[Morphological Features of the Transgenic Tobacco Plant Shoot Expressing the 3-Hydroxy-3-Methylglutagyl-CoA Reductase (HMG1) Gene in the Direct and Reverse Orientations Towards the Promoter].

3-Hydroxy-3-methylglutaryl-CoA reductase (HMG1) catalyzes the formation of mevalonic acid, the key intermediate of the cytosolic isoprenoid synthesis pathway. The parameters of stem and leaf growth were studied in the transgenic tobacco plants that express the HMG1 gene in both sense and antisense orientations towards the constitutive promoter. The transgenic plant height did not significantly differ from that of the control plants, though the plants carrying the sense copy of the HMG1 gene were considerably taller than plants that carried the antisense gene copy. Plants carrying an extra copy of the HMG1 gene were also characterized by increased leaf area. The number of mesophyll cells calculated per square unit of transgenic plants leaves was smaller than in the control plant leaves, though their volume was not considerably changed in any of the variants, suggesting changes in the cell packing density in leaves.

Role of nitric oxide in activity control of mechanically gated ionic channels in cardiomyocytes: NO-donor study.

Whole-cell ionic currents through mechanically gated channels (MGC) were recorded in isolated cardiomyocytes under voltage clamp conditions. In unstrained cells, NO donors SNAP and DEA-NO activated MGC and induced MG-like currents. In contrast, in stretched cells with activated MGC, these NO-donors inactivated and inhibited MGC.

Role of nitric oxide in the regulation of mechanosensitive ionic channels in cardiomyocytes: contribution of NO-synthases.

The role of NO in the regulation of currents passing through ion channels activated by cell stretching (mechanically gated channels, MGC), particularly through cation-selective K(+)-channels TRPC6, TREK1 (K(2P)2.1), and TREK2 (K(2P)10.1), was studied on isolated mouse, rat, and guinea pig cardiomyocytes using whole-cell patch-clamp technique. In non-deformed cells, binding of endogenous NO with PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-1-oxy-3-oxide) irreversibly shifted the diastolic membrane potential towards negative values, modulates K(ir)-channels by reducing I(K1), and blocks MGC. Perfusion of stretched cells with PTIO solution completely blocked MG-currents. NO-synthase inhibitors L-NAME and L-NMMA completely blocked MGC. Stretching of cardiomyocytes isolated from wild type mice and from NOS1(-/-)- and NOS2(-/-)- knockout mice led to the appearance in MG-currents typical for the specified magnitude of stretching, while stretching of cardiomyocytes from NOS3(-/-)- knockout mice did not produce in MG-current. These findings suggest that NO plays a role in the regulation of MGC activity and that endothelial NO-synthase predominates as NO source in cardiomyocyte response to stretching.

[Voltage-gated calcium channels].

The article concentrates on representatives of voltage-gated calcium ion-channels that are present in practically all cells. Considered are the activation and inactivation processes of calcium channels and their molecular mechanisms. The review represents modem classification of voltage-gated calcium channels, draws parallels with the earlier classifications and discusses calcium currents going through various calcium channels. Presented are the genetic, molecular-biological, bio-physical, physiological and pharmacological information for each type of the ten known voltage-gated calcium channels.

[Voltage-gated calcium channels].

The article concentrates on representatives of voltage-gated calcium ion channels that are present in practically all cells. Regarded is the molecular arrangement of a voltage-gated calcium channel that consists of pore forming trans-membrane alpha1 subunit and auxiliary alpha2delta-, beta-, and gamma-subunits. Under discussion are the structure and functions of each subunit. The principles of subunits interaction are considered. The research represents modern classification of voltage-gated calcium channels, draws parallels with the earlier classifications and discusses calcium currents going through various calcium channels. Considered are the problems of regulating the activity of voltage-gated channels by proteinkinases. The issues of blockers and activators of voltage-gated calcium channels are brought up. The article gives a detailed analysis of the mechanisms of voltage-gated calcium channels selectivity. The molecular organization of the selectivity filter is considered. Presented are the basic theories of permeability of voltage-gated calcium channels.

[Mechanosensitive ion channels]. / Mekhanosensitivnye ionnye kanaly.

The article concentrates on the concepts of mechanosensitive ion channels that are present in practically all cells of an organism. Considered are kinetic scheme and activation principles of mechanic-sensitive ion channels. The forces affecting those channels are discussed in detail. The qualities of the channels in lipid monolayer, bilayer and real cell membrane are under consideration. Discussed are various models that analyze possibilities of channel opening depending on the membrane tension. Under discussion are the data received from studying single channels, currents in whole-cell configuration and cloned channels built into bilayer, liposomes and membrane blebs. Problems of transmitting mechanic energy to the channel through the bilayer and through the cytoskeleton are investigated. Inhibitors and activators of mechanosensitive ion channels are mentioned and their effects are considered. The functional classification of mechanosensitive ion channels is given. Described are cation SACs, potassium SACs, Ca(2+)-sensitive and Ca(2+)-insensitive SACs, anion SACs, nonselective SACs and SICs. It is proved that mechanosensitive ion channels can produce considerable currents enough to change the cell electrogenesis.

