Transport of p-aminohippuric acid, uric acid and glucose in highly purified rabbit renal brush border membranes

Glomerular filtration and saturable absorption of iohexol in the rat isolated perfused kidney

1. The renal handling of iohexol was examined in the rat isolated perfused kidney (IPK) over a perfusate concentration range of 5-20 micrograms ml-1. 2. At a concentration of 5 micrograms ml-1, a ratio of renal clearance over clearance by glomerular filtration (ClR/GF) of 0.63 +/- 0.06 could be determined. This ratio increased until 1.02 +/- 0.06 at 20 micrograms ml-1, indicating that a saturable mechanism is involved in the luminal disappearance of the drug. 3. Pretreatment of the kidneys with polylysine, probenecid or diatrizoate resulted in a significantly enhanced clearance of iohexol, probably due to inhibition of membrane binding. Renal clearance data were fitted to a kinetic model including filtration into the primary urine followed by saturable absorption at the luminal membrane. An absorption constant, KA, of 7.3 +/- 1.3 micrograms ml-1, and a maximum rate of absorption, VA,Max, of 1.4 +/- 0.1 micrograms min-1 were determined. 4. Iohexol accumulated in kidney tissue, reaching a concentration of 2 to 7.5 times the perfusate concentration. In freshly isolated proximal tubular cells and kidney cortex mitochondria, iohexol reduced the uncoupled respiratory rate at a concentration comparable to the highest tissue concentration found in the IPK. 5. In conclusion, iohexol is not only filtered by the kidney but also reabsorbed via a saturable mechanism, which results in tubular accumulation. Intracellularly sequestered iohexol may affect mitochondrial oxidative metabolism. Our results indicate that iohexol is not a true filtration marker.

Classical and channel-like urate transporters in rabbit renal brush border membranes

The precise mechanism by which urate is transported across rabbit renal proximal tubule luminal membranes has not been defined. To determine whether urate flux across this membrane represents simple diffusion or transport on specific carriers, urate uptake was examined in brush border membrane vesicles that were prepared by a Mg+(+)-aggregation technique and then exposed to CuCl2. Na(+)-independent, voltage sensitive urate transport was demonstrated in these Cu+(+)-exposed vesicles. Transport was trans-stimulated by urate and cis inhibited by pyrazinoic acid and oxonate. A small fraction of transported urate and urate in the extravesicular fluid was oxidized to allantoin. Kinetic analysis revealed the presence of two kinetically distinct transporters; a channel-like carrier that was inhibited by pyrazinoic acid and oxonate, and a high-affinity, classical, saturable carrier that was inhibited by higher concentrations of oxonate. These studies provide the first direct evidence for carrier-mediated urate transport in rabbit renal brush-border membranes and demonstrate that the rabbit transporter(s) share a number of properties with the urate uniporter in rat proximal tubule cell membranes.

p-Aminohippurate/2-oxoglutarate exchange in bovine renal brush-border and basolateral membrane vesicles

The transport of the amphiphilic organic anion, p-aminohippurate (PAH), across the luminal (brush-border) and contraluminal (basolateral) membrane of renal proximal tubule cells was studied with membrane vesicles isolated from bovine kidney cortex. On the basis of the enrichment of specific activities of marker enzymes, leucine aminopeptidase and Na+/K(+)-ATPase, brush-border and basolateral membrane vesicles can be obtained from bovine kidneys in reasonably pure form. The uptake of [3H]PAH into both brush-border and basolateral membrane vesicles was trans-stimulated by intravesicular PAH and by 2-oxoglutarate. In the absence of Na+, [3H]PAH/2-oxoglutarate exchange was cis-inhibited by unlabelled 2-oxoglutarate in the medium. In the presence of an inward Na+ gradient, 10 microM 2-oxoglutarate, but no other Krebs cycle derivative, cis-stimulated [3H]PAH uptake, indicating that a Na(+)-coupled dicarboxylate transporter and PAH/2-oxoglutarate exchanger cooperate in both membranes to enhance [3H]PAH uptake. [3H]PAH uptake showed a non-saturable and a saturable component with similar apparent Km values in brush-border and basolateral membranes. Although one negatively charged PAH molecule exchanges with one doubly negatively charged 2-oxoglutarate molecule the exchange was electroneutral. Probenecid inhibited [3H]PAH/2-oxoglutarate exchange in brush-border and basolateral membrane vesicles with indistinguishable kinetics. We conclude that similar or identical PAH transporters are located in brush-border and basolateral membranes of bovine kidney proximal tubule cells. This arrangement seems species-specific since a Na+ gradient plus 2-oxoglutarate caused concentrative [3H]PAH uptake in brush-border membrane vesicles from bovine, but not from rat kidney.

