injury, we developed a method to objectively quantify the effects of two commonly used cholesterol solvents, methyl tert-butyl ether and mono-octanoin, on mucosal transport function in the rat intestine. Two intestinal segments in each of 184 anesthetized rats were cannulated. Three milliliters of either solvent were instilled in one segment and left for varying periods of time, while saline was instilled in the other as control. The segments were then washed and perfused for 45 min with an isotonic solution containing [3H]polyethylene glycol 4000 (a nonabsorbable reference marker) and either [14C]alpha-aminoisobutyric acid (a marker for active absorption) or [14C]mannitol (a marker for passive permeability). Methyl tert-butyl ether caused more inhibition of alpha-aminoisobutyric acid absorption (64%) than mono-octanoin (48%) and a greater reduction of dry weight per centimeter of the perfused segment (22%) compared with mono-octanoin (10%). Such effects appeared after only 1 min of solvent exposure and did not appreciably increase with longer exposures. Permeation of mannitol increased by 26% after 1 min of exposure to mono-octanoin and by 54% after a similar period of exposure to methyl tert-butyl ether. Longer exposures to both solvents did not seem to cause progressive increases in mannitol permeation. The results indicate that brief exposure of the rat jejunum to either of the two solvents causes a reduction in active transport ([14C]alpha-aminoisobutyric acid absorption), an increase in passive permeability (mannitol permeation), and a loss of mucosal constituents. We conclude that the intestinal mucosa is susceptible to solvent damage and may be used as a selectively sensitive model that can characterize the biological injury of gallstone solvents. The study also suggests that escape of the currently available solvents into the small intestine in patients undergoing contact dissolution of gallbladder stones may cause injury to the small intestine.

Transforming growth factor-alpha increases tyrosine phosphorylation of microtubule-associated protein kinase in a small intestinal crypt cell line (IEC-6)

The small intestinal crypt cell line (IEC-6) is an undifferentiated, untransformed, mitotically active cell used in this study to determine the effect of transforming growth factor-alpha (TGF-alpha) on tyrosine phosphorylation levels of cellular proteins. Thymidine incorporation increased maximally after addition of 2 ng/ml TGF-alpha for 24 h. At the same dose, TGF-alpha induced the tyrosine phosphorylation of proteins with approximate molecular masses of 42, 44, 52, 80, 150 and 175 kDa as shown by Western blots treated with anti-phosphotyrosine antibody. The most intense phosphorylation was seen in the 42 kDa (p42) and 44 kDa (p44) proteins, which were identified as two isoforms of microtubule-associated protein kinase (MAPK). This phosphorylation was seen as early as 5 min post stimulation and was dose dependent. Both p42 and p44 were found in the nucleus after stimulation, although a basal level of unphosphorylated protein was present before stimulation. The observed tyrosine phosphorylation of p42 and p44 was inhibited by genistein, a tyrosine kinase inhibitor, and tyrphostin 23, an epidermal growth factor receptor tyrosine kinase inhibitor. We conclude that MAPK is tyrosine phosphorylated in response to TGF-alpha stimulation of IEC-6 cells.

Role of tyrosine kinase and phosphotyrosine phosphatase in growth of the intestinal crypt cell (IEC-6) line

The roles of gastrin and sodium vanadate in proliferation were examined in cultured IEC-6 cells that are mitotically active and derived originally from jejunal crypts of the rat intestine. Incubation of the cells in the presence of gastrin at a concentration of 250 ng/ml or of sodium vanadate at a concentration of 0.2 mM leads to a 60% increase in cell growth in 24 hr. The stimulated growth in both cases was inhibited by genistein, a tyrosine kinase inhibitor. Incubation in the presence of gastrin and sodium vanadate together produced a small, albeit significant, potentiation of growth of the cells. Gastrin as well as sodium vanadate also promoted the phosphorylation on tyrosine of a similar group of proteins with molecular masses of 42, 45, 52, 60, 78, and 120 kDa. The phosphorylations were rapidly occurring as early as 5 min and lasted for only 15 min. Several proteins were detected in normal IEC-6 cells, including GTPase activating protein, raf1 kinase, phospholipase C gamma-1, and phosphoinositide 3-kinase. The results suggest that gastrin and sodium vanadate induce growth of IEC-6 cells by stimulation of tyrosine kinase and/or inhibition of tyrosine phosphatase. The gastrin and sodium vanadate effects also involve the phosphorylation of a number of proteins, the identities of which are not known at present but may include some of the kinases that are frequently associated with cell growth, such as mitogen-activated protein kinase, raf1 kinase, phosphoinositide 3-kinase, and others.

