No abstract

The aim of this work was to assess the possible correlation between oxidative damage and the development of cardiac hypertrophy in heart tissue from young (40-d-old) and older (4-, 11-and 19-month-old) spontaneously hypertensive rats (SHR) in comparison with age-matched Wistar (W) rats. To this end, levels of thiobarbituric acid reactive substances (TBARS), nitrotyrosine contents, NAD(P)H oxidase activity, superoxide production, and the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were determined. Compared to age-matched normotensive rats, SHR showed a significant increase in systolic blood pressure from 40 d of age and left ventricular hypertrophy (LVH) was significantly evident from 4 months of age. W rats (11-and 19-month-old) also showed an increase in LVH with aging. TBARS and nitrotyrosine levels were similar in young rats from both strains and were significantly increased with age in both strains, with the values in SHR being significantly higher than those in age-matched W rats. NAD(P)H activity was similar in young SHR and W rats, whereas it was higher in aged SHR compared with age-matched W rats. Compared to W rats, superoxide production was higher in aged SHR, and was abolished by NAD(P)H inhibition with apocynin. CAT activity was increased in the hearts of 4-month-old SHR compared to age-matched W rats and was decreased in the hearts of the oldest SHR compared to the oldest W rats. SOD and GPx activities decreased in both rat strains with aging. Moreover, an increase in collagen deposition with aging was evident in both rat strains. Taken together, these data showed that aged SHR exhibited higher cardiac hypertrophy and oxidative damage compared to W rats, indicating that the two undesirable effects are associated. That is, oxidative stress appears to be a cause and/or consequence of hypertrophy development in this animal model. (Hypertens Res 2008; 31: 1465-1476)

Growing in vitro evidence suggests NHE-1, a known target for reactive oxygen species (ROS), as a key mediator in cardiac hypertrophy (CH). Moreover, NHE-1 inhibition was shown effective in preventing CH and failure; so has been the case for AT1 receptor (AT1R) blockers. Previous experiments indicate that myocardial stretch promotes angiotensin II release and post-translational NHE-1 activation; however, in vivo data supporting this mechanism and its long-term consequences are scanty. In this work, we thought of providing in vivo evidence linking AT1R with ROS and NHE-1 activation in mediating CH. CH was induced in mice by TAC. A group of animals was treated with the AT1R blocker losartan. Cardiac contractility was assessed by echocardiography and pressure-volume loop hemodynamics. After 7 weeks, TAC increased left ventricular (LV) mass by ~45% vs. sham and deteriorated LV systolic function. CH was accompanied by activation of the redox-sensitive kinase p90(RSK) with the consequent increase in NHE-1 phosphorylation. Losartan prevented p90(RSK) and NHE-1 phosphorylation, ameliorated CH and restored cardiac function despite decreased LV wall thickness and similar LV systolic pressures and diastolic dimensions (increased LV wall stress). In conclusion, AT1R blockade prevented excessive oxidative stress, p90(RSK) and NHE-1 phosphorylation, and decreased CH independently of hemodynamic changes. In addition, cardiac performance improved despite a higher work load.

Living cells accumulate potassium (K⁺) to fulfil multiple functions. It is well documented that the model yeast Saccharomyces cerevisiae grows at very different concentrations of external alkali cations and keeps high and low intracellular concentrations of K⁺ and sodium (Na⁺) respectively. However less attention has been paid to the study of the intracellular distribution of these cations. The most widely used experimental approach, plasma membrane permeabilization, produces incomplete results, since it usually considers only cytoplasm and vacuoles as compartments where the cations are present in significant amounts. By isolating and analysing the main yeast organelles, we have determined the subcellular location of K⁺ and Na⁺ in S. cerevisiae. We show that while vacuoles accumulate most of the intracellular K⁺ and Na⁺, the cytosol contains relatively low amounts, which is especially relevant in the case of Na⁺. However K⁺ concentrations in the cytosol are kept rather constant during the K⁺-starvation process and we conclude that, for that purpose, vacuolar K⁺ has to be rapidly mobilized. We also show that this intracellular distribution is altered in four different mutants with impaired vacuolar physiology. Finally, we show that both in wild-type and vacuolar mutants, nuclei contain and keep a relatively constant and important percentage of total intracellular K⁺ and Na⁺, which most probably is involved in the neutralization of negative charges.

SUMMARYChlorella viruses are a source of interesting membrane transport proteins. Here we examine a putative K + transporter encoded by virus FR483 and related chlorella viruses. The protein shares sequence and structural features with HAK/KUP/KT-like K + transporters from plants, bacteria and fungi. Yeast complementation assays and Rb + uptake experiments show that the viral protein, termed HAKCV (high-affinity K + transporter of chlorella virus), is functional, with transport characteristics that are similar to those of known K + transporters. Expression studies revealed that the protein is expressed as an early gene during viral replication, and proteomics data indicate that it is not packaged in the virion. The function of HAKCV is unclear, but the data refute the hypothesis that the transporter acts as a substitute for viral-encoded K + channels during virus infection.

We report the characterization of five strains belonging to the halotolerant highly related Debaryomyces hansenii/fabryi species. The analysis performed consisted in studying tolerance properties, membrane characteristics, and cation incell amounts. We have specifically investigated (1) tolerance to different chemicals, (2) tolerance to osmotic and salt stress, (3) tolerance and response to oxidative stress, (4) reactive oxygen species (ROS) content, (5) relative membrane potential, (6) cell volume, (7) K(+) and Na(+) ion content, and (8) membrane fluidity. Unexpectedly, no direct relationship was found between one particular strain, Na(+) content and its tolerance to NaCl or between its ROS content and its tolerance to H(2)O(2). Results show that, although in general, human origin D. fabryi strains were more resistant to oxidative stress and presented shorter doubling times and smaller cell volume than food isolated D. hansenii ones, strains belonging to the same species can be significantly different. Debaryomyces fabryi CBS1793 strain highlighted for its extremely tolerant behavior when exposed to the diverse stress factors studied.

Saccharomyces cerevisiae cells are able to grow at very different potassium concentrations adapting its intracellular cation levels to changes in the external milieu. Potassium homeostasis in wild type cells resuspended in media with low potassium is an example of non-perfect adaptation since the same intracellular concentration is not approached irrespective of the extracellular levels of the cation. By using yeasts lacking the Trk1,2 system or expressing different versions of the mutated main plasma membrane potassium transporter (Trk1), we show that Trk1 is not essential for adaptation to potassium changes but the dynamics of potassium loss is very different in the wild type and in trk1,2 mutant or in yeasts expressing Trk1 versions with highly impaired transport characteristics. We also show that the pattern here described can be also fulfilled by heterologous expression of NcHAK1, a potassium transporter not belonging to the TRK family. Hyperpolarization and cationic drugs sensitivity in mutants with defective transport capacity provide additional support to the hypothesis of connections between the activity of the Trk system and the plasma membrane H(+) ATPase (Pma1) in the adaptive process.

No abstract