Effect of probenecid on tetraethyl ammonium (TEA) transport across basolateral membrane of rabbit proximal tubule

The effect of probenecid on the transport of tetraethylammonium (TEA) was investigated in rabbit reanal cortical slices in an attempt to ascertain the interaction of organic anion with the organic cation transport system in proximal tubule. Probenecid reversibly inhibited TEA uptake by cortical slices in a dose-dependent manner over the concentration range of 1 and 5 mM. The efflux of TEA was not affected by the presence of 3 mM probenecid. Kinetic analysis indicated that probenecid decreased Vmax without a significant change in Km. Probenecid inhibited significantly tissue oxygen consumption at concentrations of 3 and 5 mM. However, probenecid did not significantly reduce TEA uptake in brush border and basolateral membrane vesicles prepared from renal cortex even at higher concentration of 10 mM. These results indicate that probenecid reduces TEA uptake in cortical slices by inhibiting the tissue metabolism rather than by the interaction with the organic cation transporter.

Na+ and H+ gradient-dependent transport of p-aminohippurate in membrane vesicles from dog kidney cortex

The transport of p-aminohippurate (PAH) was studied in basolateral (BLMV) and brush border membrane vesicles (BBMV) isolated from dog kidney cortex. Imposition of an inwardly directed 100 mN Na+ gradient stimulated the uptake of 50 microM [3H]PAH into BLMV, whereas a pH gradient (pHout = 6.0, pHin = 7.4) only slightly enhanced uptake. The Na+ gradient-dependent uptake of PAH was electroneutral, saturable and sensitive to inhibition by probenecid and several anionic drugs, with (apparent) Km = 0.79 +/- 0.16 mM, Vmax = 0.80 +/- 0.05 nmol/mg protein, 15 sec and Ki for probenecid = 0.08 +/- 0.01 mM. Simultaneous imposition of the pH gradient (outward OH- gradient) and inward Na+ gradient stimulated PAH uptake significantly over that with an Na+ gradient alone. These results are consistent with an Na+ gradient-stimulated PAH/OH- exchange mechanism in the basolateral membrane. In BBMV, PAH uptake could be stimulated by an outwardly directed OH- gradient as well as an inward Na+ gradient. Both gradients could drive PAH transport via a mediated probenecid-sensitive pathway. Na+ gradient-stimulated uptake was electrogenic with a (apparent) Km = 4.93 +/- 0.57 mM, Vmax = 6.71 +/- 0.36 nmol/mg protein, 15 sec and Ki,prob = 0.13 +/- 0.01 mM. The kinetic parameters for PAH/OH- exchange were virtually the same, (apparent) Km = 5.72 +/- 0.49 mM, Vmax = 7.87 +/- 0.33 nmol/mg protein, 15 sec and Ki,prob = 0.16 +/- 0.02 mM. When both the Na+ and pH (outward OH-) gradient were simultaneously imposed an almost twofold stimulation in uptake was observed over that with either an Na+ or pH gradient alone. These results suggested that both gradients stimulate PAH transport in BBMV via the same pathway. However, inhibition experiments with various organic anions showed that the specificities of Na+ and pH gradient-stimulated PAH uptake do not entirely overlap. Thus, our results support a simple transport in BBMV, but it cannot be excluded that two separate pathways are involved.

Excretion of para-aminohippurate in the isolated perfused rat kidney: net secretion and net reabsorption

1. The excretion of para-aminohippurate (PAH) in the isolated perfused rat kidney was examined over a wide range of perfusate PAH concentrations (15 microM to 6 mM). PAH excretion increased steadily over the range of perfusate concentrations, reaching a maximal excretion rate of 3.28 mumol/min at a free-PAH concentration of 6 mM. 2. Tubular transport of PAH was evaluated from the difference between ultrafiltered PAH and excreted PAH. Net PAH secretion was observed at low perfusate free PAH concentrations. Net PAH transport was zero at a perfusate free PAH concentration of 2.1 mM. Above this level there was progressive net reabsorption. 3. Probenecid (2.5 mM) decreased PAH secretion to 18% of the initial value at 129 microM-free PAH (P less than 0.05). Probenecid had no effect on net reabsorption of PAH at high perfusate levels of the anion. 4. Alanine (5 mM) decreased net PAH secretion by 50% at low free PAH concentrations (P less than 0.05) and decreased net PAH reabsorption by 50% at at a free PAH concentration of 6 mM (P less than 0.05). These effects could not be related to effects of PAH, probenecid or alanine on glomerular filtration rate (GFR), vascular resistance or electrolyte excretion. 5. The results confirm the existence and integrity of the proximal tubular organic anion secretory system in the isolated kidney. In addition, net PAH reabsorption occurs at high perfusate levels.

