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Biomedical subjects

L C Garg

Publications and source records attributed to L C Garg.

At least 73 records · Page 4Linked to original sources
PubMed1986

Activities of cathepsins B and L in isolated nephron segments from proteinuric and nonproteinuric rats.

The intralysosomal proteinases cathepsins B and L were measured in microdissected segments of rat nephron. Z-Arg-Arg-NMec served as the substrate for cathepsin B and Z-Phe-Arg-NMec for cathepsin B and L together. Individual S1, S2, and S3 segments of proximal tubules, TDL, MTAL, CTAL, DCT, CCD, and OMCD were dissected from young female rats weighing 130 +/- 11 g with low protein excretion (0.68 +/- 0.1 mg/24 h), from older female rats weighing 289 +/- 9 g with protein excretion of 10 +/- 6.3 mg/24 h, from older male rats weighing 404 +/- 11 g with protein excretion of 22 +/- 6 mg/24 h, from female rats weighing 198 +/- 10 g with albumin-induced proteinuria (411 +/- 134 mg/24 h), and from female rats weighing 203 +/- 11 g with low protein excretion (2.7 +/- 0.4 mg/24 h). The distributions of cathepsin activities along the nephron were similar. In all five groups, S1 and S2 segments had enzyme activities three times higher than in all remaining segments. In S2 and S3, enzyme activities were two to three times higher in proteinuric animals. These findings suggest that in proteinuric animals the increase in the protein load delivered to the proximal tubules selectively stimulated cathepsin activities in the S2 and S3 segments, presumably because of an increase in protein uptake, and that cathepsins B and L participate in lysosomal digestion of protein reabsorbed from the glomerular filtrate via endocytosis.

Aging↗
PubMed1986

Hyperoxia reduces plasma membrane fluidity: a mechanism for endothelial cell dysfunction.

To evaluate the relative contributions of three possible mechanisms that can be advanced to explain the observation that hyperoxia decreases serotonin uptake by endothelial cells, we examined the effect of high O2 tensions on Na+-K+-ATPase activity, ATP content, and plasma membrane fluidity in cultured endothelial cells. Confluent monolayers of pulmonary artery and aortic endothelial cells were exposed to 95% O2 (hyperoxia) or 20% O2 (controls) in 5% CO2 at 1 ATA for 4-42 h. Exposure to high O2 tensions had no effect on Na+-K+-ATPase activity or ATP content in pulmonary artery or aortic endothelial cells in culture. However, hyperoxia decreased the fluidity of the plasma membrane of pulmonary artery and aortic endothelial cells in culture, and the time course for the decrease in fluidity parallels that of the hyperoxic inhibition of serotonin transport. These results indicate that hyperoxia decreases fluidity in the hydrophobic core of the plasma membranes of cultured endothelial cells. Such decreases in plasma membrane fluidity may be responsible for hyperoxia-induced alterations in membrane function including decreases in transmembrane transport of amines.

Adenosine Triphosphate↗
PubMed1985

Stimulation of an N-ethylmaleimide-sensitive ATPase in the collecting duct segments of the rat nephron by metabolic acidosis.

A plasma membrane ATPase sensitive to inhibition by N-ethylmaleimide (NEM) and insensitive to inhibition by oligomycin and ouabain has been shown to be involved in acidification of urine in the turtle bladder. The activity of this NEM-sensitive ATPase was determined in four types of distal nephron segments of normal rats and in rats treated with ammonium chloride. The enzyme activity was determined by a fluorometric micromethod in which ATP hydrolysis was coupled to NADH oxidation. Significant activities (10-35 pmol ADP X min-1 X mm-1) of NEM-sensitive ATPase were present in the distal convoluted tubule (DCT) and in the cortical and outer and inner medullary collecting duct segments of normal rats. In metabolic acidosis produced by ammonium chloride treatment (plasma CO2 content = 15.3 +/- 0.8 mequiv./L), the NEM-sensitive ATPase activity was increased significantly (60-100%) in the collecting duct segments without showing a significant change in the enzyme activity in the DCT. Our data are consistent with the hypothesis that a plasma membrane H+-ATPase (inhibited by NEM but not by oligomycin or ouabain) is involved in H+ secretion in the mammalian collecting duct.

