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Biomedical subjects

G Das

Publications and source records attributed to G Das.

At least 91 records · Page 5Linked to original sources
PubMed1989

Therapeutic review. Cardiac effects of atropine in man: an update.

The use of atropine in cardiovascular disorders is mainly in the management of patients with bradycardia. Atropine increases the heart rate and improves the atrioventricular conduction by blocking the parasympathetic influences on the heart. Recent observations that atropine in low doses results in paradoxical effects at the sinoatrial node (vagotonic) and the atrioventricular node (vagolytic) have lead to a concern for its safety in patients with acute myocardial infarction and bradycardia. This review discusses the basic cardiovascular pharmacology of the atropine, explores the mechanisms responsible for its paradoxical effects and discusses the clinical implications of these observations.

Atropine↗
PubMed1989

Beta-methyl digoxin: a better absorbable digoxin.

Since Megges and Repke [1961] showed that acetylation of the hydroxyl groups in the aglycone or the sugar side chain of the digitalis molecule results in a derivative with enhanced and more complete absorption from the gastrointestinal tract, several new compounds resulting from acetylation or methylation of digoxin molecule have been developed. Beta-methyl digoxin (beta-methyl digoxin) is a methyl derivative (methyl group in position 4 of the digitoxose residue) of digoxin. Enhanced and more complete gastrointestinal absorption of tritium labeled beta-methyl digoxin [Rennekamp et al. 1972] has been confirmed. Weiss et al. [1975], based on the serum levels following oral administration, calculated that to achieve comparable levels, digoxin dose would have to be increased by 1.55 times compared to that of beta-methyl digoxin. These and other studies supported an earlier notion that beta-methyl digoxin was a better and desirable cardiotropic agent than the digoxin. Comparison of cardiac effects using equivalent doses of the two compounds however, showed no difference [Das et al. 1977]. Following oral administration, the serum glycoside levels to beta-methyl digoxin indeed were significantly greater than those with digoxin. However, these differences in serum levels were not of sufficient magnitude to influence detectable cardiac inotropic effects, hence, the search for a better digoxin should continue.

Digoxin↗
PubMed1989

Fish oil in heart disease.

Observations of significantly lower total cholesterol, low density lipoprotein (LDL) cholesterol and higher levels of high density lipoprotein (HDL) cholesterol among Eskimos as compared to Danes in all age groups and both genders, and the current emphasis on the role of cholesterol in atherosclerosis have stimulated several studies that have examined the effects of dietary fish or fish oil supplements on plasma lipids. Conclusions from these studies suggest a favorable change in the plasma lipids in subjects with higher intake of dietary fish or those receiving fish oil supplements towards a decreased incidence of atherosclerosis and hence the coronary artery disease. This article is an attempt to review the current understanding of the effects of fish oil on blood lipids and its role in the heart disease.

Animals↗
PubMed1988

Replacements of lysine 32 in yeast cytochrome c. Effects on the binding and reactivity with physiological partners.

Lysine 32 has been previously implicated by chemical modification and modeling studies as a key component of the domain which controls recognition and binding of cytochrome c to its physiological partners, e.g. cytochrome b2, cytochrome c peroxidase, and cytochrome oxidase. In order to quantitate the importance of this residue, we have investigated the role of Lys-32 in the reactivity of cytochrome c in redox reactions in vitro and in vivo with protein partners by using a series of altered forms of iso-1-cytochrome c from the yeast Saccharomyces cerevisiae in which Lys-32 is replaced by Leu-32, Gln-32, Trp-32, and Tyr-32. Leu-32 and Gln-32 represent substitutions which change charge without seriously affecting the steric bulk of the side chain or the stability of the protein. For the Leu-32- and Gln-32-altered proteins, steady state kinetic studies with cytochrome c peroxidase, cytochrome b2, and cytochrome oxidase showed that neither of the steady state kinetic parameters, Km nor Vmax, were substantially modified by mutation. Studies of single turnover kinetics with a small molecule (ascorbate) or within bound complexes with either cytochrome b5 or cytochrome c peroxidase demonstrated that redox kinetics are only slightly affected by these substitutions. NMR experiments demonstrated that the Gln-32-altered protein can still bind strongly to a physiological partner, cytochrome c peroxidase. Growth in lactate medium demonstrated that the activity in vivo compared with the normal value was reduced to only 85% with the Gln-32- and Leu-32-altered proteins and to 65% with the Trp-32- and Tyr-32-altered proteins. These findings suggest that the evolutionary invariance of Lys-32 reflects only small quantitative changes in the binding and reactivity of cytochrome c.