Luminal and peritubular steps in renal transport of p-aminohippurate

Why has the PAH transport system proven so difficult to characterize? The major problems appear to arise in three areas: species differences, differences in methodology, e.g., vesicle preparation techniques, and multiplicity of related transport systems. Species differences are certainly important in some areas, e.g., the luminal membrane where the same investigators have shown the presence of an anion exchanger capable of transporting PAH in rat and dog but not in rabbit. Since all of these species effectively secrete PAH, one must question whether or not the primary luminal component of the PAH secretory system has yet been identified. Other species differences have also been described. For example, the amphibian, Necturus, demonstrates bidirectional organic anion transport, including an uphill luminal step and the urinary bladders of certain species of crustaceans show net reabsorption, whereas the bladders of other species show net secretion of PAH. However, these differences may well prove to be important tools in assessing PAH transport, since amplification of specific pathways and the increased experimental control possible in intact tissue preparations from some of these species, e.g., flounder, snake and amphibian tubules or crustacean urinary bladder, may facilitate resolution of many of the remaining uncertainties. Species differences cannot explain the wide variety of results reported for the basolateral membrane transport step, since many of the conflicting studies were done in the same species. Difficulties inherent in vesicle techniques have been discussed above (Subsection III-A2), and emphasize the need to correlate such data with intact tissue preparations. However, the major source of confusion appears to be related to the ability of PAH to interact with several transport systems, directly or indirectly. Thus, despite the preponderance of evidence showing that the PAH transport system at the basolateral membrane is distinct from those for sulfate, mono- and dicarboxylic acids, acidic amino acids, and uric acid, there remains the real possibility that under physiological conditions: PAH may be a minor substrate for these other systems, substrates for other systems may inhibit PAH transport directly through competition for the PAH carrier or indirectly through competition for the same energy source, and entry of a substrate on one system may trans-stimulate PAH uptake on another. Furthermore, the existence of multiple systems may explain the inability of certain manipulations, e.g., Na gradient dissipation in vivo, to block PAH transport. PAH entry may simply increase via another pathway, e.g., anion exchange.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative requirement for ATP for active transport in isolated renal cells

We investigated the quantitative relationship between cellular ATP concentration and Na+-K+-ATPase activity as measured by ouabain-sensitive 86Rb influx in rabbit proximal renal cells. Cellular ATP was reduced in a stepwise manner by rotenone (10(-7) to 10(-5) M) and was increased by 10 mM adenosine. During these maneuvers, ouabain-sensitive 86Rb influx was linearly related to cellular ATP and did not saturate up to 9.9 mM ATP. In contrast, Na+-K+-ATPase activity in membranes prepared from these cells saturated at 2.0 mM ATP at various sodium (10-100 mM) and potassium (4-100 mM) concentrations. Sodium-dependent phosphate uptake and alpha-methylglucoside (alpha-MG) uptake were both inhibited to a similar degree when cellular ATP was reduced. We conclude that 1) the ATP requirement for saturation of Na+-K+-ATPase is higher in intact renal cells than in the membranes, and 2) the uptake of phosphate and alpha-MG are similarly influenced by reduction in ATP. This effect of ATP on phosphate and AMG uptake is most likely an indirect one and is secondary to changes in the sodium gradient across the cell.

Effects of benzyl alcohol on enzyme activities and D-glucose transport in kidney brush-border membranes

Addition of increasing amounts of benzyl alcohol progressively reduced the steady-state anisotropies of diphenylhexatriene and trimethylammoniumdiphenylhexatriene in brush-border membranes from rat kidney. The decrease in order of membrane lipids, equivalent for 50 mM benzyl alcohol to that produced by a rise in temperature of approx. 6 degrees C, had no effect on the activities of alkaline phosphatase or gamma-glutamyltranspeptidase. On the other hand, benzyl alcohol markedly inhibited the D-glucose uptakes measured in the presence of a 100 mM sodium gradient. For concentrations less than 30 mM, benzyl alcohol reduced the Jmax without significant effects on Km, 22Na+ uptake or the vesicular volume of brush-border preparations. Comparable results were obtained substituting octanol for benzyl alcohol. Our data strongly suggest that, at constant temperature, the D-glucose carrier present in renal brush-border membranes is extremely sensitive to variations in membrane physical state.

