Uptake Of Salts Research Articles

Na:K:2Cl Cotransporter (NKCC) of Intestinal Epithelial Cells: SURFACE EXPRESSION IN RESPONSE TO cAMP

During intestinal chloride secretion, epithelial uptake of salts is accomplished largely by a bumetanide-sensitive Na:K:2Cl cotransporter designated here as NKCC. Using monoclonal antibodies directed against NKCC from the human crypt epithelial cell line, T84, we define its surface localization as a function of cotransporter activation. Immunoelectron microscopy, confocal localization, and selective surface biotinylation studies revealed that the 195-kDa NKCC protein is polarized to the basolateral domain. Following immunoprecipitation, several polypeptides coprecipitated with the 195-kDa cotransporter including two prominent proteins of molecular mass 160 and 130 kDa. Immunoblotting with three distinct anti-NKCC monoclonal antibodies in conjunction with deglycosylation experiments suggested that the 160- and 130-kDa bands represented novel proteins unrelated to the cotransporter. Stimulation of T84 monolayers with cAMP agonists, a condition which elicits chloride secretion and leads to microfilament-dependent NKCC activation, did not significantly increase the number of bumetanide-binding sites and only marginally increased surface expression of the 195-kDa cotransporter available for surface biotinylation. In contrast, cAMP agonist stimulation increased the surface expression of the coprecipitating 160- and 130-kDa proteins approximately 6-fold. The increase in surface 160- and 130-kDa proteins was attenuated by phalloidin preloading the cells, a condition which also prevents activation of NKCC without influencing the activity of other membrane transporters participating in chloride secretion. These studies define the polarized distribution of the NKCC protein on intestinal epithelia, indicate that NKCC may be associated with two other previously unidentified membrane proteins and such association is influenced by the F-actin cytoskeleton.

Irreversible inhibition of hepatic fatty acid salt uptake by photoaffinity labeling with 11, 11-azistearate

In order to have a model compound for detection of proteins involved in transport and metabolism of long-chain fatty acid salts by photoaffinity labeling 11,11-azistearate and 11,11-azi[G-3H]stearate (specific radioactivity 2.78 TBq/mmol) were synthesized. The suitability of 11,11-azi[G-3H]stearate for photoaffinity labeling was demonstrated by incorporation into BSA (bovine serum albumin) and H-FABP (hepatic fatty acid salt-binding protein) of rat liver. Repeated photoaffinity labeling resulted in a clear decrease of the binding capacities of both proteins. Labeling of protein mixtures with 11,11-azi[G-3H]stearate showed that binding proteins for long-chain fatty acid salts interact specifically with this probe. Photoaffinity labeling of isolated hepatocytes using 300 microM 11,11-azistearate in the presence of 100 microM BSA resulted in the irreversible inhibition of the uptake of stearate and its analogue 2,2,3,3,18,18,18-heptafluorostearate nearly to the same extent of about 30%. Irreversible inhibition of the uptake of long-chain fatty acid salts by photoaffinity labeling did not alter the mediated transport of cholyltaurine and has no effect on the uptake of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, a compound that crosses the hepatocyte membrane by simple diffusion. The irreversible inhibition of membrane transport by photoaffinity labeling demonstrates the existence of a specific transport system for the uptake of long-chain fatty acid salts into hepatocytes.

Brief pre- and post-irrigation sprinkling with fresh water reduces foliar salt uptake in maize and barley sprinkler irrigated with saline water

