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Y L Chan

Publications and source records attributed to Y L Chan.

At least 163 records · Page 9Linked to original sources
PubMed1989

Neural control of distal tubular bicarbonate and fluid transport.

Although previous studies have shown that inhibition of proximal tubular reabsorption of bicarbonate and fluid partially accounts for bicarbonaturia and diuresis observed in the denervated kidney, the role of the distal convoluted tubule in the neural regulation of electrolyte excretion has not been defined. This study was designed to examine the effects of denervation on bicarbonate and fluid reabsorption in the distal convoluted tubules by using in situ microperfusion methods. Early distal tubules were perfused with a solution containing 15 mM bicarbonate at a rate of 12 nl/min, and fluid samples were collected from the late distal tubule. Bicarbonate concentrations were measured as total CO2 by microcalorimetry. The rate of fluid absorption (Jv) was determined using [methoxy-3H]inulin as a volume marker. Before denervation, the rate of bicarbonate absorption (JHCO3-) was 24.7 +/- 2.6 peq.min-1.mm-1, and Jv was 1.80 +/- 0.14 nl.min-1.mm-1. After denervation, marked reductions in JHCO3- (51%) and Jv (60%) were observed. In contrast, sham denervation did not affect JHCO3- or Jv significantly. Our results indicate that the distal convoluted tubule can reabsorb bicarbonate and fluid under physiological conditions. We conclude that the transport processes in this segment of the nephron are regulated by renal nerve activity.

Absorption↗
PubMed1989

Renal bicarbonate reabsorption in the rat. III. Distal tubule perfusion study of load dependence and bicarbonate permeability.

Using continuous microperfusion techniques, we studied the load dependence of bicarbonate reabsorption along cortical distal tubules of the rat kidney and their bicarbonate permeability. Net bicarbonate transport was evaluated from changes in tracer inulin concentrations and total CO2 measurements by microcalorimetry. Bicarbonate permeability was estimated from the flux of total CO2 along known electrochemical gradients into bicarbonate-and chloride-free perfusion solution containing 10(-4) M acetazolamide. Transepithelial potential differences were measured with conventional glass microelectrodes. Significant net bicarbonate reabsorption occurred at luminal bicarbonate levels from 5 to 25 mM, and at perfusion rates from 5 to 30 nl/min. Bicarbonate reabsorption increased in a load-dependent manner, both during increments in luminal bicarbonate concentration or perfusion rate, reaching saturation at a load of 250 pmol/min with a maximal reabsorption rate of approximately 75 pmol/min.mm. Rate of bicarbonate reabsorption was flow dependent at luminal concentrations of 10 but not at 25 mM. During chronic metabolic alkalosis, maximal rates of reabsorption were significantly reduced to 33 pmol/min.mm. The bicarbonate permeability was 2.32 +/- 0.13 x 10(-5) cm/s in control rats, and 2.65 +/- 0.26 x 10(-5) cm/s in volume-expanded rats. Our data indicate that at physiological bicarbonate concentrations in the distal tubule passive bicarbonate fluxes account for only 16-21% of net fluxes. At high luminal bicarbonate concentrations, passive bicarbonate reabsorption contributes moderately to net reabsorption of this anion.

Absorption↗
PubMed1989

Effect of L-arginine on renal tubular bicarbonate reabsorption by the rat kidney.