Carrier-mediated transport systems of tetraethylammonium in rat renal brush-border and basolateral membrane vesicles

Transport of [3H]tetraethylammonium, an organic cation, has been studied in brush-border and basolateral membrane vesicles isolated from rat kidney cortex. Some characteristics of carrier-mediated transport for tetraethylammonium were demonstrated in brush-border and basolateral membrane vesicles; the uptake was saturable, was stimulated by the countertransport effect, and showed discontinuity in an Arrhenius plot. In brush-border membrane vesicles, the presence of an H+ gradient ( [H+]i greater than [H+]o) induced a marked stimulation of tetraethylammonium uptake against its concentration gradient (overshoot phenomenon), and this concentrative uptake was completely inhibited by HgCl2. In contrast, the uptake of tetraethylammonium by basolateral membrane vesicles was unaffected by an H+ gradient. Tetraethylammonium uptake by basolateral membrane vesicles was significantly stimulated by a valinomycin-induced inside-negative membrane potential, while no effect of membrane potential was observed in brush-border membrane vesicles. These results suggest that tetraethylammonium transport across brush-border membranes is driven by an H+ gradient via an electroneutral H+-tetraethylammonium antiport system, and that tetraethylammonium is transported across basolateral membranes via a carrier-mediated system and this process is stimulated by an inside-negative membrane potential.

Neutral amino acid transport by plasma membrane vesicles of the rabbit choroid plexus

Uptakes of neutral L-amino acids into rabbit choroid plexus apical membrane vesicles were studied using L-[14C]amino acids. Apical membrane vesicles were prepared using Ca2+ precipitation and uptakes of 14C-labeled substrates were measured by a rapid mixing and filtration procedure. Na-dependent, concentrative uptake was observed for proline, histidine and methylaminoisobutyric acid (MeAIB). Phenylalanine and D-glucose uptakes showed no significant Na dependence. Proline uptake was a saturable function of the proline concentration with Jmax 3.5 nmol/(mg min) and Kt 0.3 mM. Competition experiments in the presence of Na indicated that proline and MeAIB are mutually competitive. Proline uptake was also inhibited 25% by phenylalanine, but MeAIB uptake was relatively unaffected. Neither proline nor MeAIB transport was significantly inhibited by glycine. We conclude that proline uptake across rabbit choroid plexus apical membrane vesicles in via an Na-dependent pathway which is shared by MeAIB and, to a minor extent, by phenylalanine, but from which glycine is excluded. Histidine uptake was inhibited by glycine, GABA, phenylalanine, proline and MeAIB. This suggests that histidine may utilize a different pathway in addition to that shared with proline and MeAIB. These transporters should play an active role in the regulation of amino acids in the CSF.

Carrier-mediated transport of amino-cephalosporins by brush border membrane vesicles isolated from rat kidney cortex

The uptake of cephalosporin antibiotics by brush border membrane vesicles isolated from rat renal cortex has been studied by a rapid filtration technique, demonstrating a carrier-mediated transport system for amino-cephalosporins such as cephalexin and cephradine. The antibiotics were taken up into an osmotically reactive intravesicular space. The uptake of cephalexin was saturable (apparent Km2.2 mM), was inhibited by structural analogues and sulfhydryl reagents, and was stimulated by the countertransport effect, although the Na+ gradient did not affect the uptake. This transport system was essentially different from the transport system for p-aminohippurate in brush border membranes. The uptake properties for cephradine in brush border membrane vesicles appeared to be similar to those for cephalexin. The present results suggest the existence of a carrier-mediated transport system for amino-cephalosporins in brush border membranes. This system may be a part of the mechanism of tubular reabsorption of these antibiotics.

Mechanisms of p-aminohippurate transport by brush-border and basolateral membrane vesicles isolated from rat kidney cortex

The uptake of [3H]-labeled p-aminohippurate by brush-border and basolateral membrane vesicles isolated from rat renal cortex has been studied by a rapid filtration technique. Some characteristics of carrier-mediated transport for p-aminohippurate were demonstrated in basolateral membrane vesicles: the uptake was inhibited by probenecid or 4,4'-diisothiocyano-2,2'-disulfonic stilbene (DIDS), was saturable, was stimulated by the countertransport effect, and showed discontinuity in the Arrhenius plot. In contrast, brush-border membrane vesicles failed to display saturability of p-aminohippurate uptake and stimulation by the countertransport effect, although probenecid and DIDS reduced the uptake. Furthermore, p-aminohippurate uptake by brush-border membrane vesicles was influenced more sensitively by alteration in the membrane potential compared with that by basolateral membrane vesicles.

