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A Popescu

Publications and source records attributed to A Popescu.

At least 37 records · Page 2Linked to original sources
PubMed1996

Acute simulated ischaemia produces both inhibition and activation of K+ currents in isolated ventricular myocytes.

OBJECTIVE: The aim was to investigate the effects of acute ischaemia on cardiac repolarizing K+ currents. METHODS: We developed a model of acute ischaemia in isolated rat ventricular myocytes transiently surrounded with a mineral oil droplet. During ischaemic challenges, we recorded intracellular pH using the fluorescent probe seminaphthorhodafluor-1 (SNARF-1) and whole-cell K+ currents using the patch-clamp technique. RESULTS: Decrease in intracellular pH (pH1) during simulated ischaemia was dependent upon the extracellular proton buffer used (pH1 decreased from 7.44 +/- 0.02 to 7.16 +/- 0.04 in a Hepes-buffered medium and from 7.08 +/- 0.04 to 6.56 +/- 0.07 with bicarbonate buffer). In Hepes, action potential duration initially lengthened and then shortened under the effects of ischaemia. Initial action potential duration lengthening was concomitant with a block of the inward rectifier K+ current, whereas late shortening corresponded with the activation of the ATP-sensitive K+ current. Similar changes occurred in bicarbonate buffer although with different amplitudes and kinetics. Patch-clamp experiments also showed inhibition of the transient outward K+ current. Brief transient episodes of ischaemia activated ATP-sensitive K+ current in only 20% of control cells (n = 21) but in 100% of cells treated with 15 microM cromakalim (n = 9). CONCLUSIONS: (i) Simulated ischaemia produces complex effects on repolarizing K+ currents including both inhibition and activation; (ii) cromakalim accelerates activation of ATP-sensitive K+ current during simulated ischaemia.

Action Potentials↗
PubMed1995

Calmodulin binding of a peptide derived from the regulatory domain of Bordetella pertussis adenylate cyclase.

This paper reports the solution conformation and calmodulin binding of a 43-residue peptide from the calmodulin-binding domain of Bordetella pertussis adenylate cyclase. The peptide (P225-267) was synthesized and 15N-labeled at specific amino acids. It binds calmodulin with an equilibrium dissociation constant of 25 nM. Assignment of the NMR spectrum of the free peptide and analysis of the NOE connectivities and secondary shifts of C alpha protons allowed us to identify a 10-amino acid fragment (Arg237 to Arg246) which is in rapid equilibrium between alpha-helical and irregular structures. Titration experiments showed that at substoichiometric molar ratios the two molecules are in intermediate exchange between free and bound conformations. Using 15N-edited methods we assigned a large part of resonances of the labeled residues in the bound peptide. Analysis of the chemical shift differences between free and bound states shows that the fragment Leu240-Ala257 is the most affected by the interaction. The proton spectra of the calmodulin, in the free and complexed states were extensively assigned using homonuclear experiments. Medium- and long-range NOE patterns are consistent with a largely conserved secondary and tertiary structure. The main changes in chemical shift of calmodulin resonances are grouped in six structural regions both in NH2- and COOH-terminal domains. Intermolecular NOE connectivities indicate that the NH2-terminal of the bound peptide fragment is engulfed in the COOH-terminal domain of calmodulin. The interaction geometry appears to be similar to those previously described for myosin light chain kinase or calmodulin kinase II fragments.

Adenylyl Cyclases↗
PubMed1992

Protective effect of oral acetylcysteine against the hepatorenal toxicity of carbon tetrachloride potentiated by ethyl alcohol.