This study was designed to characterize the effect of L-arginine, a dibasic amino acid, on bicarbonate reabsorption (RHCO3) by the superficial proximal convoluted tubule using the technique of microperfusion in situ and on overall kidney RHCO3 using clearance techniques. Luminal perfusion of proximal tubules with L-arginine (5, 10, and 20 mM) resulted in a concentration-dependent inhibition of RHCO3. Capillary perfusion with L-arginine (10 mM) had no significant effect indicating that this amino acid must gain access into the cell from the luminal side to inhibit RHCO3. The inhibitory effect of L-arginine on RHCO3 was stereospecific since luminal perfusion with D-arginine (10 mM) had no significant effect on RHCO3. The lowest concentration of luminal L-arginine (5 mM) which produced a significant inhibitory effect on RHCO3 (about 13% inhibition) was comparable to that measured in the blood of rats infused with this amino acid (6.4 +/- 0.7 mM). Systemic infusion of L-arginine resulted in metabolic acidosis and only a slight increase in HCO3 excretion. To investigate whether the lack of overt bicarbonaturia was due to the reduced filtered load of HCO3 or to a stimulatory effect of acidemia on distal HCO3 reabsorption, blood bicarbonate was elevated by the infusion of NaHCO3. Under those conditions overall kidney absolute RHCO3, examined as a function of filtered load, was maximal in rats infused with L-arginine, thereby suggesting that when proximal HCO3 transport is inhibited, RHCO3 beyond the end of the proximal convoluted tubule increases in a load-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1988

The cytotoxins alpha-sarcin and ricin retain their specificity when tested on a synthetic oligoribonucleotide (35-mer) that mimics a region of 28 S ribosomal ribonucleic acid.

An oligoribonucleotide (35-mer) that mimics the alpha-sarcin and the ricin region of eukaryotic 28 S rRNA was transcribed in vitro from a synthetic template with T7 RNA polymerase and was used to test whether the specificity of the hydrolysis by the toxins was retained. alpha-Sarcin, at a low concentration, cleaved a single phosphodiester bond on the 3' side of a guanosine residue in the synthetic oligomer that corresponds to G-4325 in 28 S rRNA, the site of action of the toxin in intact ribosomes. At a high concentration of alpha-sarcin, the substrate (35-mer) was hydrolyzed after each of its purines. alpha-Sarcin was without an effect on a synthetic RNA (20-mer) that reproduces the near universal sequence of nucleotides in the loop, but lacks the stem, of the toxin's domain. Thus, the specificity of the attack of alpha-sarcin on a precise region of 28 S rRNA appears to be contingent on the sequence of the nucleotides and the structure of the domain. Ricin depurinated a nucleotide in the synthetic oligomer (35-mer), and in the presence of aniline the phosphoribose backbone was cleaved at a position that conforms to A-4324 in 28 S rRNA, the site of action of the toxin in vivo.

Base Sequence↗
PubMed1988

The primary structure of rat ribosomal protein S6.

The amino acid sequence of rat ribosomal protein S6, the major phosphoprotein in the organelle, was deduced from the sequence of nucleotides in two recombinant cDNAs and confirmed from the sequence of amino acids in portions of the protein. Ribosomal protein S6 contains 249 amino acids and has a molecular weight of 28,683. The protein has 15 seryl residues; 7 are located in the carboxyl-terminal sequence of 15 amino acids and probably include most if not all of the residues that are phosphorylated. There are related repeated sequences of 10 amino acids each that occur at four separate positions in S6 and that are very basic. Rat S6 is homologous to Saccharomyces cerevisiae S10 (the extent of the identity is 75%) and most likely also to Schizosaccharomyces pombe S6.

Amino Acid Sequence↗
PubMed1988

The primary structure of rat ribosomal protein L18.

The amino acid sequence of rat ribosomal protein L18 was deduced from the sequence of nucleotides in a recombinant cDNA and confirmed from the amino-terminal amino acid sequence of the protein. Ribosomal protein L18 contains 187 amino acids (the amino-terminal methionine is removed after translation of the mRNA) and has a molecular weight of 21,530. Hybridization of the cDNA to digests of nuclear DNA suggests that there are 10-14 copies of the L18 gene. Rat ribosomal protein L18 is homologous to Xenopus laevis L14; the extent of the identity of the amino acid sequences is 87% and for the nucleotides in the coding region of the DNA it is 76%.

Amino Acid Sequence↗
PubMed1988

Primary structure of rat ribosomal protein L36a.