Brief pre- and post-irrigation sprinkling treatments using freshwater were tested to determine if these practices could reduce the uptake of salts through leaves when saline water is used to sprinkler irrigate crops. Maize and barley were sprinkler irrigated 2 to 3 times per week for 30 min with saline water (4.2 dS m−1, 30 mmol L−1 NaCl and 2.8 mmoles L−1 CaCl2 for maize and 9.6 dS m−1, 47 mmoles L−1 NaCl and 23.5 mmoles L−1 CaCl2 for barley) in separate experiments with plants grown in pots outdoors. The soil surface of all pots was covered to prevent salinization of the soil by the sprinkling water. One half of the sprinkled plants was grown in nonsaline soil to study the effects of pre-wetting and post-washing when ion uptake was primarily through leaves. The other half of the sprinkled plants was grown in soil salinized by drip irrigation, in order to evaluate the effects of pre-wetting and post-washing when Na+ and Cl- uptake was through both leaves and roots. Post-washing with freshwater (5 min) reduced the leaf sap concentrations of Cl- in saline-sprinkled plants from 56 to 43 mmol L−1 in maize and from 358 to 225 mmol L−1 in barley (averages for plants grown in nonsaline and saline soil). Na+ concentrations in leaf sap were reduced from 93 to 65 mmoles L−1 (maize) and from 177 to 97 mmoles L−1 (barley) by the post-washing. Pre-wetting had a small effect on ion uptake through leaves, the only significant reduction in seasonal means being in leaf Na+ concentrations for plants grown in nonsaline soil. Pre-wetting and post-washing, when combined, reduced leaf Cl- concentrations to levels similar to those of nonsprinkled plants grown in saline soil; however, Na+ concentrations in leaves remained 3.5 times (maize) and 1.5 times (barley) higher than those of nonsprinkled plants. When pre-wetting and post-washing were not applied, sprinkled barley plants grown in saline soil had grain yields which were 58% lower than nonsprinkled plants grown in saline soil, but the reduction in grain yield was only 17% when the freshwater treatments were given. We conclude that a brief period of post-washing with freshwater is essential when saline water is employed in sprinkler irrigation. By comparison, the benefits from pre-wetting were small in these experiments. ei]T J Flowers

Disturbances of Potassium Homeostasis in Poisoning

Unless renal function is impaired or rhabdomyolysis is severe, hyperkalemia is a relatively uncommon metabolic complication of poisoning. In contrast, marked hypokalemia is a more common problem and may have serious sequelae. Most potassium disturbances in acute poisoning are due to disruption of extra-renal control mechanisms, notably the activity of Na+/K+ ATPase and K+ channels. Hypokalemia occurs because of increased Na+/K+ ATPase activity (e.g. beta 2 agonist, theophylline or insulin poisoning), competitive blockade of K+ channels (e.g. barium or chloroquine poisoning), gastrointestinal losses and/or alkalosis. Hyperkalemia follows inhibition of Na+/K+ ATPase activity (e.g. by digoxin), increased uptake of potassium salts, disruption of intermediary metabolism (e.g. cyanide poisoning), activation of K+ channels (e.g. fluoride poisoning), and the presence of acidosis and rhabdomyolysis, particularly if the latter is complicated by renal failure. Hypokalemia results in generalized muscle weakness, paralytic ileus, ECG changes (flat or inverted T waves, prominent U waves, ST segment depression) and cardiac arrhythmias (atrial tachycardia +/- block, AV dissociation, VT, VF). Hyperkalemia is associated with abdominal pain, diarrhea, muscle pain and weakness, ECG changes (tall peaked T waves, ST segment depression, prolonged PR interval, QRS prolongation) and cardiac arrhythmias (VT, VF). Significant disturbances of potassium homeostasis are often unrecognized and may cause considerable morbidity and mortality. Prompt recognition and appropriate treatment of these disturbances could be life-saving.