Enhancement of rat intestinal calcium absorption by vanadate

Vanadate alters intestinal transport and may have a role in regulating cell function. To determine whether it influences calcium absorption, we tested the effects of acute and chronic vanadate administration on calcium absorption using single-pass perfusion of jejunal and ileal segments of the in vivo rat intestine. Acute vanadate administration increased the lumen-to-mucosa and net fluxes of calcium in both the jejunum and ileum. The increase was largely due to an enhancement of the saturable fluxes of calcium and was observed at 10(-4) M concentration of vanadate, but not at higher or lower concentrations of the oxyanion, except at the highest concentration used, 10(-2) M, where calcium absorption was inhibited. Chronic vanadate administration caused, on the other hand, no changes in calcium absorption. We have demonstrated previously that rat intestinal (Na+ + K+)-ATPase is inhibited by vanadate, an effect that could raise cell sodium and increase the efflux of sodium across the brush border membrane. The results suggest that the vanadate enhancement of calcium absorption may be related to an increased entry of calcium into the mucosa, possibly as a result of an augmented exchange through the Na+/Ca+ antiport system. Alternatively, vanadate may influence access to a calcium channel in the mucosal membrane of the intestinal epithelium, leading to the observed increase in absorption.

Reversal by vanadate of the effect of diabetes on intestinal growth and transport

Diabetic changes in small intestinal growth and transport were studied in the rat during the administration of the pentavalent vanadium oxyanion, vanadate. This treatment reversed the effect of diabetes on growth of the intestinal mucosa. It eliminated hyperglycemia and restored the normal rate of absorption of AIB and 3-o-methyl glucose by the intestine. The changes are probably caused by an insulin-like action of vanadate on the intestine.

Effect of chronic vanadate ingestion on amino acid and water absorption in rat intestine

Chronic administration of a relatively low concentration of vanadate to rats causes inhibition of water, alpha-aminoisobutyric acid (AIB) and L-alanine absorption. The mechanism responsible for this inhibition was tested by studying the uptake of alanine in isolated rat intestinal cells. The studies suggest that the vanadate inhibition of amino acid transport is primarily caused by a decreased activity of the Na+-K+ pump, an action that is similar to what is observed when the rat intestine is acutely exposed to vanadate. Vanadate appeared to have no direct effect on the entry of amino acids into the intestinal cell. This was evident by the fact that amino acid uptake by enterocytes of control rats was not different from the uptake by cells of vanadate-treated animals that have an inwardly directed Na gradient artificially created across them. Furthermore, 86RB influx and efflux into and out of intestinal tissues of the vanadate-treated animals were, respectively, decreased and increased as compared to normal control tissues and they were similar to what is observed when the intestine is acutely exposed to ouabain, a known specific inhibitor of the Na+-K+ pump.