Delineation of sodium-stimulated amino acid transport pathways in rabbit kidney brush border vesicles

We have confirmed previous demonstrations of sodium gradient-stimulated transport of L-alanine, phenylalanine, proline, and beta-alanine, and in addition demonstrated transport of N-methylamino-isobutyric acid (MeAIB) and lysine in isolated rabbit kidney brush border vesicles. In order to probe the multiplicity of transport pathways available to each of these 14C-amino acids, we measured the ability of test amino acids to inhibit tracer uptake. To obtain a rough estimate of nonspecific effects, e.g., dissipation of the transmembrane sodium electrochemical potential gradient, we measured the ability of D-glucose to inhibit tracer uptake. L-alanine and phenylalanine were completely mutually inhibitory. Roughly 75% of the 14C-L-alanine uptake could be inhibited by proline and beta-alanine, while lysine and MeAIB were no more effective than D-glucose. Roughly 50% of the 14C-phenylalanine uptake could be inhibited by proline and beta-alanine; lysine was as effective as proline and beta-alanine, and the effects of pairs of these amino acids at 50 mM each were not cumulative. MeAIB was no more effective than D-glucose. We conclude that three pathways mediate the uptake of neutral L, alpha-amino acids. One system is inaccessible to lysine, proline, and beta-alanine. The second system carries a major fraction of the L-alanine flux; it is sensitive to proline and beta-alanine, but not to lysine. The third system carries half the 14C-phenylalanine flux, and it is sensitive to proline, lysine, and beta-alanine. Since the neutral, L, alpha-amino acid fluxes are insensitive to MeAIB, we conclude that they are not mediated by the classical A system, and since all of the L-alanine flux is inhibited by phenylalanine, we conclude that it is not mediated by the classical ASC system. L-alanine and phenylalanine completely inhibit uptake of lysine. MeAIB is no more effective than D-glucose in inhibiting lysine uptake, while proline and beta-alanine appear to inhibit a component of the lysine flux. We conclude that the 14C-lysine fluxes are mediated by two systems, one, shared with phenylalanine, which is inhibited by proline, beta-alanine, and L-alanine, and one which is inhibited by L-alanine and phenylalanine but inaccessible to proline, beta-alanine, and MeAIB. Fluxes of 14C-proline and 14C-MeAIB are completely inhibited by L-alanine, phenylalanine, proline, and MeAIB, but they are insensitive to lysine. Proline and MeAIB, as well as alanine and phenylalanine, but not lysine, inhibit 14C-beta-alanine uptake. However, beta-alanine inhibits only 38% of the 14C-proline uptake and 57% of the MeAIB uptake. We conclude that two systems mediate uptake of proline and MeAIB, and that one of these systems also transports beta-alanine.

Temperature dependence of solute transport and enzyme activities in hog renal brush border membrane vesicles

The temperature dependence of sodium-dependent and sodium-independent D-glucose and phosphate uptake by renal brush border membrane vesicles has been studied under tracer exchange conditions. For sodium-dependent D-glucose and phosphate uptake, discontinuities in the Arrhenius plot were observed. The apparent activation energy for both processes increased at least 4-fold with decreasing temperature. The most striking change in the slope of the Arrhenius plot occurred between 12 and 15 degrees C. The sodium-independent uptake of D-glucose and phosphate showed a linear Arrhenius plot over the temperature range tested (35-5 degrees C). The behavior of the transport processes was compared to the temperature dependence of typical brush border membrane enzymes. Alkaline phosphatase as intrinsic membrane protein showed a nonlinear Arrhenius plot with a transition temperature at 12.4 degrees C. Aminopeptidase M, an extrinsic membrane protein exhibited a linear Arrhenius plot. These data indicate that the sodium-glucose and sodium-phosphate cotransport systems are intrinsic brush border membrane proteins, and that a change in membrane organization alters the activity of a variety of intrinsic membrane proteins simultaneously.