Cholestasis caused by inhibition of the adenosine triphosphate-dependent bile salt transport in rat liver

Background/Aims: Inhibition of bile salt transport across the hepatocyte during cholestasis induced by cyclosporin A has been shown. However, the contribution of the different bile salt transport systems in liver to cholestasis has remained controversial. Methods: The sensitivity of different bile salt transport systems in liver to cyclosporin-induced inhibition was determined by transport assays in plasma membrane vesicles and by in vivo studies in the rat. Results: Cyclosporin A-induced inhibition of sodium-dependent uptake of bile salts across the sinusoidal membrane, of potential-dependent, and of adenosine triphosphate (ATP)-dependent bile salt transport across the canalicular membrane exhibited inhibition constants (Kl) of 5, 70, and 0.2 μmol/L, respectively. The nonimmunosuppressive cyclosporin analogue PSC 833 also preferentially inhibited the ATP-dependent bile salt transport with an inhibition constant of 0.6 μmol/L. Cyclosporin A and its analogue PSC 833 [(3′-oxo-4-butenyl-4-methyl-Thr1)-(Val2)-cyclosporin] (25 mg/kg each) served as tools to interfere with [14C]taurocholate secretion into bile in vivo, causing an accumulation of [14C]-taurocholate taurocholate in liver and reducing bile flow to 50%. In mutant rats deficient in the transport of leukotriene C4 and related conjugates across the canalicular membrane, bile flow was reduced to 14%. Conclusions: The cyclosporins preferentially inhibit the ATP-dependent bile salt export carrier in the canalicular membrane. This inhibition reduces bile salt-dependent bile flow and causes intrahepatic cholestasis.

Osmoregulation in the stenohaline freshwater catfish, Heteropneustes fossilis (Bloch) in deionized water

Transfer of the stenohaline catfish, Heteropneustes fossilis from tap water (TW) to deionized water (DW) resulted in an increase in the glomerular filtration rate, urine volume and osmolar and free water clearance. In a closed system, where the DW was renewed only once a day, no change in the plasma osmolality was evident for up to 14 days. When DW was renewed four times a day for 25 days, a significant reduction in the plasma osmolality was observed within 24h. When the fish were transferred back to TW, plasma osmolality increased to normal freshwater level within 24h. These observations suggest the existence of highly efficient branchial mechanisms for active uptake of salts from an exceedingly dilute ambient medium. The fact that prolactin-secreting cells as well as corticotrophs in the pituitary of the fish in DW were highly stimulated suggests the involvement of the hormones in the adaptive responses of the catfish to DW.

Cellular uptake of titanium and vanadium from addition of salts or fretting corrosion in vitro

The use of titanium and titanium-6% aluminum-4% vanadium alloy for dental and orthopedic implants has increased in the last decade. The implants are presumed to be compatible because osseointegration, bony apposition, and cell attachment are known. However, the cellular association of titanium and vanadium have remained unknown. This study examined the uptake of salts or fretting corrosion products. Titanium was not observed to be toxic to the cells. Vanadium was toxic at levels greater than 10 micrograms/mL. The percentage of cellular association of titanium was shown to be about 10 times that of vanadium. The percentage of cellular association of either element was greater from fretting corrosion than from the addition of salts. The presence of vanadium did not affect the cellular uptake of titanium. The presence of titanium decreased the cell association of vanadium.

Role of sodium ions for sulfate transport and energy metabolism in Desulfovibrio salexigens

The sodium ion gradient and the membrane potential were found to be the driving forces of sulfate accumulation in the marine sulfate reducer Desulfovibrio salexigens. The protonmotive force of −158 mV, determined by means of radiolabelled membrane-permeant probes, consisted of a membrane potential of −140 mV and a pH gradient (inside alkaline) of 0.3 at neutral pHout. The sodium ion gradient, as measured with silicone oil centrifugation and atomic absorption spectroscopy, was eightfold ([Na+]out/[Na+]in) at an external Na+ concentration of 320 mM. The resulting sodium ionmotive force was −194 mV and enabled D. salexigens to accumulate sulfate 20000-fold at low external sulfate concentrations (<0.1 μM). Under these conditions high sulfate accumulation occurred electrogenically in symport with three sodium ions (assuming equilibrium with the sodium ion-motive force). With increasing external sulfate concentrations sulfate accumulation decreased sharply, and a second, low-accumulating system symported sulfate electroneutrally with two sodium ions. The sodium-ion gradient was built up by electrogenic Na+/H+ antiport. This was demonstrated by (i) measuring proton translocation upon sodium ion pulses, (ii) studying uptake of sodium salts in the presence or absence of the electrical membrane potential, and (iii) the inhibitory effect of the Na+/H+ antiport inhibitor propylbenzilylcholin-mustard HCl (PrBCM). With resting cells ATP synthesis was found after proton pulses (changing the pH by three units), but neither after pulses of 500 mM sodium ions, nor in the presence of the uncoupler tetrachorosalicylanilide (TCS). It is concluded that the energy metabolism of the marine strain D. salexigens is based primarily on the protonmotive force and a protontranslocating ATPase.