Acidosis↗
PubMed1985

Glucocorticoid effects on Na-K-ATPase in rabbit nephron segments.

We determined the effect of dexamethasone on Na-K-ATPase activity in six nephron segments of the adrenalectomized rabbit. Treatment consisted of 1.4 micrograms dexamethasone X 100 g body wt-1 X day-1 for 7 days prior to the study of the nephron segments. Enzyme activity was determined in individual nephron segments by a microfluorometric assay. There was 40-50% less activity of Na-K-ATPase in the S1 portion of the proximal convoluted tubule (PCT, S1), the medullary thick ascending limb (MTAL), and the distal convoluted tubule (DCT) of adrenalectomized rabbits compared with that of control (sham-operated) animals. There was no significant difference in the enzyme activity in proximal straight tubules (PST, S2 and S3) and cortical thick ascending limb (CTAL) of adrenalectomized and control animals. Dexamethasone treatment produced a dexamethasone concentration of 5 +/- 0.8 nM in the plasma and increased Na-K-ATPase activity in PCT (S1), MTAL, and DCT of the adrenalectomized animals to the control levels without significantly affecting the enzyme activity in the PST (S2, S3) or CTAL. The concentration of dexamethasone in the plasma was such that the hormone should bind mainly to dexamethasone receptors (Kd = 5 nM) and very little to aldosterone receptors (Kd greater than 60 nM). Thus, glucocorticoids probably stimulate Na-K-ATPase in PCT, MTAL, and DCT through glucocorticoid (Type II) receptors and not through mineralocorticoid (Type I) receptors.

Adenosine Triphosphatases↗
PubMed1985

Na-K-ATPase in nephron segments of rats developing spontaneous hypertension.

Na-K-ATPase activity was determined in seven specific nephron segments of 5- and 12-wk-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) controls. The enzyme activity in proximal convoluted tubule (PCT) and proximal straight tubule (PST) was significantly higher in 5-wk-old SHR than in WKY. However, Na-K-ATPase activity in medullary thick ascending limb (MTAL), cortical thick ascending limb (CTAL), and distal convoluted tubule (DCT) was significantly lower in 5-wk-old SHR than in WKY. There were no significant differences in the enzyme activity in PCT, PST, MTAL, CTAL, and DCT in 12-wk-old SHR and WKY. Furthermore, there were no significant differences in Na-K-ATPase activity in collecting duct segments of 5- or 12-wk-old SHR and age-matched WKY. The possible role of the abnormal pattern of Na-K-ATPase activity in PCT, PST, MTAL, CTAL, and DCT in 5-wk-old SHR in generation of hypertension in this strain remains to be determined.

Age Factors↗
PubMed1985

Renal adaptation to potassium in the adrenalectomized rabbit. Role of distal tubular sodium-potassium adenosine triphosphatase.

Potassium secretion and sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity in the distal nephron segments are known to be influenced by the dietary intake of K+. This has been attributed to a change in the plasma aldosterone level, which also influences K+ secretion and Na-K-ATPase activity in the distal nephron. To investigate whether or not dietary K+ can modulate Na-K-ATPase activity in the distal nephron independently of aldosterone, we determined Na-K-ATPase activity in four distinct nephron segments of adrenalectomized (adx) rabbits given four specific diets for 1 wk before experimentation. Na-K-ATPase activity was determined by a fluorometric microassay in which ATP hydrolysis is coupled to NADH oxidation. The nephron segments examined were the distal convoluted tubule (DCT), the connecting tubule (CNT), the cortical collecting duct (CCD), and the outer medullary collecting duct (MCD). All diets were similar in composition except for their K+ contents, which were 100, 300, 500, and 700 meq/kg in groups 1-4, respectively. In these adx animals, Na-K-ATPase activity increased greater than 200% in the CCD as the dietary intake of K+ increased. There was a linear relationship between K+ excretion and the enzyme activity in this segment. There was a 50% increase in Na-K-ATPase activity in the CNT as the dietary intake of K+ increased in adx animals. However, there were no significant differences in Na-K-ATPase activities in the DCT and MCD among the four treatment groups. It is concluded that dietary K+ intake can influence Na-K-ATPase activity in the CCD and CNT independently of plasma aldosterone levels.