Na+-dependent transport of tricarboxylic acid cycle intermediates by renal brush border membranes. Effects on fluorescence of a potential-sensitive cyanine dye

The effect of the transport of tricarboxylic acid cycle intermediates on the membrane potential of renal brush border vesicles was studied using fluorescence of the cyanine dye, 3,3'-dipropylthiadicarbocyanine iodide. The behavior of the dye in the preparation was established with valinomycin-induced K+-diffusion potentials; increases in fluorescence were associated with depolarizing conditions. Addition of 1 mm succinate or citrate to membrane/dye suspensions produced transient increases in fluorescence, indicative of a depolarizing event(s) associated with the transport of these substrates. The transient response in fluorescence was Na+ dependent, of greater magnitude under Na+-gradient as compared to Na+-equilibrium conditions, and was a saturable function of substrate concentration. The specificity of the fluorescence response was identical to that obtained from studies of the competitive inhibition of succinate transport by tricarboxylic acid cycle intermediates and analogs We conclude that the major tricarboxylic acid cycle intermediates are transported via a common Na+-dependent transport system in renal brush border membranes.

Specificity of the transport system for tricarboxylic acid cycle intermediates in renal brush borders

Uptake studies employing renal brush border membranes were used to examine the structural specificity of the TCA cycle intermediate transport system. The kinetics of reciprocal inhibition between succinate and citrate revealed these compounds to be transported by a common mechanism. The Michaelis constant for succinate (0.11 mM) was significantly lower than that of citrate (0.28 mM), indicating that the system has a higher affinity for succinate than for citrate. The specificity of the transport system was determined from the relative inhibitory constants of 40 organic acids on the transport of succinate. The results established that the system is highly specific for 4-carbon, terminal dicarboxylic acids in the trans-configuration, including the major intermediates of the TCA cycle. The system is comparatively insensitive to monocarboxylates. Substitution of one of several polar, non-charged residues on the alpha-carbon of succinate permitted interaction of the substrate with the transport system, but substitutions on both the alpha and beta-carbons did not. The structural specificity of the system is fundamentally different from that of the dicarboxylate and tricarboxylate exchange systems of mitochondria. The role of this transport system in the reabsorption of TCA cycle intermediates from the proximal tubule is discussed.

Effects of metabolic intermediates on sugar and amino acid uptake in rabbit renal tubules and brush border membranes

1. The effects of tricarboxylic acid cycle intermediates on the renal transport of alpha-methyl-D-glucoside and alpha-amino-isobutyric acid were examined using separated renal tubules of the rabbit. 2. The effect of citrate on alpha-methyl-D-glucoside and alpha-amino-isobutyric acid uptake was markedly biphasic with maximum stimulation of transport occurring at a citrate concentration of 0.64 mM. Biphasic effects were also apparent for L-malate, succinate, fumarate, alpha-ketoglutarate and oxaloacetate. 3. The route of uptake of alpha-methyl-D-glucoside into separated renal tubules is primarily across the brush border (luminal) membrane. 4. Tricarboxylic acid cycle intermediates produced significant stimulation of renal O2 consumption; however, the effects on O2 consumption were not biphasic suggesting that reduced stimulation of transport at high substrate concentration was not caused by a reduction in the supply of metabolic energy. 5. In purified renal cortical brush border membrane vesicles, citrate and alpha-ketoglutarate inhibited the uptake of alpha-methyl-D-glucoside and alpha-amino-isobutyric acid indicating that inhibition of their transport in respiring renal tubules by high concentrations of tricarboxylic acid cycle intermediates occurs via an effect at the membrane level.

Effects of dibutyryl cyclic AMP on the transport of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid in separated tubules and brush border membranes from rabbit kidney

The effect of dibutyryl cyclic AMP on the transport of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid in separated tubules and purified brush border membranes from rabbit kidney was investigated using a rapid filtration procedure. Dibutyryl cyclic AMP stimulated the uptake of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid by separated renal tubules in agreement iwth prior studies utilizing renal slices (Rea, C. and Segal, S. (1973) Biochim. Biophys. Acta 311, 615--624; Weiss, I.W., Morgan, K. and Phang, J.M. (1972) J. Biol. Chem. 247, 760--764). However, in contrast to previous reports, no preincubation of the tissue with dibutyryl cyclic AMP was required for stimulation of transport to be manifest. Dibutyryl cyclic AMP stimulated oxygen consumption by separated tubules suggesting that stimulation of transport may occur by a linkage with renal oxidative metabolism. Dibutyryl cyclic AMP increased the uptake of alpha-aminoisobutyric acid into purified renal brush border membranes. However the uptakes of alpha-methyl-D-glucoside, proline, leucine and phosphate into brush border membranes were significantly inhibited.