A new bile acid transporter?

Transport systems involved in uptake and biliary secretion of bile salts have been extensively studied in rat liver; however, little is known about these systems in the human liver. In this study, we investigated taurocholate (TC) transport in canalicular and basolateral plasma membrane vesicles isolated from 15 human livers (donor age 6–64 yr). ATP stimulated the uptake of TC into both canalicular and basolateral human liver plasma membrane vesicles (cLPM and bILPM, respectively). Considerable interindividual variations in the transport velocity were observed in the different membrane preparations used: 9.0 ± 1.3 (mean ± SEM, n = 17; range 1.6–18.0) and 9.3 ± 2.0 (range 1.1–29.8) pmol TC · protein−1 · min−1 at 1.0 μM TC for cLPM and bILPM, respectively. TC transport was temperature sensitive and showed saturation kinetics with a high affinity for TC (Km 4.2 ± 0.7 μM and 3.7 ± 0.5 μM for cLPM and bILPM, respectively). Transport was dependent on the ATP concentration and saturable (Km 0.25 ± 0.03 mM, n = 3). Neither nitrate, which reduces membrane potential, nor the protonophore FCCP strongly inhibited ATP-dependent TC transport, indicating that membrane potential and proton gradient are not involved in this process. TC transport was significantly inhibited by the classical anion transport inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulfonate (250 μM) and the glutathione conjugate S-(2,4-dinitrophenyl)glutathione (100 μM). In conclusion, high affinity ATP-dependent TC transport is present in human liver at both the canalicular and the basolateral sides of the hepatocyte.

Electrogenicity of Na-coupled bile salt transport in isolated rat hepatocytes.

The importance of membrane voltage in uptake of bile salts into hepatocytes is not known. Electrogenicity of the primary bile salt transport process, Na-bile salt cotransport, has been difficult to determine because the large K and Cl conductances of the sinusoidal membrane (GK and GCl, respectively) obscure any transport associated currents. In the present study hepatocytes were treated to reduce these membrane conductances and electrogenic entry of taurocholate and glycocholate was demonstrated. Intracellular voltage and resistance changes resulting from bile salt transport were measured in hepatocytes in which GK and GCl were blocked by impalement with Na acetate microelectrodes and external exposure to quinine (400 microM). This increased the cell input resistance from 153 +/- 17 to 230 +/- 17 M omega (n = 14, P < 0.001). Under these conditions, exposure to 100 microM of taurocholate or glycocholate produced Na-dependent depolarizations of 3.0 +/- 0.5 and 4.2 +/- 0.8 mV, respectively. These correspond to transport currents of 13.9 and 7.6 pA/cell, which are comparable to those predicted from known [3H]taurocholate uptake rates if one positive charge enters the cell with each bile salt molecule. Although uptake of these two bile salts was electrogenic, this was not the case for all bile salts. Na-dependent transport of taurodehydrocholate, which occurs at similar rates to that for taurocholate, produced no voltage change. The unconjugated bile salts cholate and ursodeoxycholate also produced no measurable voltage or resistance changes. In conclusion, Na-dependent uptake of taurocholate and glycocholate is electrogenic, whereas uptake of taurodehydrocholate, ursodeoxycholate, and cholate is predominantly electroneutral.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescent derivatives of bile salts. III. Uptake of 7 beta-NBD-NCT into isolated hepatocytes by the transport systems for cholyltaurine