Effect of acute and chronic vanadate administration on sugar transport in rat jejunum

Vanadate is known to have an insulin-like action which stimulates sugar transport in some systems like adipocytes and muscle cells, but in other systems it inhibits sugar transport by decreasing the activity of (Na+ +K+)-ATPase. To evaluate whether these two opposing actions may influence sugar transport across the intestine, we studied the effects of acute and chronic vanadate administration on the uptake of glucose, galactose, and 3-O-methylglucose in isolated rat intestinal cells. The sugar uptake measurements were also coupled by determinations of rubidium-86 uptake as a measure of the activity of the Na-K pump. Both acute and chronic vanadate administration reduced rubidium uptake by the cells but the reduction did not uniformly influence the uptake of the three sugars in question which were stimulated by the acute exposure of the cells to vanadate. Glucose uptake was also stimulated by chronic vanadate administration, but the uptakes of galactose and 3-O-methylglucose were respectively unaffected or inhibited by chronic vanadate. The findings suggest that the effect of vanadate on sugar transport is dependent on the net difference between two actions of vanadate: (i) stimulation of a receptor site (possibly an insulin receptor site) in the intestinal cell membrane and (ii) inhibition of the Na-K pump. During acute vanadate exposure, the stimulation of the receptor site was very likely a dominant feature which overwhelms the inhibition of the pump. Chronic exposure to vanadate led, on the other hand, to only a limited degree of stimulation of the receptor site and the inhibition of the Na-K pump became evident in the uptake measurements of galactose and 3-O-methyl-glucose. Glucose uptake, however, was stimulated by chronic vanadate ingestion due, very likely, to an increase in the metabolism of this sugar which occurred only with prolonged exposure of the rat intestine to vanadate.

The nonspecific nature of the vanadate inhibition of rat ileal (NA,K)-ATPase

Vanadate has been suggested as an intracellular regulator of (Na+ + K+)-ATPase. To test this hypothesis we examined the stimulatory and inhibitory effects of vanadate on 86--Rb efflux and influx (measurements of the activity of the Na-pump) in rat ileum under conditions of normal, reduced and increased (Na+ + K+)-ATPase activity. The half maximal stimulation of the Rb efflux and the half maximal inhibition of the Rb influx were not different in the three conditions tested. This suggests that vanadate does not have a regulatory effect on the activity of the Na-K-transport enzyme. The vanadate effect seem rather, to be nonspecific in terms of being unrelated, on a mole per mole basis, to the activity of the (Na+ + K+)-ATPase enzyme.

Effect of vanadate on amino acid transport in rat jejunum

Vanadate has been reported to inhibit (Na+ + K+)-ATPase of many cells and in some systems to stimulate adenylate cyclase. Since intestinal transport is influenced by these enzymes, we studied the effects of varying concentrations of orthovanadate (VO-4) on alanine transport in the in vitro rat jejunum. At the higher concentrations tested (10(-3) and 10(-2) M) vanadate had a ouabainlike action on alanine transport. It decreased the mucosal-to-serosal flux and the influx of alanine into the intestinal epithelium and it caused a reduction of (Na+ + K+)-ATPase activity of basolateral membranes. The relatively lower vanadate concentration of 10(-4) M increased the influx and the efflux of alanine across the mucosal border of the jejunum. The increase was associated with elevation of cyclic AMP in the intestinal mucosa. The studies suggest the presence of a dual action of vanadate on amino acid transport, a stimulatory effect at low concentration, due to increased adenylate cyclase activity, and an inhibitory effect at higher concentrations, due to a decreased activity of (Na+ + K+)-ATPase.

Effects of vanadate on water and electrolyte transport in rat jejunum

The effect of vanadate (orthovanadate, VO4-) on water and ion transport was studied in rat jejunum. Water transport was tested by single-pass perfusion in vivo and ion fluxes by the Ussing-chamber technique in vitro. The results suggest that vanadate has two actions on ion and water transport: At low concentrations (10(-4) M) it causes Cl-, Na+ and water secretion by stimulation of adenylate cyclase; At higher concentrations (10(-3) and 10(-2) M) it decreases net absorption of Na+ and Cl- by inhibition of (Na+ + K+)-ATPase.