Adaptation, Physiological↗
PubMed1985

Sodium-potassium-adenosine triphosphatase in nephron segments of spontaneously hypertensive rats.

Sodium pump activity of blood vessels has been reported to decrease in several animal models of hypertension. We studied sodium-potassium-adenosine triphosphatase (Na-K-ATPase) activity of renal tubular segments in 12-week-old spontaneously hypertensive rats and in age-matched Wistar-Kyoto normotensive rats. The enzyme activity of the individual nephron segments was determined by a microfluorometric assay in which ATP hydrolysis is coupled with NADH oxidation. In the spontaneously hypertensive rats, systolic blood pressure was significantly higher (181 +/- 3 mm Hg) than in the Wistar-Kyoto rats (134 +/- 2 mm Hg). However, there was no difference in mean Na-K-ATPase activity in any of the nephron segments from the spontaneously hypertensive compared with the Wistar-Kyoto group. It is concluded that Na-K-ATPase activity does not change in any of the nephron segments with spontaneous hypertension.

Adenosine Triphosphatases↗
PubMed1985

Effects of thyroid hormone on Na-K-adenosine triphosphatase activity along the rat nephron.

Na-K-adenosine triphosphatase (ATPase) activity was determined in individual nephron segments obtained from the kidneys of euthyroid and hypothyroid rats. One group of animals was made hypothyroid by feeding 0.05% aminotriazole (ATZ) in the diet for 2 weeks. A second group received the same amount of ATZ plus 500 micrograms/kg body weight of L-thyroxine (T4) given subcutaneously each day for 2 weeks. A third group received the same diet without ATZ or T4. There was a 57% (P less than 0.01) decrease in Na-K-ATPase activity in the proximal convoluted tubule (PCT) in ATZ-treated rats that was corrected by the simultaneous administration of T4 with ATZ. A smaller (15% to 25%) and statistically nonsignificant decrease in Na-K-ATPase activity was observed in the cortical portion of the proximal straight tubule and in both the cortical and the medullary portions of the thick ascending limb in ATZ-treated rats. These changes in the enzyme activity were also corrected by simultaneous administration of T4 with ATZ. The results suggest that under the conditions of these experiments the PCT is a major site of action of thyroid hormone in the rat kidney.

Amitrole↗
PubMed1984

Acid phosphatase activity in the mammalian nephron.

Lysosomal acid phosphatase (AcPase) activity was measured in individual segments of rat and rabbit nephrons employing 4-methylumbelliferyl phosphate as the substrate. Generation of reaction product was linear with incubation time up to 127 min and with tubule length. Activity was much higher in glomeruli and proximal tubules of rat than rabbit kidney. In both rat and rabbit there were higher activities in juxtamedullary than in superficial glomeruli. In rats, AcPase activity decreased from S1 to S3 segments, which parallels the known decrease in the number of lysosomes. Surprisingly, in rabbits of both sexes AcPase activity in the cortical collecting duct (CCD), which contains a limited number of lysosomes, was comparable to levels measured in the S1 and S2 segments of the proximal tubule. Similarly, in the male rat values for AcPase activity in the cortical thick ascending limb, distal convoluted tubule, CCD, and medullary collecting duct paralleled those in the S3 segment. These findings suggest that a considerable amount of AcPase in the distal nephron is either extralysosomal or that the amount of lysosomal AcPase activity per unit volume is greater in distal nephron segments compared with the proximal tubule. Different K'm values for AcPase in S1 segments and CCD were found in the rabbit, suggesting the presence of different isoenzymes.

