Rita Papp

Method for measuring neurotoxicity of aggregating polypeptides with the MTT assay on differentiated neuroblastoma cells

Reliable in vitro assays are essential for study of the effects of neurotoxic compounds such as beta-amyloid peptides (Abeta). The MTT assay has been used in cultures of different cells, e.g. SH-SY5Y neuroblastoma cells, for the quantitative measurement of Abeta toxicity. In our laboratory differentiated SH-SY5Y cells were used in the MTT assay. Cell differentiation with 10 microM all-trans-retinoic acid resulted in a constant cell number. The cells possess highly developed neurites and exhibit high sensitivity against Abeta. Owing to the constant cell number in differentiated SH-SY5Y cultures the decrease of the redox activity is directly proportional to the neurotoxicity of the substances, no correction is needed. The results of the MTT assay of Abeta peptides on differentiated SH-SY5Y cells displayed a good correlation also with the in vivo results. The present experiments reveal an effective assay for the study of potentially neurotoxic compounds.

Modulation of gap junctions by nitric oxide contributes to the anti-arrhythmic effect of sodium nitroprusside?

Background and purpose:  Nitric oxide (NO) donors provide a preconditioning‐like anti‐arrhythmic protection in the anaesthetized dog. As NO may modulate gap junction (GJ) function, the present study investigated whether this anti‐arrhythmic effect is due to a modification of GJs by NO, derived from the NO donor sodium nitroprusside (SNP).

Analysis of the contribution of Ito to repolarization in canine ventricular myocardium

BACKGROUND AND PURPOSE The contribution of the transient outward potassium current (Ito) to ventricular repolarization is controversial as it depends on the experimental conditions, the region of myocardium and the species studied. The aim of the present study was therefore to characterize Ito and estimate its contribution to repolarization reserve in canine ventricular myocardium.

Changes in gene expression following cardiac pacing-induced delayed cardioprotection in the canine heart

The aim of the present study was to identify gene expression changes in the rapid cardiac pacing-induced delayed antiarrhythmic protection in the canine, using cDNA microarrays and quantitative real-time PCR (QRT -PCR) techniques. In all dogs under light pentobarbitone anaesthesia, a pacing electrode was introduced into the right ventricle, and then the animals were divided into three groups: (1) sham-operated and sham-paced group (SP, n = 3) (2) ischaemic control group (IC; n = 3); these were without cardiac pacing and subjected only to a 25 min occlusion of the left anterior descending coronary artery (LAD), and (3) paced group (PC, n = 3); these animals were paced at a rate of 220-240 beats min-1 24 h prior to ischaemia. With cDNA chip 23 genes were found with altered expression in response to rapid cardiac pacing and 10 genes in the IC group when compared to SP dogs. These genes encode transcription factors (MEF2); members of signaling pathways (TGFβ2, PDE4D9), hormone related proteins (e.g. vasopressin V1 and V2 receptors). RT-QPCR was used either to confirm the results of the microarray analysis and also to study 46 genes which are already known to have a role in the late phase of PC. By this method 17 genes were up-regulated and 6 genes down-regulated in the IC group; their expression ratios changed either to the opposite or showed no alteration after cardiac pacing. This study would add some new information about those transcriptional changes that are involved in the delayed phase of cardiac protection.

Possible Mechanisms of the Acute Ischemia-Induced Ventricular Arrhythmias: The Involvement of Gap Junctions

One of the most important consequences of abrupt reduction in coronary blood flow following coronary artery occlusion in experimental animals, and perhaps also in humans, is the occurrence of life-threatening ventricular arrhythmias, which are often responsible for sudden cardiac death. The reduced and inhomogeneously distributed blood supply creates rapid, tightly time-dependent and spatially heterogeneous metabolic, ionic, and electrophysiological alterations within the affected myocardial region. This tissue inhomogeneity is the most likely cause of acute ischemia-induced arrhythmias. These arrhythmias occur in two distinct phases: the first, phase 1A, is usually 3–8 min of ischemia during which reentrant mechanisms are most probably responsible for generating and sustaining arrhythmias. This is followed by a relatively quiet period during which, although the ischemia continues, arrhythmias occur less frequently. Processes during this arrhythmia-free interval, however, might be important in the generation of the second arrhythmia phase, (phase 1B). Phase 1B arrhythmias appear between 15 and 30 min of ischemia, and might be even more severe than those of phase 1A. Precise mechanism of phase 1B arrhythmias is still obscure, but their occurrence can be related to uncoupling of gap junctions (GJ). Consequently, modification of GJ coupling may provide an alternative approach to inhibit or at least attenuate these fatal ventricular arrhythmias. This chapter attempts to summarize briefly our recent knowledge on mechanisms underlying the acute ischemia-induced ventricular arrhythmias with particular reference to the role of cardiac GJs.