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General Physiology and Biophysics


Volume 26, 2007, No. 1

Content:


  Intrinsic defensive mechanisms in the heart: a potential novel approach to cardiac protection against ischemic injury
T. Ravingerová 1)

1)Institute for Heart Research, Centre of Excellence for Cardiovascular Research of Slovak Academy of Sciences, Bratislava, Slovakia..


Despite recent advances in pharmacotherapy of coronary artery disease and interventional cardiology, the management of myocardial ischemia still remains a major challenge for basic scientists and clinical cardiologists. An urgent need to combat ischemic heart disease, its forms, such as infarction, and complications including sudden cardiac death led to the development of an alternative strategy of myocardial protection based on the exploitation of the heart’s own intrinsic protective mechanisms. A new concept relies on the evidence that the heart is able to protect itself by way of adaptation, either short-term or long-term, to transient episodes of stress (e.g., ischemia, hypoxia, free oxygen radicals, heat stress, etc.) preceding sustained ischemia. Preconditioning by brief episodes of ischemia (ischemic preconditioning, IP) represents the most powerful cardioprotective phenomenon. Apart from the short-lasting protection afforded by classical IP or its delayed (“second window”) phase, adaptation to long-lasting physiological stimuli or pathological processes is also known to increase myocardial resistance to ischemic injury. Although molecular mechanisms of cardiac adaptation conferring a higher ischemic tolerance still remain not sufficiently elucidated, multiple cascades of intracellular signalization are suggested to be involved in this process. Experimental studies led to the observations that pharmacological modulations at different levels of signal transduction might mimic protective effects of the adaptive phenomena and thus provide a safer way of inducing cardioprotection in humans.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 3-13.

 
  Effects of β-hydroxybutyric acid on bovine milk leukocytes function in vitro
S. Cerone 1), A. Sansinanea, M. García

1)Departamento de Fisiopatología, Facultad de Cs. Veterinarias, UNCPBA, Tandil, Buenos Aires, Argentina..


The in vitro effect of different concentrations of β-hydroxybutyric acid (βHBA) on bovine milk leukocytes was examined. βHBA level similar to those found in cows with clinical ketosis in-duced a significant inhibitory effect on the nitroblue tetrazolium reduction as a mean of assaying the metabolic integrity of macrophages after the phorbol-mirystate- acetate and opsonized zymosan stimulation. In the same way, the H2O2 production after stimulation with both soluble and par-ticulate agents decreased significantly in 33 and 26%, respectively, compared with cells incubated without ketone bodies. This result suggests a possible fault in the microbicidal oxidative activity. The macrophage phagocytosis also decreased in cells treated with different βHBA concentrations, in relation to that obtained from control cells. Neutrophils migration in agarose was determined, and the mean chemotactic response was higher when the cells were incubated with lower level or absence of ketone bodies. Considering the determined differences, we hypothesize that abnormally high levels of ketone bodies could produce a direct effect on leukocyte membranes. The induction of some modification on the receptor structure impairment the interaction ligand-receptor and this may be, in part, responsible for the higher susceptibility to local infections in mammary gland during subclinical and clinical ketosis.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 14-19.

 
  Lidocaine alters the input resistance and evokes neural activity in crayfish sensory neurons
M. Keceli 1), N. Purali

1)Hacettepe University, Medical Faculty, Department of Biophysics, Sihhiye, Ankara, Turkey..


Lidocaine, a use-dependent Na+ channel blocker, paradoxically evokes neural activation in the slowly adapting stretch receptor organ of crayfish at 5–10 mmol/l concentration. For elucidating the underlying mechanisms of this paradoxical effect, a series of conventional electrophysiological experiments were performed in the stretch receptor neurons of crayfish. In the presence of tetrodo-toxin, lidocaine did not evoke impulse activity, however, a slowly developing and dose-dependent depolarization occurred in both the rapidly and slowly adapting stretch receptors. Similar effects were observed by perfusion of equivalent concentrations of benzocaine but not of procaine or prilocaine. Lidocaine did not evoke neural activity in the rapidly adapting neuron which fires action potential(s) in response to rapid changes in membrane potential. Slowly developing mode of the depolarization indicated the reason why only depolarization but not action potential responses were observed in the rapidly adapting neuron. The depolarizing effect of lidocaine was independent from any ionic channel or exchanger system. However, lidocaine and benzocaine but not procaine and prilocaine evoked a dose-dependent alteration in the input resistance of the neuron. It was proposed that the principal mechanism of the effect could stem from a change in the physical properties of the neu-ronal membrane.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 20-26.

 
  Cardiovascular diseases and molecular variants of the renin-angiotensin system components in Slovak population
D. Jurkovicova 1), B. Sedlakova, I. Riecansky, E. Goncalvesova, A. Penesova, R. Kvetnansky, O. Krizanova

1)Institute of Molecular Physiology and Genetics, Centre of Excellence for Cardiovascular Research of Slovak Academy of Sciences, Bratislava, Slovakia..