Intestinal absorption in the mechanically obstructed rat intestine: protection by prostaglandins

Intestinal obstruction inhibits amino acid absorption. The inhibition, being dependent on the pathological changes of the absorptive epithelium, was considered as an index of injury and measured after varying periods of obstruction and after pretreatment with clindamycin, indomethacin, 16,16-dimethyl-PGE2 or arachidonic acid. A reduction in amino acid uptake was apparent after 2h of obstruction and was increasingly evident after 4, 6 and 18 h. During the late phase (after 6 h), inhibition was partly prevented by pretreatment with clindamycin, but the antibiotic was ineffective during the early phase (within the first 2 h). Bacterial colony counts of luminal contents of rats obstructed for 2 h, were not different from counts obtained in controls, but significantly lower than counts in rats that have been obstructed for 6 h. Pretreatment of rats with 16,16-dimethyl-PGE2 or with arachidonic acid prevented the early inhibitory effects of the obstruction. The findings suggest that the early inhibition in amino acid uptake may be related to metabolic changes that are correctable by the administration of 16,16-dimethyl-PGE2 or of arachidonic acid. The inhibition, during the late phase, is mainly related to an overgrowth of the enteric bacteria.

Effect of ethanol on choline transport in rat jejunum

The effect of ethanol on choline transport across the rat jejunum was studied by intraluminal perfusion in vivo and by influx measurement across the brush-border membrane in vitro. Acute ethanol administration (4 g/kg) through a gastric tube caused an increase in net choline absorption within 1 h. The increase was prevented by pretreatment with pyrazole, an inhibitor of ethanol metabolism. Chronic ethanol administration also caused an increase in choline absorption, the effect being unrelated to the nutritional changes that occur with ethanol ingestion. In contrast, direct instillation of 0.65 M ethanol through the perfusate caused no changes in choline absorption, and the perfusion of a 1.14 M solution even decreased absorption. The in vitro influx of choline across the mucosal membrane of the isolated rat jejunum was also enhanced by pretreatment with ethanol given by gavage 1 h prior to experimentation. Similarly, the ethanol-related increase in the influx rate was inhibited by pyrazole but was unaffected by acetaldehyde or acetate. Like ethanol, pretreatment of rats with methanol stimulated the choline influx rate. The results suggest that ethanol metabolism, rather than the direct effect of ethanol by itself, stimulates the absorption and influx of choline into the rat jejunum. The effect is not produced by the primary metabolites of ethanol, acetaldehyde, or acetate but is very likely related to stimulation by other products of ethanol metabolism.

The effect of stirring of the luminal solution on the protection of the rat intestinal mucosa during ischemic injury

Segments of rat ileum made ischemic for 15 min by occlusion of their mesenteric vessels were intraluminally perfused at slow and rapid rates with Krebs buffer containing O2, O2 + glucose or nitrogen. Mucosal leucine influx was measured at the end of the ischemic period. O2 and O2 with glucose provided protection against the ischemic injury, particularly when the stirring of the luminal solution was increased. Rapid perfusion in the absence of oxygen or glucose also protected the intestine probably by rinsing the ischemic gut of noxious agents.

Leucine absorption after mechanical obstruction of the rat small intestine

Leucine absorption across the mechanically obstructed rat intestine was studied by in vivo and in vitro techniques. It varied between the early (after 2 h) and late (after 18 h) phases of the obstruction. During the early phase there was a reduction in mucosal uptake and in net absorption of the amino acid. At 18 h the inhibition in mucosal uptake was more prominent both above and below the occlusion site but net absorption was only reduced below the obstruction and was relatively unaffected above it. Mannitol and nonmediated leucine absorption were also increased above the obstruction. The findings during the late phase suggest the presence of an increase in leucine permeability across the intestine above the occlusion site. The observed normal rate of net leucine absorption across this segment is thought to be due to enhancement in intestinal diffusion which could be masking the depression in mucosal uptake.

