P2559The mechanisms of spontaneous action potential generation in sinoauricular valve of the chick embryos

Background

The changes in the density of ion channels and/or damage of ion channel proteins violates the homeostasis of the potential forming ions in myocardium cells and may contribute to arrhythmogenesis. The study of ion channel function in embryos is important in order to understand the mechanisms of arrhythmia.

The purpose of the present study was to identify the key ion channels that form action potentials (APs) in pacemaker cells in the area of the sinoauricular (SA) chicken embryo valve.

Material and methods

The embryos were removed from fertilized White Leghorn breed chicken eggs on the 10±1 day of incubation (ED10). The experiments were performed on freshly prepared strips (3 mm × 2 mm) of the right atrium, which included the left SA valve itself as well as the surrounding tissue. After that the APs were recorded from the area of left SA valve using the microelectrode technique. The functional analysis of ion channels was performed using the specific ion channel blockers.

Results

The strips generated APs with slow diastolic depolarization (SDD) and frequency from 132 to 251 impulses per min (ipm) (average - 177±22 ipm). The APs amplitude and dV/dtmax were 102±9 mV and 98±25 V/s (nstrips=49). At the third minute of exposure to E-4031 (1 μmol), a blocker of rapid outward K-current channels, IKr, the increase in the duration of the AP repolarization phase by 30% and the shortening of SDD by 20–25% (p<0.05; n=6) were registered. The APs generation frequency increased by 10%. Subsequently we observed the monotonic decrease in the AP amplitude due to the reduced overshoot and depolarized Emax. The electrical activity of all strips was blocked on the 20±2 min (Fig.1.a-c). Lidocaine (500 μmol), a blocker of Nav1.5 channels, increased a duration of SDD and APD90 twice, but decreased dV/dtmax by 2.5 times. The APs generation frequency decreased by 30% in comparison to the control. After 8±2 min exposure to lidocaine, the APs generation was blocked in 56% of samples. It is important to mention that in these strips right before the APs generation was blocked dV/dtmax was 30±15 V/s. In the samples, where the APs were not blocked after the exposure to lidocaine this parameter was 14±10 V/s (Fig. 1d-e). Nifedipine (10 μmol), a blocker of L-type Ca2+-channels, decreased APD90 by 56% and SDD by 25%. The APs generation frequency increased twice in comparison to the control samples (fig.1f-h). The chronotropic effects of nifedipine were dose-dependent. Nifedipine did not induce the blocking of APs generation.

Figure 1. Effects of E-4031 (a-c), lidocaine (d-e) and nifedipine (e-g) on APs.

Conclusions

The received data demonstrate that the key role in the APs formation in ED10 embryos belong to the outward IKr and inward INa, but not to ICa,L. Thus, the mechanisms of spontaneous action potential generation in ED10 chick embryos have more in common with that in human iPSC-derived cardiomyocytes rather than in SA area cells of the ED11 mice embryos.

Acknowledgement/Funding

Rus fund Basic Research No. 18-34-00654; Project RAS No. 0415-2019-0006 and No. AAAA-A17-117012310152-2

Event reconstruction of free-streaming data for the RICH detector in the CBM experiment

The Compressed Baryonic Matter (CBM) experiment is a dedicated heavy ion collision experiment at the FAIR facility. It will be one of the first HEP experiments which works in a triggerless mode: data received in the DAQ from the detectors will not be associated with events by a hardware trigger anymore. All raw data within a giventime period will be collected continuously in containers, so-called time-slices. The task of the reconstruction algorithms is to create events out of this raw data stream. In this contribution, the optimization of the reconstruction software in the RICH detector to the free-streaming data flow is presented. The implementation of ring reconstruction algorithms which use time measurements of the hits as an additional parameter is discussed.

Genetic variants of the insulin receptor substrate-1 are influencing the therapeutic efficacy of oral antidiabetics

AIM

The therapeutic efficacy of oral hypoglycaemic drugs varies between individuals, and pharmacogenetic factors contribute to this variability. The Gly972Arg polymorphism in the insulin receptor substrate-1 (IRS-1) has been shown to play a role in insulin signal transduction and therapeutic failure to sulphonylurea drugs.