Cardiovascular diseases associated with molecular variants of individual components of renin-angiotensin system are reported to constitute inherited predisposition in humans. Molecular variant frequencies are race- and population-dependent. We examined frequencies of the M235T variant of angiotensinogen gene and I/D polymorphism of gene for angiotensin-converting enzyme in Slovak population: in hypertensive patients, coronary heart disease (CHD), dilated cardiomyopathy (DCM) and myocardial infarction (MI) patients compared to healthy subjects. Frequency of M235T was significantly increased in hypertensive, CHD and DCM patients compared to controls (0.48 and 0.50 vs. 0.40, p < 0.001). Significant increase in D allele frequency compared to controls was observed in the group of patients after MI (0.58 vs. 0.50, p < 0.001), CHD (0.59 vs. 0.50, p < 0.001) and DCM (0.60 vs. 0.50, p < 0.001). These results correlate with other Caucasian populations. In Slovak popu-lation, M235T is associated with increased blood pressure and D allele of ACE gene is associated with MI, chronic CHD and DCM, rather than with hypertension. Our results suggest that in Slovak population, D alelle and M235T variant represent a risk factor for several cardiovascular diseases and these polymorphisms might have a cumulative effect on development of cardiovascular diseases.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 27-32.

 
  Connexin 36 is expressed and associated with zonula occludens-1 protein in PC-12 cells
S. Lu 1), H. Li, F. Zhou, J. Zhang, L. Wang

1)Department of Histology and Embryology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China..


Connexin 36 (Cx36) is the predominant connexin isoform expressed in the mammalian neurons of the central nervous system (CNS). PC-12 cells, a neuronal-like cell line, are widely used for neuron functional studies. Many connexins have been shown to interact with zonula oc-cludens-1 protein (ZO-1), a tight junction associated with protein. The present study is intended to investigate whether Cx36 is expressed in PC-12 cells and is associated with ZO-1. Cx36 transcripts were amplified and verified by RT-PCR. 2.9 kb Cx36 mRNA was detected in PC-12 cells through Northern blot hybridization. Western blotting showed a 36-kDa protein band in the homogenates of PC-12 cells. Immunofluorescence labeling revealed that Cx36 was present in cell-cell contacts of PC-12 cells and colocalized with ZO-1. The association of Cx36 and ZO-1 in PC-12 cells was also demonstrated by coimmunoprecipitation. In conclusion, PC-12 cells express Cx36 mRNA and Cx36 proteins that are associated with ZO-1. These results enhanced our understanding of the function of Cx36 in PC-12 cells.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 33-39.

 
  Effect of temperature on plant elongation and cell wall extensibility
M. Pietruszka 1), S. Lewicka

1)Faculty of Biology and Environmental Protection, University of Silesia, Katowice, Poland..


Lockhart equation was derived for explaining plant cell expansion where both cell wall extension and water uptake must occur concomitantly. Its fundamental contribution was to express turgor pressure explicitly in terms of osmosis and wall mechanics. Here we present a new equa-tion in which pressure is determined by temperature. It also accounts for the role of osmosis and consequently the role of water uptake in growing cell. By adopting literature data, we also attempt to report theoretically the close relation between plant elongation and cell wall extensibility. This is accomplished by the modified equation of growth solved for various temperatures in case of two different species. The results enable to interpret empirical data in terms of our model and fully confirm its applicability to the investigation of the problem of plant cell extensibility in function of environmental temperature. Moreover, by separating elastic effects from growth process we speci-fied the characteristic temperature common for both processes which corresponds to the resonance energy of biochemical reactions as well as to the rapid softening of the elastic modes toward the high temperature end where we encountered viscoelastic and/or plastic behavior as dominating. By introducing analytical formulae connected with growth and elastic properties of the cell wall, we conclude with the statement how these both processes contribute quantitatively to the resonance-like shape of the elongation curve. In addition, the tension versus temperature "phase diagram" for a living plant cell is presented.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 40-47.

 
  A lack of synergistic interaction between insulin and pioglitazone on reactivity of rat aorta from chronically high dose insulin-treated diabetic rats
M. Sahilli 1), A. Irat, A. Işik, C. Karasu, G. Ozansoy, N. Ari

1)Ankara University, Faculty of Pharmacy, Department of Pharmacology, Tandogan, Ankara, Turkey..