Alleles↗
PubMed1988

Effects of amino acid replacements in yeast iso-1 cytochrome c on heme accessibility and intracomplex electron transfer in complexes with cytochrome c peroxidase.

The kinetics of reduction of wild type and several site-specific mutants of yeast iso-1 cytochrome c (Arg-13----Ile, Gln-16----Ser, Gln-16----Lys, Lys-27----Gln, Lys-72----Asp), both free and in 1:1 complexes with yeast cytochrome c peroxidase, by free flavin semiquinones have been studied. Intramolecular one-electron transfer from the ferrous cytochromes c to the H2O2-oxidized peroxidase at both low (8 mM) and high (275 mM) ionic strengths was also studied. The accessibility of the cytochrome c heme within the electrostatically stabilized complex and the rate constants for intramolecular electron transfer at both low and high ionic strength are highly dependent on the specific amino acids present at the protein-protein interface. Importantly, replacement by uncharged amino acids of Arg or Lys residues thought to be important in orientation and/or stabilization of the electron-transfer complex resulted in increased rates of electron transfer. In all cases, an increase in ionic strengths from 8 to 275 mM also produced increased intramolecular electron-transfer rate constants. The results suggest that the electrostatically stabilized 1:1 complex is not optimized for electron transfer and that by neutralization of key positively charged residues, or by an increase in the ionic strength thereby masking the ionic interactions, the two proteins can orient themselves to allow the formation of a more efficient electron-transfer complex.

Amino Acids↗
PubMed1988

Yeast iso-1-cytochrome c: genetic analysis of structural requirements.

We describe the use of classical and molecular genetic techniques to investigate the folding, stability, and enzymatic requirements of iso-1-cytochrome c from the yeast Saccharomyces cerevisiae. Interpretation of the defects associated with an extensive series of altered forms of iso-1-cytochrome c was facilitated by the recently resolved three dimensional structure of iso-1-cytochrome c [(1987) J. Mol. Biol. 199, 295-314], and by comparison with the phylogenetic series of eukaryotic cytochromes c. Residue replacements that abolish iso-1-cytochrome c function appear to do so by affecting either heme attachment or protein stability; no replacements that abolish electron transfer function without affecting protein structure were uncovered. Most nonfunctional forms retained at least partial covalent attachment to the heme moiety; heme attachment was abolished only by replacements of Cys19 and Cys22, which are required for thioether linkage, and His23, a heme ligand. Replacements were uncovered that retain function at varying levels, including replacements at evolutionarily conserved positions, some of which were structurally and functionally indistinguishable from wild type iso-1-cytochrome c.

Amino Acid Sequence↗
PubMed1988

Upstream regulatory elements are necessary and sufficient for transcription of a U6 RNA gene by RNA polymerase III.

Whereas the genes coding for trimethyl guanosine-capped snRNAs are transcribed by RNA polymerase II, the U6 RNA genes are transcribed by RNA polymerase III. In this study, we have analyzed the cis-regulatory elements involved in the transcription of a mouse U6 snRNA gene in vitro and in frog oocytes. Transcriptional analysis of mutant U6 gene constructs showed that, unlike most known cases of polymerase III transcription, intragenic sequences except the initiation nucleotide are dispensable for efficient and accurate transcription of U6 gene in vitro. Transcription of 5' deletion mutants in vitro and in frog oocytes showed that the upstream region, within 79 bp from the initiation nucleotide, contains elements necessary for U6 gene transcription. Transcription studies were carried out in frog oocytes with U6 genes containing 5' distal sequence; these studies revealed that the distal element acts as an orientation-dependent enhancer when present upstream to the gene, while it is orientation-independent but distance-dependent enhancer when placed down-stream to the U6 gene. Analysis of 3' deletion mutants showed that the transcription termination of U6 RNA is dependent on a T cluster present on the 3' end of the gene, thus providing further support to other lines of evidence that U6 genes are transcribed by RNA polymerase III. These observations suggest the involvement of a composite of components of RNA polymerase II and III transcription machineries in the transcription of U6 genes by RNA polymerase III.

Animals↗
PubMed1988

Efficacy of esmolol in the treatment and transfer of patients with supraventricular tachyarrhythmias to alternate oral antiarrhythmic agents.