Acid Phosphatase↗
PubMed1983

Surface membrane-associated phosphatidylethanolamine N-methyltransferase activity in L-929 cells.

L-929 cell surface membranes were incubated with S-adenosyl-L-[methyl-3H]-methionine and found to contain phosphatidylethanolamine: S-adenosylmethionine N-methyltransferase (phosphatidylethanolamine N-methyltransferase) activity. The enzyme or combination of enzymes responsible for this activity methylated endogenous phosphatidylethanolamine and its methylated derivatives to yield phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine. Maximum enzyme activity was expressed at pH 6.9, the reaction was not dependent on the presence of divalent cations, and exogenously added phospholipids did not stimulate the rate of reaction. Phospholipid methylation was inhibited by S-adenosyl-L-homocysteine and by local anaesthetic drugs such as chlorpromazine and tetracaine which partition into the lipid bilayer. Control experiments demonstrated that the surface membrane-associated methyltransferase activity was not due to contamination of surface membrane preparations with intracellular membranes. Surface membranes were found to have higher specific methyltransferase activities than whole L-cell homogenates or endoplasmic reticulum-enriched microsomes. The low rate of methyltransferase function expressed in vitro (approximately 1 pmol/min . mg protein) suggests that phospholipid methylation is not a major metabolic source of surface membrane phosphatidylcholine.

Animals↗
PubMed1983

Friend erythroleukemia cell differentiation: induction by retinoids.

Growth in the presence of retinoids was found to induce erythroid differentiation in Friend murine erythroleukemia (MEL) cells in culture. The program of differentiated functions expressed by retinoid-treated cells was quite similar to that promoted by other inducers of MEL cell differentiation. For example, 70% or more of induced cells synthesized hemoglobin which accumulated to a level of 8 micrograms-10 micrograms per 10(6) cells. The level of acetylcholinesterase activity increased two to five-fold in induced cells, and induction by retinoids, like induction by dimethylsulfoxide (DMSO), promoted the appearance of cell surface lumps or 'blebs'. All-trans retinaldehyde, which promoted maximum hemoglobin and acetylcholinesterase synthesis at a concentration of 5 X 10(-7) M, was found to be a more potent inducer than all-trans retinoic acid or retinol, which both showed maximum induction at 1 X 10(-5) M. Like differentiation promoted by DMSO, retinoid-induced differentiation was inhibited by 10(-7) M dexamethasone.

Acetylcholinesterase↗
PubMed1983

Glyoxalase I in regenerating mouse liver exposed to carcinogens.

Glyoxalase I is the first component of glyoxalase system which is involved in detoxification of alpha-ketoaldehydes and converts them to nontoxic substances. This study reports changes in Glyoxalase I activity in relation to DNA synthesis in regenerating liver treated with two polycyclic aromatic hydrocarbons - 7,12-dimethylbenz (a) anthracene and benzo(a)pyrene. Livers after partial hepatectomy show consistent increase in Gly. I which reaches to its peak at 24 hr after surgery. [3H]Thymidine incorporation into DNA also follows the same trend as does Gly. I in regenerating liver. Both the carcinogens have significantly reduced the activity of Gly. I and DNA biosynthesis when compared with untreated partially hepatectomized control livers. The study reveals that though regenerating liver has been considered as an experimental model for neoplasia, unlike tumors (where Gly. I is either absent or in undetectable quantities) it possesses more Gly. I than in normal liver. On the other hand, preneoplastic liver during initiation (in regenerating liver treated with carcinogens, initiation is expected to occur) has very low activity. This suggests that Gly. I is not only involved in controlling growth but possibly is involved in some other phenomenon which is somehow depressed in preneoplastic and cancerous tissues.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1982

Effect of low potassium-diet on Na-K-ATPase in rat nephron segments.

