Effects of adaptation to stress exposure and periodic hypoxia on bioelectric activity of cardiomyocytes of isolated heart in ischemia and reperfusion]

Action potential (AP) of cardiomyocytes was recorded in experiments on isolated perfused according to Langendorf rat hearts. The effect was estimated of preliminary adaptation to intermittent hypobaric hypoxia or to repeated short-term stress exposure on the resting potential (RP) and the amplitude and duration of action potential (APD) in global ischemia and reperfusion. It was shown that adaptation to hypoxia is more effective in prevention of ischemic fall of RP, AP and APD. In reperfusion, the parameters enumerated restored more quickly and efficiently in hearts from adapted to stress animals.     

The influence of glutamic and aminoacetic acids on the excitability of the liverwort Conocephalum conicum

Intracellular microelectrode measurements revealed that a resting potential (RP), an action potential (AP) and a calcium component of AP (named voltage transient, VT) can be influenced by glutamic acid (Glu) and aminoacetic acid (glycine, Gly) in the liverwort Conocephalum conicum. In the continuous presence of 5mM Glu or 5mM Gly, the RP hyperpolarized constantly and the plants became desensitized to the excitatory amino acids (Glu or Gly). Under such circumstances, the amplitudes of APs evoked by stimuli other than Glu or Gly grew, as did their calcium components (VTs). The sudden application of 1-15 mM Glu or Gly to a thallus not yet desensitized resulted in an excitation, i.e. a single AP or AP series. Aspartate (Asp) could not substitute for Glu in any way. Simultaneous action of both amino acids acted synergically to trigger APs. The same phenomenon was observed when glycine solution was enriched with N-methyl-D-aspartic acid (NMDA). Gly-induced APs were totally hindered by 1mM D-amino-5-phosphonopentanoic acid (AP5)--an inhibitor of ionotropic glutamate receptors of the NMDA kind. Glu-induced APs could be totally suppressed by 1mM AP5 as well as by 1mM 6,7-dinitroquinoxaline-2,3-dione (DNQX)--an inhibitor of AMPA/KA receptors. DNQX also completely blocked the calcium component of Glu-evoked APs. After DNQX treatment, the only response to Glu was a membrane potential hyperpolarization (like the Glu response in a desensitized plant). It was concluded that the Glu-induced depolarization and hyperpolarization are separate phenomena. The stimulatory effects of both Glu and Gly on liverwort excitability may be the consequences of an activation of a variety of ionotropic Glu receptor subtypes.     

Comparative assessment of the effect of adaptation to stress exposure and high altitude hypoxia on heart resistance to reperfusion injury after total ischemia]

Experiments on isolated Wistar rat hearts perfused according to Langendorff showed that adaptation to stress exposure limited the depression of contraction amplitude and contracture and possessed an antiarrhythmic effect in reperfusion. Furthermore, adaptation to stress exposure efficiently limited reperfusion damage to sarcolemma. It was shown that adaptation to hypoxia did not result in any increase in the heart resistance to reperfusion damage following total ischemia. Possible mechanisms of differences in the protective effects of adaptation to stress exposure and hypoxia are discussed.     

尼氟灭酸通过钙库钙释放引起豚鼠耳蜗螺旋动脉平滑肌细胞超极化(英文)

本研究旨在观察氯离子通道阻断剂尼氟灭酸（niflumic acid,NFA）引起豚鼠耳蜗螺旋动脉平滑肌细胞产生超极化的机制。以豚鼠为实验动物,运用细胞内微电极和全细胞膜片钳记录技术,观察NFA和其它药物对急性分离的耳蜗螺旋动脉平滑肌细胞的作用。结果显示：NFA、indanyloxyacetic acid94（LAh-94）和diSOdium4,4’-diisothiocyanatostilbene-2,2’-disulfonate（DIDS）可使低静息膜电位的细胞产生超极化,但对高静息膜电位的细胞无明显作用。低静息膜电位细胞的平均静息电位为（-42．47±1．38）mV（n=24）,100μmol／LNFA、10μmol／LIAA-94和200μmol／LDIDS分别使细胞超极化至（13．7±4．3）mV=9,P〈0．01）,（11．4±4．2）mV（n=7,P〈0．01）和（12．3±3．7）mV（n=8,P〈0．01）,这种氯离子通道阻断剂引起细胞超极化反应的效应呈浓度依赖性。NFA引起的超极化和外向电流几乎完全被100nmol／L iberiotoxin、100nmol／L charybdotoxin、10mmol／L tetraethylammonium、50μmol／LBAPTA—AM、10μmol／Lryanodine和0．1-10mmol／Lcaffeine阻断,但不能被100μmol／Lnifedipine、100μmol／LCdCI,和无Ca^2＋灌流外液阻断。结果捉示：氯离_了通道的阻断剂NFA可通过平滑肌细胞内钙库的钙释放增加细胞内钙,进而激活钙依赖的钾通道,产生耳蜗螺旋动脉平滑肌细胞的超极化反应。     