Uptake of 7 beta-NBD-NCT ([N-[7-(4-nitrobenzo-2-oxa-1,3-diazol)]-7 beta-amino-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oyl)-2'-aminoethanesulfonate) in isolated rat liver hepatocytes occurs by saturable transport without being superimposed by simple diffusion. The dependency of flux rate of uptake on the concentration of 7 beta-NBD-NCT in the presence of Na+ (143 mM) and with Na+ depletion (1 mM) is best described by the assumption of two simple transport systems. Maximal flux rates of uptake Jn and half-saturation constants KT for 7 beta-NBD-NCT are in presence of Na+ for transport system 1 J1(Na+ 143) = 0.15 +/- 0.03 nmol/(min.mg protein) and KT1(Na+ 143) = 3.5 +/- 0.5 microM and for transport system 2 J2(Na+ 143) = 1.0 +/- 0.1 nmol/(min.mg protein) and KT2(Na+ 143) = 190 +/- 25 microM, and in case of Na+ depletion J1(Na+ 1) = 0.1 +/- 0.03 nmol/(min.mg protein), KT1(Na+ 1) = 3.0 +/- 0.5 microM, and J2(Na+ 1) = 0.85 +/- 0.9 nmol/(min.mg protein) and KT2(Na+ 1) = 195 +/- 27 microM. Uptake of 7 beta-NBD-NCT by both transport systems is competitively inhibited by cholyltaurine in the presence of Na+ and with Na+ depletion. Two transport systems are likewise involved in the uptake of cholyltaurine in the presence of Na+ as well as in case of Na+ depletion. Their kinetic parameters are in presence of Na+ J'1(Na+ 143) = 1.55 +/- 0.14 nmol/(min.mg protein) and K'T1(Na+ 143) = 16.1 +/- 3.0 microM, and J'2(Na+ 143) = 0.51 +/- 0.05 nmol/(min.mg protein) and K'T2(Na+ 143) = 38.0 +/- 4.1 microM, and in case of Na+ depletion J'1(Na+ 1) = 0.10 +/- 0.02 nmol/(min.mg protein), K'T1(Na+ 1) = 7.7 +/- 1.2 microM, and J'2(Na+ 1) = 0.40 +/- 0.03 nmol/(min.mg protein) and K'T2(Na+ 1) = 41.0 +/- 4.2 microM. Uptake of cholyltaurine by both transport systems is competitively inhibited by 7 beta-NBD-NCT in the presence of Na+ as well as in case of Na+ depletion. In both cases the inhibition constants are practically identical with the KT values for uptake of 7 beta-NBD-NCT. Photoaffinity labeling of isolated hepatocytes using 7,7-ACT (400 microM) resulted in the irreversible inhibition of uptake of both bile salts to similar extents, confirming the kinetic data that 7 beta-NBD-NCT is a true analogue of cholyltaurine.

Electroneutral uptake and electrogenic secretion of a fluorescent bile salt by rat hepatocyte couplets

The role of membrane voltage as a driving force for the hepatic uptake and secretion of fluorescent bile salts has been examined in isolated hepatocyte couplets. The present study demonstrates that the fluorescent bile salt derivative (N-[7-(nitrobenz-2-oxa- 1,3-diazol-4-yl)]-7-amino-3 alpha, 12 alpha-dihydroxy-5-cholan-24-oyl)-2-aminoethanesulfonate (7 beta-NBD-NCT) is taken up into hepatocytes by a saturable process with a Kt of 2.7 microM. Uptake rate was reduced by only 22% after total Na+ replacement and was independent of transmembrane potential difference over a range of -135 to +25 mV. In contrast, secretion into the canalicular space was strongly dependent on membrane voltage over the range from -34 to 0 mV in a manner consistent with electrodiffusion of an anion. Fitting the secretion time course to that predicted by electrodiffusion demonstrated that only approximately 50% of total secretion can result from electrodiffusion. Studies in isolated perfused liver confirmed this observation that depolarization caused a decrease in bile salt secretion rate. These results demonstrate that 7 beta-NBD-NCT is transported by a neutral uptake process at the sinusoidal membrane and is secreted across the canalicular membrane in part by electrogenic transport. This suggests that voltage changes could be a common pathway resulting in impaired organic anion secretion in diverse cholestatic syndromes.