Na-K-ATPase activity was determined in 10 segments of the rat nephron using a fluorometric microassay method [4]. The enzyme activity showed three peaks (greater than 200 pmol ADP min-1 mm-1) along the nephron of normal rats. These peaks were in the S1 portion of the proximal tubule, the medullary thick ascending limb from the inner stripe and the distal convoluted tubule. Feeding the rats a low potassium diet for 8 weeks produced a significant decrease in Na-K-ATPase activity in the cortical collecting duct, but no significant change in this enzyme in any other segment. The low potassium diet did not produce a significant change in Mg-ATPase in any nephron segments. We conclude that Na-K-ATPase activity along the rat nephron shows a pattern that is qualitatively similar to that seen in the rabbit nephron [4]. However, quantitatively the Na-K-ATPase activity in the rat nephron is greater than in the corresponding segments of the rabbit nephron. The results are consistent with the greater rate of glomerular filtration and Na+ reabsorption per rat nephron. Furthermore, our results suggest that the decrease in potassium excretion during potassium deficiency is modulated, at least in part, by the level of Na-K-ATPase activity in the cortical collecting duct.

Absorption↗
PubMed1981

Mineralocorticoid effects on Na-K-ATPase in individual nephron segments.

A fluorometric micromethod for the assay of Na-K-ATPase was used to determine Na-K-ATPase activity in 11 segments of the rabbit nephron. The Na-K-ATPase activity was found to be highest (greater than 100 pmol.mm1-.min-1) in proximal convoluted tubules (S1), medullary thick ascending limbs, distal convoluted tubules, and connecting tubules. There was a good correlation (r = 0.94) between Na-K-ATPase activity in different segments and net Na transport previously measured by in vitro tubule perfusion. Treatment of rabbits with deoxycorticosterone (DOCA) for 8-11 days produced increases in Na-K-ATPase activity of 100 and 500% in connecting tubules and cortical collecting ducts, respectively, without significant change in other segments. Maintenance on a low sodium diet for 12-18 days was associated with a 200% increase in Na-K-ATPase activity in cortical collecting ducts only. We conclude that the Na-K-ATPase activity is stimulated by mineralocorticoids in the cortical collecting duct in association with the previously observed changes in sodium transport.

Aldosterone↗
PubMed1980

Ocular hypotensive effects of timolol in cat eyes.

The effects of timolol on the aqueous humor (AH) formation and AH outflow in cat eyes were simultaneously studied with a continuous infusion method under constant intraocular pressure. The rate of AH formation was reduced 28%, 56%, and 71%, respectively, by 0.005%, 0.025%, and 0.15% of timolol solution infused intracamerally. There was no significant change of AH outflow after the administration of timolol. It was noted that the pupil was dilated by 0.025% and 0.15% timolol solutions. To determine the action mechanism of timolol to inhibit AH formation, experiments of carbonate dehydratase inhibition were performed with various concentrations of timolol. No appreciable enzyme inhibition was noted with timolol at concentrations up to 0.5%. It is thus concluded that the action mechanism of timolol to inhibit AH formation differs from that of carbonate dehydratase inhibitors.

Animals↗
PubMed1979

Evidence of a high-activity C type of carbonic anhydrase in human ciliary processes.

Carbonic anhydrase activity was found in the ciliary process of fresh human donor eyes, originating from an enzyme antigenically similar to the erythrocyte high-activity isoenzyme HCA C. It was sensitive to inhibition by acetazolamide and resistant to inhibition by halides like HCA C. The enzyme is probably identical with HCA C. Its tissue concentration was one fifth to one tenth of that in the human kidney. The erythrocyte low-activity isoenzyme HCA B was also found in the processes as a contaminant.

Acetazolamide↗