[Ion mechanisms of the mechanoelectrical feedback in myocardial cells]. / Ionnye mekhanizmy mekhanoélektricheskoi obratnoi sviazi u kletok serdtsa.

This article is dedicated to the mechanism of mechano-electric feedback in heart. The evidence is briefly discussed on organ, tissue, cell and in details on cell membrane levels in case of application of one of applied mechanical stimulus to cardiomyocytes. Stretch of the hole heart or its tissue fragment causes quick starting repolarization of action potentials (AP)/monophasic action potentials (MAP), shift of AP/MAP plato to higher negative zone, appearance of peaks of stretch-induced depolarization (SID) on final phase of AP/MAP repolarization level, which are overgrowing into extra AP/extra MAP. Mechanical events (changes in length and force of contractions) change electrical processes by means of direct influence on cell membrane via stretch activated channels (SAC). Cardiomyocytes, isolated from animal atrium and animal and human ventricular are responsible for the stretch of depolarized membrane, prolongation of AP and appearance of extra AP (extra systoles). Analysis of experiments, conducted following the patch clamp method in whole cell configuration, shows that the main cause of that mechanical events is SAC current--ISAC. During negative potential ISAC is determined by incoming into the cell sodium ions and is negative. Negative ISAC is changing final phase of AP/MAP repolarization and causes SID, which is overgrowing into extra AP (extra systoles), in case that SID exceeds threshold. Fast AP repolarization and AP plato shift into higher negative zone is related to positive ISAC (living potassium ions through SAC), activation of IK and reduction of ISAC. Activation of ISAC and arrhythmia induction require lower mechanical stimulus for hypertrophied cardiomyocytes, in comparisment to healthy ones. Hypertrophy of cardiomyocytes can lead to expression of SAC therefore increasing channel density and ISAC maximum amplitude. In this article is discussing data, acquired by means of direct measurement of conduction of single SAC on the background of mechanical stimulation of the cardiomyocytes membrane. It contains characteristics of the estimated SACs. It is shown that blocking of conduction of ions through SAC prevents mechanically induced arrhythmia in healthy and hypertrophied cardiomyocytes, which transforms the problem of mechano-electric feedback in heart from purely fundamental into clinical one.

[Mechanoelectrical feedback in the healthy heart and in the heart with pathologies]. / Mekhanoélektricheskaia obratnaia sviaz' v zdorovom serdtse i serdtse s nekotorymi patologiiami.

The article discusses the issues of possible connection between mechanical phenomena in myocardium and the electrical processes. Not only cardiomyocytes, but also cardiac fibroplastic are considered as substratum for the mechanisms of mechano-electrical feedbacks. Cardiomyocytes and fibroplastic of healthy animals demonstrate the mechano-electrical feedbacks, which essentially mean that stretching of the cardiac tissue within the physiological limits to 2 mN changes the electrophysiological cell processes. Close to 90% repolarization potential of cardiomyocytes action the mechano-induced depolarization develops; over the background of depolarization, when it reaches the threshold values, extra potentials of action are generated. In fibroplastic, membrane mechano-induced hyperpolarization develops; as result of cellular interaction it may develop hyperpolarization of pacemaking cells of the right auricle and slow the cardiac rythm down. In case of a pathology, for instance, infarct of the left heart ventricle modification of electric cell activity was detected at quite low values of tissue stretching up to 0.2. mN. Mechano-induced depolarization of cardiomyocytes of animals affected by infarct develops at 50% level of repolarization phase of action potential, or at 90% of repolarization phase. In the former case development of mechano-induced depolarization coincides with the period of absolute cell refractering. Extra action potential develops immediately after the refractering phase when the mechano-induced depolarization shifts the membrane potential towards threshold values. In the latter case the mechano-induced depolarization transforms into extra action potential. With further stretching fibrillation develops. In fibroplastic the values of mechano-induced membrane hyperpolarization grow with greater scope of infarct damage. Magnitude of mechano-induced hyperpolarization of auricle fibroplastic taken from the animals with infarcts shows dependence on the period of remodelling if stretching is tissue is a standard parameter. With prolongation of the remodelling period the value of mechano-induced fibroplastic hyperpolarization diminishes. The problem of developing the combinations eliminating mechano-induced cardiac arrhythmia is raised.

[Heart fibroblasts, the mechanism of the appearance of their potentials and their possible role in regulating cardiac work]. / Serdechnye fibroblasty, mekhanizm vozniknoveniia ikh potentsialov i vozmozhnaia rol' v reguliatsii raboty serdtsa.