Amino acid influx across the mucosal border of the rat intestine in vivo

The lack of an in vivo method for measuring influx of amino acid into the mucosa has prevented a systematic comparison of characteristics of amino acid influx in vivo with prior in vitro studies. We developed and validated a technique for measuring amino acid influx in vivo. The mucosa is exposed briefly to labelled amino acid perfused luminally at a rapid rate and tissue uptake is measured. The brief exposure period insures that amino acid is confined to the segment. The rapid perfusion rate minimizes concentration of endogenous Na+ in the lumen and permits Na-dependency for alpha-aminoisobutyric acid influx to be demonstrated in vivo for the first time. We also demonstrated the inhibitory effect of K+ and competition by glycine on alpha-aminoisobutyric acid influx in vivo. The saturation kinetics for L-leucine in vivo and in vitro were compared under varying perfusion rates and with and without stirring with air. Under optimal conditions of agitation (rapid perfusion and bubbling with air), the apparent Michaelis constant (Kt) is decreased to be almost equal to that determined under comparable influx conditions in vitro. These studies demonstrate no major difference between characteristics of amino acid transport under more physiologic in vivo conditions as compared with prior in vitro studies.

Segmental tuberculosis of the colon diagnosed by colonoscopy

Segmental tuberculosis of the colon is a rare clinical entity. In the absence of pulmonary or ileocecal involvement, colonic tuberculosis may be difficult to differentiate from neoplasm or Crohn's disease by symptomatic and radiological means. Colonoscopy and biopsy can, however, establish the diagnosis and prevent operative intervention, as indicated in the present report. A patient with a radiologically demonstrated strictured lesion of the sigmoid colon was found at colonoscopy to have several hemorrhagic transverse ulcers ranging in diameter between 1-4.5 cm. Multiple target colonoscopic biopsies, specifically from the ulcer beds, revealed necrotizing granulomas and acid-fast bacilli. Antituberculous chemotherapy produced remarkable symptomatic, radiographic and endoscopic improvements and averted exploratory laparotomy for the establishment of the diagnosis. This case report points out the importance of colonoscopic biopsy as a useful diagnostic modality in this disease.

Effect of ethanol on amino acid absorption across in vivo rat intestine

The acute effect of ethanol on amino acid absorption across the in vivo rat intestine was studied using single-pass continuous perfusion and recirculation techniques. The single-pass steady-state perfusion was used to examine the effect on the entire small intestine and recirculation perfusion to examine the effect on short intestinal segments and to limit ethanol absorption. Unlike the in vitro findings of other investigators, ethanol does not cause inhibition of net amino acid absorption in vivo unless the alcohol is perfused in 2 M or higher concentrations. The inhibition that is observed at these concentrations is very likely due to severe injury and shedding of intestinal cells as evidenced by an increased recovery of DNA in the perfusates. The findings suggest that acute ethanol administration, in concentrations that are comparable to those found in the upper intestines of humans after the ingestion of moderate doses of alcohol, does not have a prominent effect on amino acid absorption across the in situ rat intestine. Under these conditions, the ethanol inhibition of active absorption is masked by enhanced diffusion of the amino acids across the intestine.

Effect of amino acids and dipeptides on ethanol absorption across the rat intestine

Effects of amino acids and dipeptides on ethanol (50 mM) absorption were studied by in vivo perfusion of the rat intestine. All the amino acids and dipeptides tested enhanced the rate of ethanol absorption over that observed with a control solution containing an equimolar concentration of mannitol. The increase in the rate of ethanol absorption can be related to the entry of ethanol with water which accompanies the active absorption of these nutrients. Some amino acids and dipeptides like lysine, tryptophan and glycyl-phenylalanine have an additional stimulatory effect on ethanol absorption which seems unrelated to water movement.

Effect of chronic ethanol consumption on leucine absorption in the rat small intestine

Intestinal absorption of leucine was measured in vivo in rats given ethanol for 7 weeks either through a liquid diet or through drinking water and the results were compared with pair-fed and ad libitum-fed control rats. Total leucine absorption by the entire intestine was not inhibited by ethanol but specific absorption per dry weight of mucosa was increased in the ethanol-fed rats. The intestine of the ethanol-fed rats was shorter and thinner then the ad libitum control rats but its absorptive capacity was maintained by functional adaptation probably by a mechanism similar to that which occurs with semistarvation.

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.