Our goal was to determine whether hyperinsulinaemic and diabetic state can affect vaso-depressor effects of insulin and pioglitazone (PIO), an insulin-sensitizing thiazolidinedione drug. For this purpose, we established an experimental type 2 diabetic model (streptozotocin-nicotinamide model) in adult male rats (DIA group) and some of them were treated with chronically high-dose insulin for 14 weeks (INS-T DIA group). Blood pressure, glucose, HbA1C, triglyceride, cholesterol, plasma insulin levels and body weight were measured. Endothelium-denuded aortic rings were sus-pended in tissue baths for reactivity studies. Cumulative concentration-response curves of serotonin (5-hydroxytryptamine; 5-HT) were evaluated before and after 1 h incubations with insulin (10–7 or 10–4 U/l), or PIO (10 µmol/l) or insulin plus PIO. PIO or higher concentration of insulin (10–4 U/l), each alone, attenuated 5-HT induced contractions in both groups of aortae. Vasodepressor effect of insulin was diminished by 12% ± 4% in aortae from INS-T DIA group. The presence of PIO in the bath did not affect impaired vasodepressor response of insulin. Contractions induced by KCl, or Bay K 8644 were partly inhibited after PIO incubations, with similar Emax and pD2 values in both groups of aortae. The results indicate that PIO does not modulate directly vasodepressor effect of insulin in hyperinsulinaemic/diabetic state. But, the direct vasodepressor effect of PIO, partly by Ca2+ channel inhibition, may be beneficial by improving insulin utilization due to increasing blood flow to the insulin-sensitive tissues in hyperinsulinaemic/diabetic state.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 48-55.

 
  Glucocorticoid receptor represses the Dex-mediated induction of human androgen response element-linked Luc activity
M. Jang 1), K. Chae, D. Hwang, C. Kim, B. Kim, S. Shim, S. Jee, S. Lee, J. Shin, N. Chung, J. Cho, S. Choi, Y. Kim

1)Division of Laboratory Animal Resources, National Institute of Toxicological Research, Korea Food and Drug Administra-tion (KFDA), Seoul, Korea..


A human androgen response element (hARE), identified within intron 8 of the human sterol regulatory element-binding protein cleavage-activating protein, interacts with both glucocorticoid receptor (GR) and androgen receptors (AR). The aim of this study was to test the hypothesis that human GR (hGR) might modulate the expression of a hARE-linked reporter gene by dexamethasone (Dex). The hypothesis was tested by: a) co-transfecting HepG2 cells with a hGR and a luciferase (Luc)-reporter gene for performing in vitro investigations and b) by their co-injection into the tail vein of mice for in vivo investigation. In vitro co-transfected cells and the in vivo co-injected mice were then treated with Dex. Our results have led us to concluded that both transfection and injection of the hGR leads to a repression in the Dex-mediated induction of hARE-linked Luc activity both in vitro and in vivo settings. These findings suggest that this assay system allows screening of drug candidates affecting to a signal transduction pathway of the GR and AR and may help in the future discovery and analysis of novel and selection of GR and AR agonists.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 56-61.

 
  Proguanylin: development, analytical characterization, and clinical testing of a new ELISA
D. Stejskal 1), P. Solichová, B. Lacnak, J. Vaclavik, Z. Hanulova, V. Humeňanská, L. Sprongl, M. Karpíšek

1)Department of Laboratory Medicine and Internal Department, Šternberk Hospital, Czech Republic..


The aim of our work was to develop an assay for the determination of proguanylin in human blood, and investigate its levels in healthy volunteers and donors suffer from hypertension often accompanied by body sodium accumulation and plasma volume expansion. We developed and evaluated the sandwich ELISA method for the quantitative determination of human proguanylin in serum samples. We conducted also the pilot study on individuals with hypertension and oh healthy probands and measured proguanylin serum levels, serum and urine sodium and creatinine levels. In the study on 256 healthy volunteers we demonstrated that women have significantly higher values of proguanylin than men (medians 12.7 vs. 9.6 ng/ml, p < 0.01) and proguanylin values increased with age of individuals (p < 0.01). Futhermore, we tested 17 individuals with hypertension and found that probands with anamnesi of hypertension had higher proguanylin values than healthy individuals from the first study (medians 16.2 vs. 11.3 ng/ml, p < 0.01). Both of groups did not differ in sex or age. Proguanylin values correlated with the systolic blood pressure (r = 0.41, p < 0.01), sodium fraction excretion (r = 0.72, p < 0.01) and serum sodium (r = −0.39, p < 0.01). No significant correlation we found with serum proguanylin and creatinine. In the group of 9 healthy probands we demonstrated the existence of a diurnal rhythm of proguanylin with its maximum in the evening hours (between 6–10 p.m.). The pilot study supports the hypothesis about the role of proguanylin in sodium metabolism and its possible importance for hypertension disorder. Further research is necessary to confirm our findings in individuals with hypertension with different medication in order to assess proguanylin value as a risk predictor of accelerated hypertension, and to classify individuals with hypertension for variuos types of diuretic therapy.

General Physiology and Biophysics. Volume 26, 2007, No. 1: 62-65.