The amino acid sequence of rat ribosomal protein L36a, which may form part of the peptidyl transferase center, was deduced from the sequence of nucleotides in a recombinant cDNA and confirmed from the amino-terminal amino acid sequence of the protein. Ribosomal protein L36a contains 105 amino acids (the amino-terminal methionine is removed after translation of the mRNA) and has a molecular weight of 12,311. Hybridization of the cDNA to digests of nuclear DNA suggests that there are multiple copies of the L36a gene. Rat ribosomal protein L36a is homologous to a protein HL44 present in ribosomes of humans and protein 44 from Saccharomyces cerevisiae ribosomes.

Amino Acid Sequence↗
PubMed1988

Effect of amino acids on renal tubular bicarbonate reabsorption by the rat kidney.

This study shows that L-arginine, a dibasic amino acid, which decreases in proximal convoluted tubule HCO3 transport, does not inhibit renal Na+/K+ ATPase activity or O2 consumption in vitro. Thus, a mechanism(s) other than inhibition of Na+/K ATPase likely accounts for the inhibitory effect of dibasic aminoacids on HCO3 transport in the superficial proximal convoluted tubule. Neutral and acid aminoacids, unlike dibasic aminoacids, do not inhibit HCO3 transport in this nephron segment.

Absorption↗
PubMed1988

Angiotensin receptor mediated regulation of transport in the rat proximal tubule.

The intracellular mechanism of Ang II action, as supported by the present data, may be summarized by the following: Ang II interacts with its receptors, leading to an increase in cytosolic Ca+2 by mobilization of Ca+2 from intracellular pools. This rise in cytosolic Ca+2 initiates the activation of calmodulin-regulated enzymes. This then leads to inhibition of both JV and JHCO3-.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1987

The primary structure of rat ribosomal protein S8.

The amino acid sequence of rat ribosomal protein S8 was deduced from the sequence of nucleotides in a recombinant cDNA and confirmed from the NH2- and carboxyl-terminal amino acid sequences of the protein. Ribosomal protein S8 contains 207 amino acids (the NH2-terminal methionine is removed after translation of the mRNA) and has a molecular weight of 23,928. Hybridization of the cDNA to digests of nuclear DNA suggests that there are 7-9 copies of the S8 gene. Ribosomal protein S8 contains a possible internal repeat that has 12 or 13 residues, is basic, and occurs 5 times in the protein.

Amino Acid Sequence↗
PubMed1987

The primary structure of rat ribosomal protein S12. The relationship of rat S12 to other ribosomal proteins and a correlation of the amino acid sequences of rat and yeast ribosomal proteins.

The covalent structure of the rat 40 S ribosomal subunit protein S12 was determined from the sequence of amino acids in tryptic, chymotryptic, thermolytic, and cyanogen bromide peptides and inferred from the sequence of nucleotides in a recombinant cDNA. Rat ribosomal protein S12 contains 129 amino acids and has a molecular weight of 14,120. The amino acid sequences of a number of ribosomal proteins appear to be related to rat S12. These include spinach chloroplast L7, Escherichia coli S5, Nicotiana tabacum chloroplast S18, and Bacillus stearothermophilus S12, and perhaps others. In addition, there are two sequences, 26 and 18 amino acids in length, in rat S12 that may be related to segments of the same number of residues in ribosomal proteins from a number of species. These, and other results, reinforce the suggestion that ribosomal proteins form an extended family.

Amino Acid Sequence↗
PubMed1987

The primary structure of rat ribosomal protein L7. The presence near the amino terminus of L7 of five tandem repeats of a sequence of 12 amino acids.

The covalent structure of rat ribosomal protein L7 was determined in part from the sequence of nucleotides in a recombinant cDNA and in part from the sequence of amino acids in portions of the protein. The complementary analyses supplemented and confirmed each other. Ribosomal protein L7 contains 258 amino acids and has a molecular weight of 30,040. The protein has an unusual and striking structural feature near the NH2 terminus: five tandem repeats of a sequence of 12 residues. Rat L7 appears to be related to ribosomal protein L7 from the moderate halophile Vibrio costicola and perhaps to L30 from Bacillus stearothermophilus, to L7 from the moderate halophile NRCC 41227, and to L22 from Nicotinia tobaccum chloroplast. In addition, there is a sequence of 24 amino acids in rat protein L7 that may be related to segments of the same number of residues in Escherichia coli ribosomal proteins S10, S15, L9, and L22.