Electrically non-excitable fibroblasts, which represent the other population of cells abundant in the sino-atrial node region, have been reported to be mechanosensitive in the frog and in the rat heart. It was shown that these cells respond to artificial or contraction-induced stretch of the atrial wall by a change in membrane potential. These changes could be explained by the operation of stretch-activated channels and intracellular calcium oscillation. Influences of cardiac fibroblasts on electrophysiological properties of cardiomyocytes would require interaction between these cells. In tissue culture studies, it has been shown, that fibroblasts and cardiomyocytes form nexus connections. In recent studies on fibroblast-cardiomyocyte junctions in the rabbit heart pacemaker region, non nexus-like contacts clearly dominated. These membrane non nexus-like contacts might promote capacitive interactions between heterologous cells, which has been demonstrated independently in electrophysiological studies. Through these contacts, the fibroblast membrane potential may affect the membrane potential of neighbouring myocytes in the right atrium which may play an important role for the chronotropic response of the heart to mechanical stretch of the right atrial wall. Electrically non-excitable but mechanosensitive cardiac fibroblasts can act as a substrate for an intracardiac mechano-electrical feedback mechanism by which mechanical changes, e.g. stretch, modulate the electrical activity. In the atria, fibroblasts may act as volume and mechanical sensors, respectively.

Mechanosensitive fibroblasts in the sino-atrial node region of rat heart: interaction with cardiomyocytes and possible role.

The positive chronotropic response of the heart to stretch of the right atrium is one of the major mechanisms adjusting the heart rate to variations in venous return on a beat-by-beat basis. The precise pathway of this mechano-electric feedback and its cellular basis are uncertain. In this study, a possible contribution of mechanosensitive fibroblasts, abundant in the sino-atrial node region, was investigated using a mathematical model of the electrical interaction of a mechanosensitive fibroblast and a sino-atrial pacemaker cell. Electrophysiological evidence for a bio-electrical interaction of mechanosensitive fibroblasts with surrounding cardiomyocytes has been studied in (i) the isolated spontaneously beating atrium of rat hearts, and (ii) cell cultures of the neonatal rat heart. These investigations were performed using (i) double-barrelled floating microelectrodes for intracellular potential registrations, and (ii) the double whole cell patch-clamp technique. It was shown that cardiac fibroblasts and surrounding cardiomyocytes can be either electrically well isolated from each other, or coupled both capacitively and electrotonically. The electrophysiological data obtained were incorporated into the OXSOFT HEART program. Assuming that equivalent coupling may occur between mechanosensitive fibroblasts and sino-atrial pacemaker cells, a heterologous cell pair consisting of one fibroblast and one sino-atrial node myocyte connected by ten to thirty single gap junctional channels with a conductance of 30 pS was modelled. The model of the electrotonic interaction of these cells showed that stretch of the fibroblast during atrial diastole, simulating increased atrial wall tension during atrial filling, can raise the spontaneous depolarization rate of the pacemaker cell in a stretch-dependent manner by up to 24%. These results show that cardiac mechanosensitive fibroblasts could form a cellular basis for the positive chronotropic response of the heart to stretch of the right atrium.

Mechanosensitive cells in the atrium of frog heart.

Mechanosensitive cells were found in the sinus venosus and right atrium of the frog heart. Their intracellular membrane potentials were studied in spontaneously beating hearts and in artificially stretched preparations. Membrane resistance was indirectly proportional to the stretch applied. The electrophysiological data and distribution of these cells in the heart led to the conclusion that they are cardiac fibroblasts.

[Role of ACTH fragments in regulating electrogenesis and electrotonic synaptic interaction of pond snail neurons]. / Rol' fragmentov AKTG v reguliatsii élektrogeneza i élektrotonicheskogo sinapticheskogo vzaimodeistviia neironov ulitki prudovika.

The hypothesis of neuropeptides involvement in intercellular interaction was checked on the neurons VD1 and RPD2 connected with electrotonic synapse with two-way transmission in nerve ganglia of the pond snail. The preparation was perfused with natural and synthetic fragments of ACTH (2 X 10(-7) M). In perfusion with ACTH4-10 solution, synapse became rectified whereas in ACTH4-7 and ACTH5-10 solutions it obtained partially rectified properties. After exposure to ACTH4-7--Pro--Gly--Pro, synapse obtained rectifying properties with one--way increase in conductivity following temporary two-way increase of transmission efficiency. With the use of Pro--Gly--Pro--ACTH4-7--Pro--Gly--Pro, inhibition of the two--way conductivity occurred. Neuropeptides seem to modulate synaptic transmission. Impulse priority depends on the initial level of the cell MPs and is purposefully modulated by the peptides under test.