Protein kinase C-mediated calcium signaling as the basis for cardiomyocyte plasticity.

Protein kinase C is the superfamily of intracellular effector molecules which control crucial cellular functions. Here, we for the first time did the percentage estimation of all known PKC and PKC-related isozymes at the individual cadiomyocyte level. Broad spectrum of PKC transcripts is expressed in the left ventricular myocytes.

Cardiomyocytes generating spontaneous Ca-transients as tools for precise estimation of sarcoplasmic reticulum Ca transport.

Spontaneous Ca-transient (wave) generation in isolated cardiomyocytes is well established phenomenon which poses a lot of questions about myocardial excitability. Current studies of spontaneous Ca-activity in cardiac cells mainly relate to the kinetic characteristics, classification and simulation of Ca-events through ryanodine receptor (RyR) activity modeling. Here, for the first time we pay attention to the Ca-transients having stationary kinetics for correct estimation of the sarcoplasmic reticulum Ca transport.

Upregulation of α2-adrenoceptor synthesis in SHR cardiomyocytes: Recompense without sense - Increased amounts, impaired commands.

Aims: to investigate α2-AR subtype distribution and the relationship between receptor amounts and their functionality in normotensive and spontaneously hypertensive rats.

Methods: experiments were performed on left ventricular cardiomyocytes isolated from Wistar rats and SHR (2-2.5 months).

Disturbance of I-imidazoline receptor signal transduction in cardiomyocytes of Spontaneously Hypertensive Rats.

Imidazoline receptor of the first type (IR) in addition to the established inhibition of sympathetic neurons may mediate the direct control of myocellular functions. Earlier, we revealed that I-mediated signaling in the normotensive rat cardiomyocytes suppresses the nitric oxide production by endothelial NO synthase, impairs sarco(endo)plasmic reticulum Ca-ATPase (SERCA) activity, and elevates intracellular calcium in the cytosol. Also, I-agonists counteract β-adrenoceptor stimulation effects in respect to voltage-gated calcium currents.

[Non-Central Influences of α2-Adrenergic and Imidazoline Agonist Interactions in Isolated ardiomyocytes Cardiac Cells].

Aim: to investigate the functional interaction of α2-adrenergic and imidazoline receptors recently identified on the sarcolemma of isolated cardiomyocytes for regulation of the intracellular calcium and the production of the signal molecule of nitric oxide (NO).

Materials And Methods: experiments were performed on isolated left ventricular cardiomyocytes of Wistar rats. Potential-dependent Ca2+-currents were measured from the whole-cell by the patch-clamp method in "perforated-patch" configuration.

α2-Adrenoceptor signaling in cardiomyocytes of spontaneously hypertensive rats starts to impair already at early age.

α2-Adrenoceptors (α2-AR) found in the cardiomyocyte's sarcolemma represent a very important negative feedback for control of myocardial contractility by endogenous catecholamines. Earlier, we showed that the endogenous neurotransmitter agmatine in micromolar concentrations via α2-AR activates the nitric oxide (NO) synthesis, enhancing the Ca pumping into sarcoplasmic reticulum (SR). In the millimolar doses it inhibits Ca sequestration by SR Ca ATPase (SERCA), acting through the first type of imidazoline receptors.

Synergism of myocardial β-adrenoceptor blockade and I-imidazoline receptor-driven signaling: Kinase-phosphatase switching.

Recently identified imidazoline receptors of the first type (IRs) on the cardiomyocyte's sarcolemma open a new field in calcium signaling research. In particular, it is interesting to investigate their functional interaction with other well-known systems, such as β-adrenergic receptors. Here we investigated the effects of IRs activation on L-type voltage-gated Ca-currents under catecholaminergic stress induced by the application of β-agonist, isoproterenol.

Store-operated Ca2+ entry supports contractile function in hearts of hibernators.

Hibernators have a distinctive ability to adapt to seasonal changes of body temperature in a range between 37°C and near freezing, exhibiting, among other features, a unique reversibility of cardiac contractility. The adaptation of myocardial contractility in hibernation state relies on alterations of excitation contraction coupling, which becomes less-dependent from extracellular Ca2+ entry and is predominantly controlled by Ca2+ release from sarcoplasmic reticulum, replenished by the Ca2+-ATPase (SERCA). We found that the specific SERCA inhibitor cyclopiazonic acid (CPA), in contrast to its effect in papillary muscles (PM) from rat hearts, did not reduce but rather potentiated contractility of PM from hibernating ground squirrels (GS).