Adenosine triphosphate-dependent taurocholate transport in human liver plasma membranes.

Transport systems involved in uptake and biliary secretion of bile salts have been extensively studied in rat liver; however, little is known about these systems in the human liver. In this study, we investigated taurocholate (TC) transport in canalicular and basolateral plasma membrane vesicles isolated from 15 human livers (donor age 6-64 yr). ATP stimulated the uptake of TC into both canalicular and basolateral human liver plasma membrane vesicles (cLPM and blLPM, respectively). Considerable interindividual variations in the transport velocity were observed in the different membrane preparations used: 9.0 +/- 1.3 (mean +/- SEM, n = 17; range 1.6-18.0) and 9.3 +/- 2.0 (range 1.1-29.8) pmol TC.mg protein-1.min-1 at 1.0 microM TC for cLPM and blLPM, respectively. TC transport was temperature sensitive and showed saturation kinetics with a high affinity for TC (Km 4.2 +/- 0.7 microM and 3.7 +/- 0.5 microM for cLPM and blLPM, respectively). Transport was dependent on the ATP concentration and saturable (Km 0.25 +/- 0.03 mM, n = 3). Neither nitrate, which reduces membrane potential, nor the protonophore FCCP strongly inhibited ATP-dependent TC transport, indicating that membrane potential and proton gradient are not involved in this process. TC transport was significantly inhibited by the classical anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonate (250 microM) and the glutathione conjugate S-(2,4-dinitrophenyl)glutathione (100 microM). In conclusion, high affinity ATP-dependent TC transport is present in human liver at both the canalicular and the basolateral sides of the hepatocyte.

Subcellular and Molecular Mechanisms of Bile Secretion

One of the liver's principal functions is the formation of bile, which is requisite for digestion of fat and elimination of detoxified drugs and metabolites. Bile is a complex fluid made up of water, electrolytes, bile acids, pigments, proteins, lipids, and a multitude of chemical breakdown products. In this review, we have summarized the source of various biliary components, the route by which they end up in bile, including the underlying subcellular and molecular mechanisms, and their contribution to bile formation. One of the reasons why bile formation is so complex is that there are many mechanisms with overlapping substrate specificities, i.e., many biochemically unrelated biliary constituents share common transport mechanisms. Additionally, biliary constituents may reach bile by more than one pathway. Some biliary components are critical for bile formation; others are of minor significance for bile formation but play a major physiological role. The major driving force for bile formation is the uptake and transcellular transport of bile salts by hepatocytes. The energy for bile formation comes from the sodium gradient created by the basolateral Na+/K(+)-ATPase, to which bile salt transport is coupled. The secretory pathway for bile salts involves uptake at the basolateral surface of the hepatocyte, vectorial transcellular movement, and transport across the canalicular membrane into the canalicular lumen. Hydrophilic bile salts are taken up via a sodium-dependent, saturable, carrier-mediated process coupled to the Na+/K(+)-ATPase. This uptake mechanism is also shared by other substrates, such as electroneutral lipids, cyclic oligopeptides, and a wide variety of drugs. Hydrophobic bile acids are taken up by a sodium-independent facilitated carrier-mediated mechanism in common with other organic ions, including sulfated bile acids, sulfobromophthalein, bilirubin, glutathione, and glucuronides, or by nonsaturable passive diffusion. Two major carrier proteins have been identified on the hepatocyte basolateral membrane: a 48-kDa protein that appears to be involved with Na(+)-dependent bile salt uptake, and a 54-kDa protein, thought to be associated with Na(+)-independent bile salt uptake. The intracellular transport of bile salts may involve cytosolic carrier proteins, of which several have been identified. Some evidence suggests a vesicular transport mechanism for bile salts. Since bile acids clearly do not enter the cell by endocytosis, formation of transport vesicles must be a more distal event in the transcellular translocation process. Some bile salts appear to be transported within the same unilamellar vesicles that are involved in the secretion of cholesterol and phospholipid.(ABSTRACT TRUNCATED AT 400 WORDS)