Considering the well-documented protection of acetylcysteine (AC) in hepatotoxicity related to acetaminophen, we studied the preventive potential of AC against mild hepatotoxicity of CCl4, potentiated with ethyl alcohol (ETH) and the role of tissue glutathione. Rats fed a liquid diet with 30% of energy from ETH, had-intraperitoneal CCl4 administered in three injections, at 7-day intervals. AC was ingested at the level for acetaminophen overdose. ETH markedly potentiated the injury induced by CCl4, as evidenced by higher values of serum alanine aminotransferase (ALT), urinary bile acids (BA), serum creatinine, histological score of liver cell necrosis, mortality and by lower body weights and lower liver glutathione, when compared with CCl4 alone. Protective effect of AC consisted of a lesser hepatocytic necrosis, better body weights and higher liver glutathione. We conclude, that AC favorably modifies liver damage induced by CCl4 and potentiated with ETH. There is a preventive role for AC in subjects who combine ETH overuse with exposure to hepatotoxic xenobiotics, whose toxicity is modified by tissue glutathione.

Acetylcysteine↗
PubMed1990

Basal cell carcinoma. A population-based incidence study in Rochester, Minnesota.

Population-based annual incidence rates for histologically proved basal cell carcinoma were derived from the records linkage system of the Rochester Epidemiology Program Project. Residents of Rochester, Minnesota, during the years 1976 to 1984, formed the observational cohort. A total of 657 first episodes of basal cell carcinoma were observed. Annual incidence rates per 100,000 persons in the Rochester population, standardized to the 1980 U.S. white population, were 175 for men, 124 for women, and 146 combined. Recurrent or subsequent basal cell carcinoma was observed among 30% of patients during an average of 4.5 years of follow-up; no metastatic lesions occurred. The rates of recurrence were similar after complete excision or treatment with curettage and cauterization in these observational data.

Aged↗
PubMed1980

[Not Available].

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History, Early Modern 1451-1600↗
PubMed1979

Lethal effect of protamine and histone on competent Bacillus subtilis cells. Inhibition of genetic transformation by protamine in sublethal concentration.

Under experimental conditions of genetic transformation, protamine and total histone were bactericidal for Bacillus subtilis cells. The abilities to cause lethality were very similar for both, either protamine or histone, with no antagonistic effects amongst these natural polycations. With both basic proteins acting simultaneously the enhancement was higher than a summation of the separate lethal effects. Sublethal concentration of protamine added at the beginning of transformation time, produced a strong inhibition of transforming efficiency. The same concentration added later than 10 min from the start of transformation had no inhibitory effect. These facts together with the absence of inhibition by simple pretreatment of DNA alone as well as the cell protection by protamine against lytic activity of lysozyme, suggest a protamine-cell surface interaction which impedes DNA uptake events.

Bacillus subtilis↗
PubMed1979

Protamine and polyarginine bacteriolysis. Similarities in its mechanism with chromatin DNA picnosis.

Protamine and polyarginine had bacteriolytic effects indicating their primary sites of action as being wall components and showing bacterial diversity genetically determined. Shake-incubation was required in producing cell-lysis. Studies on Bacillus subtilis revealed a high polycation multiplicity per cell in lytic event displaying multihit lysing kinetics; bacteriolysis was inhibited by trypsin, pronase, purified polyanionic wall polysaccharide, and by dissociative actions of salt hypermolarities used in isolation of nucleic acids. The inactivation of polycation lytic abilities during bacteriolysis was accompanied by modifications in electrophoretic running of protamine and polyarginine. It is suggested as mechanism of cell-lysis, the multiple zonal surface condensations of polyanionic wall components by basic polypeptides, likely similar with chromatin DNA picnosis. This analogy is discussed.

Anti-Bacterial Agents↗
PubMed1975

Experimental research on endotoxic shock in urology.

The endotoxic shock in urological surgery is more frequent due to the increased incidence of the gram-negative infections. More toxic than septic it suggests the hypothesis of a generalized Sanarelli-Schwartzman hypersensitivity phenomenon with hypercoagulation and microthromboses of small vessels. The hypothesis experimentally tested hold good in most cases at the same time requiring an anti-coagulant therapy as an improving effect.

Animals↗