The efficacy and safety of esmolol, a titratable intravenous beta-adrenergic blocking agent with a short elimination half-life (t 1/2 = 9.0 min) was evaluated in a multicenter open-label study for the treatment of supraventricular tachyarrhythmias (heart rate greater than 100 bpm). The study also investigated the feasibility of transferring patients from esmolol to alternate oral antiarrhythmic agents without loss of therapeutic response. Of the 113 patients studied, 95 (84%) achieved therapeutic response (reduction in heart rate of 15% or more or conversion to sinus rhythm). Most of these patients (93%) achieved the therapeutic response at esmolol doses of 200 micrograms/kg/min or lower. Transfer from esmolol to an oral antiarrhythmic agent(s) was studied in 76 patients. Alternate antiarrhythmic agents used in this study were digoxin (N = 25), propranolol (N = 21), verapamil (N = 10), metoprolol (N = 11), quinidine (N = 2), and a combination of two antiarrhythmic agents (N = 7). Sixty-seven (88%) patients were successfully transferred to oral antiarrhythmic agents without loss of the therapeutic response obtained with esmolol. The most frequent adverse effect observed during the study was hypotension, which resolved quickly (16 +/- 14 min) either by decreasing the dose or by discontinuation of esmolol infusion. This study supports previous observations concerning the safety and efficacy of esmolol in the treatment of supraventricular tachyarrhythmias. Furthermore, it demonstrates that the majority of patients successfully treated with esmolol can be safely and effectively transferred to oral therapy with alternate antiarrhythmic agents.

Adrenergic beta-Antagonists↗
PubMed1988

A highly revertible cyc1 mutant of yeast contains a small tandem duplication.

A mutant, cyc1-96, that reverts spontaneously at an extremely high rate, was uncovered after examining approximately 500 cyc1 mutants which lack or have defective iso-1-cytochrome c in the yeast Saccharomyces cerevisiae. Cloning and DNA sequencing of appropriate fragments revealed that the cyc1-96 mutation contained a 19 bp duplication whereas the spontaneously arising revertants contained the normal wild-type sequence. Because the 19 bp segment in the wild-type sequence is flanked by a 5 bp repeat and because the cyc1-96 mutation arose spontaneously, the 19 bp duplication may have arisen by slippage and misalignment during DNA synthesis. The high reversion rate was not diminished in strains containing the rad52 mutation, which generally reduces mitotic recombination, including recombination associated with the elimination of a segment of a long direct repeat. Thus the loss of segments from short and long duplications occur by different mechanisms. We suggest that the high reversion rates of cyc1-96 and other short duplications are due to misalignment errors during replication.

Amino Acid Sequence↗
PubMed1988

The ubiquitous octamer-binding protein Oct-1 contains a POU domain with a homeo box subdomain.

The octamer motif ATGCAAAT is recognized indistinguishably by two mammalian transcription factors: one that is expressed ubiquitously and referred to here as Oct-1, and another, Oct-2, that is expressed in lymphoid cells. We report the cDNA cloning of the human oct-1 gene, which encodes Oct-1, by screening lambda gt11 recombinant phage in situ for octamer motif-specific DNA binding. One lambda gt11 recombinant expressed a beta-galactosidase-octamer-binding fusion protein with a DNA-binding specificity indistinguishable from human HeLa cell Oct-1 protein. As expected for a ubiquitously expressed protein, Oct-1 mRNA is expressed in all five human and two mouse cell lines tested. Polyclonal rabbit antiserum raised against the beta-galactosidase fusion protein shows that the DNA-binding domains of Oct-1 and Oct-2 proteins are related antigenically. Deletion analysis of the 743-amino-acid-long oct-1 open reading frame shows that the DNA-binding activity lies within a central highly charged domain of 160 amino acids. Comparison of the Oct-1 and Oct-2 sequences reveals that this domain is nearly identical between the two proteins. Highly similar domains are also present in the pituitary-specific transcription factor Pit-1 and the Caenorhabditis elegans unc-86 cell lineage gene product (see Herr et al. 1988). Within this shared POU (Pit-1, Oct-1 and Oct-2, unc-86) domain (pronounced 'pow') lie two subdomains: a POU-related homeo box and a POU-specific box. The Oct-1 protein is unique among the POU-related proteins and other homeo box proteins because it is expressed ubiquitously.

Amino Acid Sequence↗
PubMed1988

Root formation in deteriorated (aged) wheat embryos.

Inability of aged seeds to grow into successful plants in the field is primarily due to their age-associated loss of rooting ability. The present work describes an attempt to initiate roots in nonrooting aged embryos of wheat (Triticum aestivum L.). Data presented give a comparative study of root formation and seedling growth on different culture media. Such studies indicate that sucrose alone is enough to bring about root development in nonrooting aged embryos.

Journal Article↗
PubMed1988

Tethered ureteric stents--a clinical assessment.

The acceptability and complications of tethered double-J stents were assessed in 17 patients. The study showed tethered ureteric stents to be safe, well tolerated and easy to remove. The technique avoids unnecessary ureteral instrumentation and general anaesthesia and has benefits for both patients and hospital resources.

Adolescent↗