Tooth enamel softening with a cola type drink and rehardening with hard cheese or stimulated saliva in situ

The in-situ remineralization effect of hard cheese was compared with that of saliva on tooth enamel in man. The intra-oral test of softening enamel surfaces by a cola type drink followed by rehardening by chewing hard cheese and/or parafilm was assessed by microhardness and SEM measurements. Cheese consumption significantly increased the enamel hardness, whereas stimulated saliva did not have this effect. The remineralizing effects are presumably due to uptake of calcium and phosphate salts by the surface enamel. Morphologically, the enamel surfaces did not return to their original state.

Effect of high external NaCl concentrations on ion transport within the shoot of Lupinus albus. I. Ions in xylem sap

Abstract. Xylem sap was collected from individual leaves of intact transpiring lupin plants exposed to increasing concentrations of NaCl by applying pneumatic pressure to the roots. Concentrations of Na+ and Cl− in the xylem sap increased linearly with increases in the external NaCl concentration, averaging about 10% of the external concentration. Concentrations of K+ and NO3−, the other major inorganic ions in the sap, were constant at about 2.5 and 1.5 mol m−3, respectively. There was no preferential direction of Na + or Cl− to either young or old leaves: leaves of all ages received xylem sap having similar concentrations of Na+ and Cl−, and transpiration rates (per unit leaf area) were also similar for all leaves. Plants exposed to 120–160 mol m−3 NaCl rapidly developed injury of oldest leaves; when this occurred, the Na+ concentration in the leaflet midrib sap had increased to about 40 mol m−3 and the total solute concentration to 130 osmol m−3. This suggests that uptake of salts from the transpiration stream had fallen behind the rate of delivery to the leaf and that salts were building up in the apoplast.

The relationship between lipophilic-hydrophilic balance, uptake and anti-bacteriophage lambda activity of experimental anti-tumour bisquaternary salts

The uptake by Escherichia coli of a series of bisquaternary experimental anti-tumour agents (quinolinium 4-[ p-9(-pyridylamino)phenylcarbamoyl]-anilinebisalkyl dibromides) has been measured both by association of radiolabelled compounds and their inhibition of the vegetative replication of bacteriophage λ (after heat inactivation of the phage repressor) as a measure of biologically effective intracellular drug concentration. Uptake of these compounds was correlated with biological effect, and was a function of both incubation temperature and the lipophilic-hydrophilic balance of the compound. At 30°C uptake was drug concentration-dependent and was not readily reversible. No saturation of uptake was apparent over the concentration range tested. Preliminary experiments indicated that time-dependent drug uptake was also related to growth inhibition in cultured L1210 murine leukaemia cells. These results are consistent with the hypothesis that uptake occurs by diffusion across the plasma membrane followed by strong binding to cell constituents such as DNA. The approximate range of uptake of the most active compounds, using an external drug concentration of 1 μM, are 100 and 2400 molecules/s respectively for bacteria and murine leukemia cells. For bacteria, the uptake of approx. 2 × 10 5 molecules of drug/cell inhibits the yield of phage λ by 90%.

Preliminary Comparison of Dry Weight Increase with Short-Term Uptake of C, N and P in Cultured Chara hispida Plants

The uptake of inorganic salts of carbon, nitrogen and phosphorus is compared with the dry weight increase in Chara hispida plants which were cultured under conditions that support high rates of growth. The dry mass of 4 to 6 week-old plants contained 23 ± 0.9% carbon, 2.2 ± 0.27 % nitrogen and 0.5 ± 0.04 % phosporus. The rates of nutrient uptake required for the observed increase in dry weight are in agreement with the uptake measured over short periods in separate experiments.