Sarcolemmal α2-adrenoceptors control protective cardiomyocyte-delimited sympathoadrenal response.

Sustained cardiac adrenergic stimulation has been implicated in the development of heart failure and ventricular dysrhythmia. Conventionally, α2 adrenoceptors (α2-AR) have been assigned to a sympathetic short-loop feedback aimed at attenuating catecholamine release. We have recently revealed the expression of α2-AR in the sarcolemma of cardiomyocytes and identified the ability of α2-AR signaling to suppress spontaneous Ca transients through nitric oxide (NO) dependent pathways.

Cardioprotective Effect of Modified Peroxiredoxins in Retrograde Perfusion of Isolated Rat Heart under Conditions of Oxidative Stress.

Antioxidant properties of recombinant peroxiredoxin-6 and chimeric protein PSH combining peroxidase and superoxide dismutase activities were studied on the model of retrograde perfusion of isolated rat heart under conditions of H2O2-induced oxidative stress. The exogenous antioxidant proteins exhibited cardioprotective properties manifested in heart rate normalization, maintenance of contractile activity of the myocardium, and prevention of H2O2-induced LPO in oxidative stress. Localization of peroxiredoxin-6 and PSH in the cardiac tissue was determined and myocardial structures most effectively protected by the antioxidant enzymes from ischemia/reperfusion-induced damages were identified.

Alpha-2 adrenoceptors and imidazoline receptors in cardiomyocytes mediate counterbalancing effect of agmatine on NO synthesis and intracellular calcium handling.

Evidence suggests that intracellular Ca(2+) levels and contractility of cardiomyocytes can be modulated by targeting receptors other than already identified adrenergic or non-adrenergic sarcolemmal receptors. This study uncovers the presence in myocardial cells of adrenergic α2 (α2-AR) and imidazoline I1 (I1R) receptors. In isolated left ventricular myocytes generating stationary spontaneous Ca(2+) transients in the absence of triggered action potentials, the prototypic agonist of both receptors agmatine can activate corresponding signaling cascades with opposing outcomes on nitric oxide (NO) synthesis and intracellular Ca(2+) handling.

Analysis of the modal hypothesis of Ca2+-dependent inactivation of L-type Ca2+ channels.

A kinetic model of Ca2+-dependent inactivation (CDI) of L-type Ca2+ channels was developed. The model is based on the hypothesis that postulates the existence of four short-lived modes with lifetimes of a few hundreds of milliseconds. Our findings suggest that the transitions between the modes is primarily determined by the binding of Ca2+ to two intracellular allosteric sites located in different motifs of the CI region, which have greatly differing binding rates for Ca2+ (different k(on)).

Neuropeptide modulation of evoked responses of neurons in the medial septal region of hibernating ground squirrels in conditions of chronic isolation of the medial septal region from preoptic-hypothalamic structures.

Septal slices from hibernating ground squirrels were initially (for two weeks) subjected to basal separation of the septal region and were then used for studies of the effects of neuropeptides extracted from the brains of hibernating animals (TSKYR, TSKY, and DY) and monoaminergic neurotransmitters (noradrenaline and serotonin) on neuronal responses evoked by intraseptal electrical stimulation. Despite removal of a large complex of afferent connections and direct contacts with the preoptic region, the neurons retained their normal reactivity and the normal distribution of response types. Neuropeptides efficiently modulated responses, and had strong facilitatory effects on oligosynaptic short-latency responses consisting of single spikes.

The paradoxically high reactivity of septal neurons in hibernating ground squirrels to endogenous neuropeptides is lost after chronic deafferentation of the septum from the preopticohypothalamic areas.

The effect of neuropeptides (TSKYR, TSKY and DY) and neurotransmitters (serotonin and noradrenaline) on the activity of medial septum (MS) neurons from the brain of summer wakening ground squirrels (WGS), hibernating ground squirrels (HGS), and hibernating ground squirrels with the undercut septum (UHGS) was studied. It was shown that in HGS, the neuropeptides were substantially more effective in modulating the spontaneous activity of MS neurons than in WGS. The undercutting of MS led to the disappearance of the increased responsiveness to the neuropeptides: in UHGS, neuropeptide-induced changes in the spontaneous activity became nearly identical to those in WGS.

