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Biomedical subjects

B Malik

Publications and source records attributed to B Malik.

15 recordsLinked to original sources
PubMed2002

Mechanisms of aldosterone's action on epithelial Na + transport.

Aldosterone maintains total organism sodium balance in all higher vertebrates. The level of sodium reabsorption is primarily determined by the action of aldosterone on epithelial sodium channels (ENaC) in the distal nephron. Recent work shows that, in an aldosterone-sensitive renal cell line (A6), aldosterone regulates sodium reabsorption by short- and long-term processes. In the short term, aldosterone regulates sodium transport by inducing expression of the small G-protein, K-Ras2A, by stimulating the activity of methyl transferase and S-adenosyl-homocysteine hydrolase to activate Ras by methylation, and, possibly, by subsequent activation by K-Ras2A of phosphatidylinositol phosphate-5-kinase (PIP-5-K) and phosphatidylinositol-3-kinase (PI-3-K), which ultimately activates ENaC. In the long term, aldosterone regulates sodium transport by altering trafficking, assembly, and degradation of ENaC.

Aldosterone↗
PubMed2001

Enac degradation in A6 cells by the ubiquitin-proteosome proteolytic pathway.

Amiloride-sensitive epithelial Na(+) channels (ENaC) are responsible for trans-epithelial Na(+) transport in the kidney, lung, and colon. The channel consists of three subunits (alpha, beta, gamma) each containing a proline rich region (PPXY) in their carboxyl-terminal end. Mutations in this PPXY domain cause Liddle's syndrome, an autosomal dominant, salt-sensitive hypertension, by preventing the channel's interactions with the ubiquitin ligase Neural precursor cell-expressed developmentally down-regulated protein (Nedd4). It is postulated that this results in defective endocytosis and lysosomal degradation of ENaC leading to an increase in ENaC activity. To show the pathway that degrades ENaC in epithelial cells that express functioning ENaC channels, we used inhibitors of the proteosome and measured sodium channel activity. We found that the inhibitor, MG-132, increases amiloride-sensitive trans-epithelial current in Xenopus distal nephron A6 cells. There also is an increase of total cellular as well as membrane-associated ENaC subunit molecules by Western blotting. MG-132-treated cells also have increased channel density in patch clamp experiments. Inhibitors of lysosomal function did not reproduce these findings. Our results suggest that in native renal cells the proteosomal pathway is an important regulator of ENaC function.

Amino Acid Sequence↗
PubMed2000

Differential effects of protein kinase C on the levels of epithelial Na+ channel subunit proteins.

Regulation of epithelial Na(+) channel (ENaC) subunit levels by protein kinase C (PKC) was investigated in A6 cells. PKC activation altered ENaC subunit levels, differentially decreasing the levels of both beta and gamma, but not alphaENaC. Temporal regulation of beta and gammaENaC by PKC differed; gammaENaC decreased with a time constant of 3.7 +/- 1.0 h, whereas betaENaC decreased in 13.9 +/- 3. 0 h. Activation of PKC also resulted in a decrease in trans-epithelial Na(+) reabsorption for up to 48 h. PMA activation of PKC resulted in negative feedback inhibition of PKC protein levels beginning within 4 h. Both beta and gammaENaC levels, as well as transport tended toward pretreatment values after 48 h of PMA treatment. PKC inhibitors attenuated the effects of PMA on ENaC subunit levels and Na(+) transport. These results directly show for the first time that PKC differentially regulates ENaC subunit levels by decreasing the levels of beta and gamma but not alphaENaC protein. These results imply a PKC-dependent, long term decrease in Na(+) reabsorption.

Aldosterone↗
PubMed2000

Selection of peptidic mimics of digoxin from phage-displayed peptide libraries by anti-digoxin antibodies.