Transport systems for amphipathic compounds in normal and neoplastic hepatocytes

Photoaffinity labeling of plasma membrane subfractions from liver and of intact liver tissue with a photolabile bile salt derivative, the sodium salt of (7,7-azo-3α,12α-dihydroxy-5β-cholan-24-oyl)-2-aminoethanesulfonic acid, revealed that the hepatobiliary transport of bile salts is accomplished by transport systems different for sinusoidal uptake and canalicular secretion. Polypeptides with apparent M r values 54,000 and 48,000 interact with bile salts at sinusoidal membrane, whereas a polypeptide with an apparent M r of 100,000 is involved in bile salt secretion through the canalicular membrane. Photoaffinity labeling with photolabile derivatives of uncharged and cationic compounds provided evidence that the sinusoidal membrane polypeptides exhibit a broad binding specificity. Photoaffinity labeling studies and kinetic studies suggest that hepatic uptake of different amphipathic anions, uncharged compounds and even of cations is mediated by the sinusoidal transport systems which are involved in the uptake of bile salts. Relatively little is known about the specificity of the canalicular bile salt transport system. The fluorescent bile salt derivative, the sodium salt of { N-[7-(4-nitrobenzo-2-oxa-1,3-diazol)]-3 β-amino-7 α,12 α-dihydroxy-5 β-cholan-24-oyl}-2- aminoethanesulfonic acid, is readily taken up into the hepatocytes of all acinar zones and may be used for the evaluation of the functional state of bile salt transport by fluorescence microscopy. Fluorescent microscopic studies with the fluorescent bile salt derivative showed that ascites hepatoma AS 30D cells do not have the ability to take up bile salts and demonstrated the absence of hepatobiliary bile salt transport in the solid Morris hepatoma 7777. Photoaffinity labeling studies revealed that in both tumor cell models, in hepatoma AS 30D and in Morris hepatoma 7777, the plasma membranes were devoid of the polypeptides having affinities to bile salts and amphipathic cations. A slight labeling of bile salt binding membrane polypeptides in plasma membranes from Morris hepatomas 9618A and TC 5123 opens the possibility to study transport in neoplastic hepatocytes.

Studies into the differential activity of the hydroxybenzonitrile herbicides: II. Uptake, movement and metabolism in two contrasting species

Uptake, movement, and metabolism of unformulated ioxynil and bromoxynil salts were investigated in Matricaria inodora and Viola arvensis. The morphology of these two species did not give rise to different spray retention and contact angles. After 7 days, uptake of [ 14C]ioxynil-Na reached 8.26% of applied 14C activity in M. inodora and 16.77% of that in V. arvensis compared with 1.54 and 3.83%, respectively, for [ 14C]bromoxynil-K. Over 98% of the 14C activity detected in the plant after 7 days remained in the treated leaves of V. arvensis following [ 14C]ioxynil-Na treatment. However, 8.7% of the 14C activity detected in [ 14C]ioxynil-Na-treated M. inodora was recovered from the apex and developing leaves reflecting a greater translocation. [ 14C]Bromoxynil-K was more mobile in both species and after 7 days 87.5 and 91.39% were detected in the treated leaves of M. inodora and V. arvensis, respectively. In both species the majority of translocated 14C activity was recovered from the apex and developing leaves. Up to 20% of the applied [ 14C]ioxynil-Na and [ 14C]bromoxynil-K was not detected within the treated plant. Extraction of treated plants revealed no detectable metabolic breakdown of ioxynil-Na to halogenated derivatives in either species. However, metabolic breakdown of bromoxynil-K was apparent in V. arvensis. No significant root exudation was detected when [ 14C]ioxynil-Na and [ 14C]bromoxynil-K were applied to hydroponically grown S. media and V. arvensis. Losses of 14C activity were due to herbicide volatility or degradation to volatile products on the leaf surface.