Amino Acid Sequence↗
PubMed1987

The primary structure of rat ribosomal protein L5. A comparison of the sequence of amino acids in the proteins that interact with 5 S rRNA.

The covalent structure of rat ribosomal protein L5, which associates with 5 S rRNA in the organelle, was deduced from the sequence of nucleotides in a recombinant cDNA (pL5-6-4) and confirmed from the sequences of amino acids in portions of the protein. Ribosomal protein L5, encoded by pL5-6-4, contains 296 amino acids and has a molecular weight of 34,298. However, a second recombinant cDNA, pL5-8-5, encodes a protein with an additional methionyl residue at position 236 and may be the product of a second active L5 gene. Rat L5 is homologous to yeast YL3 and to Halobacterium cutirubrum HL13, proteins that also bind to 5 S rRNA. No significant structural similarity, however, was found between rat L5 and other 5 S rRNA-binding proteins; not with a second H. cutirubrum protein HL19, nor the Escherichia coli ribosomal proteins, L5, L18, or L25, nor the Xenopus laevis transcription factor IIIA. H. cutirubrum HL19, however, has structural identity with E. coli L5 and seems to be related to yeast YL3 and, hence, may be an evolutionary link between the prokaryotic and eukaryotic 5 S rRNA-binding proteins. A group of ribosomal proteins not known to be associated with 5 S rRNA are also related to rat L5. They include: rat L39, Euglina gracilis chloroplast S7, Saccharomyces cerevisiae L31 and L46, Homo sapiens L32 and, perhaps, several others as well. There is an especially close interrelationship between rat L5, rat L39, yeast L46, human L32, and mouse L32. These results, and others, suggest that ribosomal proteins form an extended family and that L5 may contain in its structure traces of this affinity.

Amino Acid Sequence↗
PubMed1987

Effect of norepinephrine on renal tubular Na-K-ATPase and oxygen consumption.

Previous studies from this laboratory have demonstrated that norepinephrine (NE) increases sodium dependent phenylalanine uptake by in vitro rat cortical tubules. In the present study, we have examined whether the observed increase in proximal tubular sodium transport, during NE treatment, is related to changes in membrane Na-K-ATPase and cellular oxygen consumption. Treatment of intact tubules with NE increased microsomal Na-K-ATPase activity but had no effect on cellular oxygen consumption or ouabain inhibitable oxygen consumption. The increased Na-K-ATPase activity is consistent with the observed increase in sodium transport while the lack of a detectable effect on oxygen consumption suggests that the increased transport does not require additional oxygen utilization.

Animals↗
PubMed1987

The primary structure of rat ribosomal protein L19. A determination from the sequence of nucleotides in a cDNA and from the sequence of amino acids in the protein.

The covalent structure of rat ribosomal protein L19 was inferred from the sequence of nucleotides in a recombinant cDNA and confirmed from the sequence of amino acids in a portion of the protein. Ribosomal protein L19 contains 196 amino acids and has a molecular weight of 26,971. There are indications that a segment of 23 residues in rat L19 is related to sequences of the same length in Escherichia coli ribosomal proteins L30, L18, and S2.

Amino Acid Sequence↗
PubMed1986

Evidence for the presence of functional beta-adrenoceptor along the proximal tubule of the rat kidney.

Evidence for the presence of beta adrenoceptors on proximal tubules from the rat kidney has been obtained using enriched tubule suspensions prepared by Percoll centrifugation. Intact tubules demonstrated simultaneous enrichment of parathyroid hormone and isoproterenol sensitive cAMP production with no enrichment of antidiuretic hormone sensitive cAMP production. Both norepinephrine and epinephrine were less potent than isoproterenol and the stimulatory effect of catecholamines could be blocked with propranolol but not phentolamine. The stimulatory effect of norepinephrine on cellular phenylalanine uptake is blunted by co-addition of isoproterenol suggesting that the beta receptor may modulatory catecholamine stimulated transport.

Animals↗