METHODS

We studied the association between the IRS-1 polymorphism and the haemoglobin A1c (HbA1c) level in diabetic patients treated with insulinotropic versus non-insulinotropic hypoglycaemic drugs as a marker for the efficacy of an antidiabetic treatment. Genotyping of the IRS-1 Arg(972) variant was performed in type 2 diabetes patients treated with either sulphonylurea drugs, glinides or insulin or with metformin, acarbose or glitazones using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Significantly higher HbA1c levels were observed in carriers of the Arg(972) variant after treatment with insulinotropic drugs compared to wild-type carriers (8.3 vs. 7.6%, p = 0.005, independent t-test). Furthermore, patients with secondary failure to insulinotropic hypoglycaemic drugs switching finally to insulin showed even higher HbA1c levels in carriers of Arg(972) compared to wild-type (8.7 vs. 7.6%, p = 0.005, independent t-test).

CONCLUSIONS

Thus, we were able to replicate the earlier findings of an association between the IRS-1 Arg(972) variant and secondary failure to sulphonylurea drugs, and further observed a general association between HbA1c and this polymorphism in type 2 diabetes patients treated with insulinotropic hypoglycaemic drugs but not with metformin.

A novel presenilin1 mutation (Q223R) associated with early onset Alzheimer's disease, dysarthria and spastic paraparesis and decreased Abeta levels in CSF

BACKGROUND AND PURPOSE

A novel presenilin1 (PSEN1) mutation associated with dementia and spastic paraplegia in a family with five affected individuals is described. The index patient was a 35-year-old man presenting with cognitive decline, behavioural symptoms, dysarthria, and gait disorder due to spasticity.

METHODS AND RESULTS

Genetic analysis revealed a missense mutation Gln223Arg in exon 7. Initial CSF analysis revealed drastically decreased Abeta42 level despite marginally decreased FDG metabolism.

CONCLUSION

Cerebrospinal fluid biomarker analysis might point towards genetic analysis of PSEN1 in patients with positive family history and age of onset below 60 years.

A new obligately chemolithoautotrophic, nitrite-oxidizing bacterium, Nitrospira moscoviensis sp. nov. and its phylogenetic relationship

A gram-negative, non-motile, non-marine, nitrite-oxidizing bacterium was isolated from an enrichment culture initiated with a sample from a partially corroded area of an iron pipe of a heating system in Moscow, Russia. The cells were 0.9-2.2 microns x 0.2-0.4 microns in size. They were helical- to vibroid-shaped and often formed spirals with up to three turns 0.8-1.0 micron in width. The organism possessed an enlarged periplasmic space and lacked intracytoplasmic membranes and carboxysomes. The cells tended to excrete extracellular polymers, forming aggregates. The bacterium grew optimally at 39 degrees C and pH 7.6-8.0 in a mineral medium with nitrite as sole energy source and carbon dioxide as sole carbon source. The optimal nitrite concentration was 0.35 mM. Nitrite was oxidized to nitrate stoichiometrically. The doubling time was 12 h in a mineral medium with 7.5 mM nitrite. The cell yield was low; only 0.9 mg protein/l was formed during oxidation of 7.5 mM nitrite. Under anoxic conditions, hydrogen was used as electron donor with nitrate as electron acceptor. Organic matter (yeast extract, meat extract, peptone) supported neither mixotrophic nor heterotrophic growth. At concentrations as low as 0.75 g organic matter/l or higher, growth of nitrite-oxidizing cells was inhibited. The cells contained cytochromes of the b- and c-type. The G+C content of DNA was 56.9 +/- 0.4 mol%. The chemolithoautotrophic nitrite-oxidizer differed from the terrestrial members of the genus Nitrobacter with regard to morphology and substrate range and equaled Nitrospira marina in both characteristics. The isolated bacterium is designated as a new species of the genus Nitrospira.(ABSTRACT TRUNCATED AT 250 WORDS)