The effects of afferent stimulation on neurons in slices of the medial septal area and their modulation by biologically active substances in hibernating and awake ground squirrels.

Evoked neuron activity in slices of the medial septal area and its modulation by neuropeptides and monoamines was studied in two groups of ground squirrels--hibernating and awake animals. Electrical stimulation of the medial forebrain bundle evoked predominantly inhibitory effects of different durations. In addition, responses were seen consisting of resetting of the phase of background volleys to the stimulus after initial inhibition: there were also small numbers of short-latency single-spike responses.

Effect of avermectins on Ca2+-dependent Cl- currents in plasmalemma of Chara corallina cells.

A natural complex of avermectins, aversectin C, and a component of this complex, avermectin A1, were shown to change the conductivity of Ca2+-dependent Cl- channels of plasmalemma of Chara corallina cells by acting from the outer side of the cellular membrane. Low concentrations of aversectin C and avermectin A1 increased the Cl- current: K1/2 = 35 ng/ml for the whole complex and K1/2 = 21 pg/ml for A1. Relatively high concentrations of the compounds suppressed the Cl- current: K1/2 = 2.

The regulation of L-type Ca2+ currents in rat cardiac myocytes.

The regulation of L-type Ca2+ current in isolated rat cardiac cells was studied using the perforated patch-clamp technique. A dual effect of the cAMP-dependent phosphorylation activator, isoproterenol, at different holding potentials (V(h)) was shown. The currents increased at V(h) = -50 mV and decreased at V(h) = -30 mV.

Selective cytostatic and neurotoxic effects of avermectins and activation of the GABAalpha receptors.

A natural avermectin complex, aversectin C, was shown to be capable of exerting selective cytostatic and neurotoxic effects on mammalian cells. Specifically, it killed proliferating neuroblastoma B103 cells but was non-toxic for differentiated cells of this culture. The antiproliferation action of aversectin C was not inhibited by bicuculline or picrotoxin, antagonists of the GABAalpha receptors, and was partly due to the action of avermectin A1, a component of aversectin C.

State-dependent effects of some neuropeptides and neurotransmitters on neuronal activity of the medial septal area in brain slices of the ground squirrel, Citellus undulatus.

Neuronal activity of the medial septal area was recorded extracellularly in brain slices taken from hibernating (winter) and waking (summer) ground squirrels. The effects of neuropeptides identified in the brain tissue of hibernators (Thr-Ser-Lys-Tyr, Thr-Ser-Lys-Tyr-Arg and Asp-Tyr) on the background activity and responses to electrical stimulation of the median forebrain bundle were analysed. For comparison, the effects of bath application of noradrenaline and serotonin were also tested.

Analysis of ectatomin action on cell membranes.

Ectatomin (m = 7928 Da) is a toxic component from the Ectatomma tuberculatum ant venom containing two homologous polypeptide chains (37 and 34 residues) linked to each other by a disulfide bond. In aqueous solution it forms a four alpha-helix bundle. At concentrations of 0.

The effect of some peptides from the hibernating brain on Ca2+ current in cardiac cells and on the activity of septal neurons.

The effects of the peptides TSKYR and DY isolated from the brain of hibernating ground squirrels on Ca2+ current were studied. TSKYR activated Ca2+ current in frog auricle fibers and in single cells from frog ventricle whereas DY blocked Ca2+ current in both preparations. In isolated rat and ground squirrel cardiocytes, TSKYR had no effect on Ca2+ current, and DY increased it.

The kinetic characteristics of L-type calcium channels in cardiac cells of hibernators. 2. Analysis of the kinetic model.

The present paper describes the experimental and theoretical investigations of the kinetic characteristics of the L-type Ca2+ channels in ground squirrels Citellus undulatus in two different physiological states (hibernation and spontaneous arousal). The perforated patch-clamp method was used in the experiments. We have shown in the previous study [1] that Ca2+ currents in hibernating and active animals may be described by the d2f1(2)f2 model.