Gamma-glutamyl transpeptidase in the urine from an isolated rabbit kidney perfused with and without DMSO

Chloroquine, a novel inhibitor of amino acid transport by rat renal brush border membrane vesicles

Chloroquine is an antimalarial and antirheumatic lysosomotropic drug which inhibits taurine uptake into and increases efflux from cultured human lymphoblastoid cells. It inhibits taurine uptake by rat lung slices and affects the uptake and release of cystine from cystinotic fibroblasts. Speculations on its mode of action include a proton gradient effect, a non-specific alteration in membrane integrity, and membrane stabilization. In this study, the effect of chloroquine on the uptake of several amino acids by rat renal brush border membrane vesicles (BBMV) was examined. Chloroquine significantly inhibited the secondary active, NaCl-dependent component of 10µM taurine uptake at all concentrations tested, but did not change equilibrium values. Analysis of these data indicated that the inhibition was non-competitive. Taurine uptake was reduced at all osmolarities tested, but inhibition was greatest at the lowest osmolarity. Taurine efflux was not affected by chloroquine, nor was the NaCl-independent diffusional component of taurine transport. Chloroquine (1 mM) inhibited uptake of the imino acids L-proline and glycine, and the dibasic amino acid L-lysine. It inhibited the uptake of D-glucose, but not the neutralα-amino acids L-alanine or L-methionine. Uptake of the dicarboxylic amino acids, L-glutamic acid and L-aspartic acid, was slightly enhanced. With regard to amino acid uptake by BBMV, these findings may support some of the currently proposed mechanisms of the action of chloroquine but further studies are indicated to determine why it affects the initial rate of active amino acid transport.

The differential diagnostic value of urinary enzyme and amino acid excretion in children with nephrotic syndrome

Urinary enzymes N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transpeptidase (gamma-GT) are sensitive markers of specific renal cell damage. Excessive urinary amino acid excretion may also be an indicator of renal tubular damage. We have evaluated urinary excretion of NAG, gamma-GT and 37 amino acids, phospholipids and dipeptides in 30 children (aged 2.3-18.1 years) with nephrotic syndrome (NS), 23 with minimal change nephrotic syndrome (MCNS), 7 with focal segmental glomerulosclerosis (FSGS) and 16 healthy age-matched controls. Nine MCNS patients were in relapse and 14 in remission. Enzyme activity is expressed as micromoles per milligram urinary creatinine. In FSGS, NAG excretion correlated with the following: blood urea nitrogen (BUN) (r = 0.8), serum protein (r = 0.57), serum cholesterol (r = 0.85), serum albumin (r = -0.68) and proteinuria (r = 0.56). In FSGS the gamma-GT excretion was not significantly different from MCNS in remission or in relapse. In FSGS, gamma-GT excretion correlated with the following: BUN (r = 0.48), serum creatinine (r = -0.66), serum protein (r = -0.54), serum albumin (r = -0.68) and serum cholesterol (r = 0.87). Compared with controls, the urinary excretion of 5 amino acids was increased in FSGS patients as a possible indicator of tubular damage. The value for 7 amino acids was reduced in MCNS patients. Urinary amino acid excretion was not different from controls for the other amino acids in either FSGS or MCNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of anion exchanger activity reduce sodium chloride-dependent taurine transport by brush border vesicles

The erythrocyte anion exchanger, or band 3 protein, catalyzes the exchange of chloride and bicarbonate in many cells. Anion exchanger activity is predominantly found in the basolateral membrane of the cortical collecting duct. Because proximal tubular renal taurine uptake across the brush border surface is dependent upon sodium and chloride, the effect of inhibitors of anion exchanger activity on renal taurine accumulation by rat renal brush border membrane vesicles was examined. The anion exchanger probes, DIDS (4,4-'diisothiosulfonic acid), and NBD-taurine (N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl]-aminoethane sulfonic acid), and NBD-taurine (N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl]-aminoethane sulfonic acid), were used as inhibitors of anion exchanger activity. DIDS, NAP-, and NBD-taurine all markedly inhibit the initial rate of NaCl-dependent accumulation of taurine by brush border membrane vesicles. NAP- and NBD-taurine accumulation is chloride dependent because inhibition was not found when uptake was performed in the presence of NaNO3 in place of chloride. In the presence of maximal inhibition of taurine uptake by NAP- or NBD-taurine, no additional inhibition was evident after incubation with DIDS. On the other hand, when a competitive inhibitor of taurine uptake, beta-alanine, was used, additional inhibition of taurine accumulation was found in the presence of NAP- or NBD-taurine (p < .01 respectively). These results suggest some interaction of the anion exchanger and the taurine accumulation process at the apical surface of the proximal tubule. Because NBD-taurine is a fluorescent probe, it may be possible to isolate membrane peptides that bind NBD-taurine and demonstrate fluorescence. Preliminary isoelectric focusing experiments of brush border protein incubated with NBD-taurine show fluorescence localized to several particular fractions. Hence this observation that inhibitors of the anion exchanger system block NaCl-dependent taurine uptake can potentially serve as a means of isolating the taurine transporter protein.

Gamma Glutamyl Transferase in domestic animals

In domestic animals, Gamma Glutamyl Transferase is mainly in the kidneys, the pancreas and the intestine; its liver activity is relatively high in cows, horses, sheep and goats and very low in dogs, cats and birds. The use of plasma reference values can help to interpret the variations of serum GGT mainly in hepatobiliary diseases of cattle, sheep, goats and cholestatic disorders of dogs. Urinary GGT is a good test of kidney toxic damage.

Evidence for a dipeptide transport system in renal brush border membranes from rabbit

Papain treatment of renal brush border vesicles was carried out as a successful first step towards the purification of the membrane components involved in dipeptide transport. The treated vesicles exhibited increased specific transport activity of glycyl-L-proline. In contrast, the specific transport activity of L-alanine in the treated vesicles was less than that in the control vesicles. Papain treatment resulted in the solubilization of 38% of protein, 55% of alkaline phosphatase, 90% of gamma-glutamyltransferase and 95% of leucine aminopeptidase. There was no change in the intravesicular volume nor was there any increase in vesicular permeability. Glycyl-L-proline transport was Na+-independent in the control and papain-treated vesicles. Diamide reduced the Na+-dependent L-alanine transport while glycyl-L-proline transport remained unaffected in the presence of Na+. Many dipeptides inhibited glycyl-L-proline transport both in the presence and absence of Na+. The inhibition by dipeptides was greater than the inhibition by equivalent concentrations of free amino acids. These data demonstrate that renal brush border vesicles can efficiently handle dipeptides by a mechanism completely different from that of amino acid transport.