Since the initial report of the development of methodology to generate high-affinity digitalis-specific (digoxin) antibodies, these antibodies have proven extremely useful tools to monitor digoxin levels in digitalized patients and, as Fab fragments, to reverse toxic digoxin effects in life-threatening digoxin overdoses. These antibodies (both digoxin-specific and ouabain-specific) have been used extensively by investigators for the identification and characterization of putative endogenous digitalis-like factors. In this study, we used two well-characterized mouse anti-digoxin monoclonal antibodies (mAbs), designated 26-10 and 45-20, as binding templates with which to select short bacteriophage-displayed (pIII protein inserted) peptides that are capable of binding to these mAbs and mimicking the conformational structure of digoxin. Selective enrichment from two phage-displayed random peptide libraries enabled us to isolate and identify distinct 15 and 26 amino acid residue peptide inserts that bind with high avidity and idiotypic specificity to the selecting mAbs. Among these displayed inserts a subset was identified whose mAb binding is inhibited by digoxin and whose corresponding synthetic peptides inhibit phage binding. They, therefore, appear to bind at the mAbs digoxin-binding sites. These data provide the first clear evidence that short polypeptides can serve as surrogates for the low molecular mass hapten digoxin.

Amino Acid Sequence↗
PubMed2000

[Urinary trypsin inhibitor in pregnant women with normal and pathological course of pregnancy].

Urinary trypin inhibitor concentration (UTI) was measured by Fritz and all method in the groups of women: non-pregnant (I), pregnant (II), in pregnancy complicated by EPH-gestosis (III) and in the prolongated pregnancy (IV). Furthermore, in the urine from the investigated group the index protein/creatinine was established. There was noticed the statistically significant increase in the UTI concentration in II, III, IV groups comparing to the non-pregnant group--I, and the increase in UTI in III and IV group in comparison to group II. The UTI measurement in the pregnant women connected with the index protein/creatinine could be significant for diagnosing of the pathology of pregnancy.

Adolescent↗
PubMed2000

[Concentration of cysteine proteinase inhibitors in urine, amniotic fluid and serum from women in pregnancy complicated by EPH-gestosis].

Cysteine proteinase inhibitors (IPC) concentration was measured by the modified Barrett method using papaine in urine, amniotic fluid and serum obtained from the healthy labored women and from labored women in pregnancy complicated by EPH-gestosis. It was noticed the statistically significant increase in the IPC concentration in the material from the pregnant women with EPH-gestosis comparing to the women, which pregnancy had the physiologically normal course.

Adult↗
PubMed2000

Effect of titanium exposure on embryonic development during pre-implantation period in rats.

Doses of titanium trichloride (1/10th and 1/5th of LD50) were administered once and daily to pregnant rats to assess their effect on embryonic development. 1/5th dose of TiCl3 administered once orally on 1st, 2nd and 3rd day post-coitum. Similarly 1/10th of LD50 was administered daily. Results revealed that 1/10th LD50 dose of TiCl3 was more effective during pre-implantation period as number of 4 and 8-celled embryos decreased as compared to 1/5th. Delayed hatching of the blastocysts on day 5 was registered in TiCl3 treated dam.

Animals↗
PubMed1999

Antisense oligonucleotides against the alpha-subunit of ENaC decrease lung epithelial cation-channel activity.

Amiloride-sensitive Na+ transport by lung epithelia plays a critical role in maintaining alveolar Na+ and water balance. It has been generally assumed that Na+ transport is mediated by the amiloride-sensitive epithelial Na+ channel (ENaC) because molecular biology studies have confirmed the presence of ENaC subunits alpha, beta, and gamma in lung epithelia. However, the predominant Na+-transporting channel reported from electrophysiological studies by most laboratories is a nonselective, high-conductance channel that is very different from the highly selective, low-conductance ENaC reported in other tissues. In our laboratory, single-channel recordings from apical membrane patches from rat alveolar type II (ATII) cells in primary culture reveal a nonselective cation channel with a conductance of 20.6 +/- 1.1 pS and an Na+-to-K+ selectivity of 0.97 +/- 0.07. This channel is inhibited by submicromolar concentrations of amiloride. Thus there is some question about the relationship between the gene product observed with single-channel methods and the cloned ENaC subunits. We have employed antisense oligonucleotide methods to block the synthesis of individual ENaC subunit proteins (alpha, beta, and gamma) and determined the effect of a reduction in the subunit expression on the density of the nonselective cation channel observed in apical membrane patches on ATII cells. Treatment of ATII cells with antisense oligonucleotides inhibited the production of each subunit protein; however, single-channel recordings showed that only the antisense oligonucleotide targeting the alpha-subunit resulted in a significant decrease in the density of nonselective cation channels. Inhibition of the beta- and gamma-subunit proteins alone or together did not cause any changes in the observed channel density. There were no changes in open probability or other channel characteristics. These results support the hypothesis that the alpha-subunit of ENaC alone or in combination with some protein other than the beta- or gamma-subunit protein is the major component of lung alveolar epithelial cation channels.

Animals↗
PubMed1999

[Changes in arylsulphatase activity (EC 3.1.6.1) in the blood serum and urine in women during pregnancy and in the course of delivery].

By the determination of arylsulphatase A activity (EC 3.1.6.1) in the blood serum and urine obtained from 66 women using the modified method by Lee-Vaupel and Conzelmann it was noticed the increase in the enzyme activity during the pregnancy comparing to the non-pregnant group. The highest enzyme activity was observed in the III trimester of pregnancy. In the following stages of delivery (I, II, III) it was assumed the increase in enzyme activity in urine. The highest enzyme activity in urine was observed in the stage III, and in the serum--in the stage II. It was compared the enzyme activity in primiparae and multiparae proving, that in the serum nd urine this activity is higher in the stages I and II in multiparae, and in the stage III in primiparae.

Adult↗
PubMed1999

[Changes in arylsulphatase activity (EC 3.6.1) in the blood serum and urine in women during the pregnancy and in the course of delivery].

By the determination of arylsulphatase A activity (EC 3.1.6.1) in the blood serum and urine obtained from 66 women using the modified method by Lee-Vaupel and Conzelmann it was noticed the increase in the enzyme activity during the pregnancy comparing to the non-pregnant group. The highest enzyme activity was observed in the III trimester of pregnancy. In the following stages of delivery (I, II, III) it was assumed the increase in enzyme activity in urine. The highest enzyme activity in urine was observed in the stage III, and in the serum--in the stage II. It was compared the enzyme activity in primiparae and multiparae proving, that in the serum nd urine this activity is higher in the stages I and II in multiparae, and in the stage III in primiparae.

Adult↗
PubMed1993

Identification of the amino acids comprising a surface-exposed epitope within the nucleotide-binding domain of the Na+,K(+)-ATPase using a random peptide library.

Monoclonal antibodies that bind native protein can generate considerable information about structure/function relationships, but identification of their epitopes can be problematic. Previously, monoclonal antibody M8-P1-A3 has been shown to bind to the catalytic (alpha) subunit of the Na+,K(+)-ATPase holoenzyme and the synthetic peptide sequence 496-HLLVMK*GAPER-506, which includes Lys 501 (K*), the major site for fluorescein-5'-isothiocyanate labeling of the Na+,K(+)-ATPase. This sequence region of alpha is proposed to comprise a portion of the enzyme's ATP binding domain (Taylor, W. R. & Green, N. W., 1989, Eur. J. Biochem. 179, 241-248). In this study we have determined M8-P1-A3's ability to recognize the alpha-subunit or homologous E1E2-ATPase proteins from different species and tissues in order to deduce the antibody's epitope. In addition the bacteriophage random peptide or "epitope" library, recently developed by Scott and Smith (1990, Science 249, 386-390) and Devlin et al. (Devlin, J. J., Panganiban, L. C., & Devlin, P. E., 1990, Science 249, 404-406), has served as a convenient technique to confirm the species-specificity mapping data and to determine the exact amino acid requirements for antibody binding. The M8-P1-A3 epitope was found to consist of the five amino acid 494-PRHLL-498 sequence stretch of alpha, with residues PRxLx being critical for antibody recognition.

Adenosine Triphosphate↗
PubMed1985

Does antacid prophylaxis prevent upper gastrointestinal bleeding in critically ill patients?

Sixty-five surgical ICU patients at high risk of developing acute erosive gastritis and bleeding received prophylactic antacid treatment to maintain a gastric pH of at least 5.0. A similar control group of 61 patients received no specific prophylaxis. All patients in both groups developed microscopic bleeding; however, microscopic bleeding did not influence outcome. In the control group, eight (13.1%) patients developed moderate visible bleeding, as compared to seven (10.8%) patients in the antacid group, an insignificant difference. A single patient in the control group developed severe GI bleeding due to acute erosive gastritis. Antacid prophylaxis did not prevent macroscopic bleeding and there was no correlation between the number of risk factors in individual patients and the rate of upper GI bleeding. We conclude that antacid is not required to prevent upper GI bleeding in high-risk critically ill patients.

Adolescent↗