豚鼠冠状动脉微动脉细胞静息膜电位的分布特性及机制

目的:观察冠状动脉微动脉细胞静息膜电位(RP)的分布特性及形成机制.方法:离体豚鼠冠状动脉微动脉(直径小于100 μm)上,应用细胞内微电极技术记录细胞RP.结果:①成功记录到112个细胞,细胞平均RP为(-65±4.2)mV,应用高斯函数拟合后细胞RP呈双峰状分布,两个峰值分别为-43和-74 mV,分别称为高和低R...     

Activation of intestinal smooth muscle cells by interstitial cells of Cajal in simulation studies

Activation of a two-dimensional sheet network (5 parallel chains of 5 cells each) of simulated intestinal smooth muscle cells (SMCs) by one interstitial cell of Cajal (ICC) was modeled by PSpice simulation. The network of 25 cells was not interconnected by gap-junction channels; instead, excitation was transmitted by the electric field that develops in the junctional clefts (JC) when the prejunctional membrane fires an action potential (AP). Transverse propagation between the parallel chains occurs similarly. The ICC cell was connected to cell E5 of the network [5th cell of the 5th (E) chain] via a high-resistance junction. The stimulating current, applied to the ICC cell interior, was made to resemble the endogenous undershooting slow wave (I(SW)). An I(SW) of 2.4 nA (over a rise time of 4 ms) took the ICC cell from a resting potential (RP) of -80 mV to a membrane potential of -41 mV. The slow wave produced a large negative cleft potential in the JC (V(JC); ICC-E5). The V(jc) brought the postjunctional membrane of E5 to threshold, causing this cell to fire an AP. This, in turn, propagated throughout the SMC network. If the ICC cell was given an RP of -55 mV (like SMC) and a slow wave of 40 mV amplitude (I(SW) of 1.8 nA), it still activated the SMC network. This was also true when the ICC cell was made excitable (developing an overshooting, fast-rising AP). In summary, one ICC cell displaying a slow wave was capable of activating a network of SMC in the absence of gap junctions.     

Effect of an anomalous broadening of the synchronization band after electric stimulation of heart tissues

Synchronization effects of the second order induced by a change of the action potential (AP) shape in relation to the frequency of periodic stimulation were studied. Mechanism of anomalous increase of the synchronization band at periodic stimulation of the heart fibers was explained. By means of a modified method of synchronization diagrams the synchronization bands were calculated for possible stimulation regimes taking into account a change in RP shape and dynamic threshold (DT) depending on the frequency of the initiated regimes. Regions of stimulating signals parameters (multiplicity regions or prolonging regions) were discovered, within the range of which the same stimulating signal may induce different synchronization regimes. Physiological meaning of the existence of anomalous synchronization regimes which significantly broaden the adaptation possibilities of the heart is discussed.     

Electrical response to fertilization in ascidian oocytes

The fertilization potential of the ascidian oocyte has been studied using two intracellular electrodes. Two classes of oocyte were observed; low resting potential (RP) oocytes of ?20 to ?35 mV and high RP oocytes of ?80 to ?90 mV. The two types have comparable membrane resistance, falling in the range of 100–300 MΩ, and both may be fertilized and develop normally, although the fertilization potential (FP) is different in the two cases. High RP oocytes give rise to step-like regenerative potentials which attain positive values, whereas low RP oocytes give rise to slower depolarizations that reach zero level. In both cases the FP was sometimes preceded by a small-step depolarization as normally observed in the sea urchin. Irrespective of the original RP, the membrane resistance always decreased to 1–10% of its initial value during the first few minutes of the FP plateau. In contrast when the membrane was depolarized to a comparable potential by current injection the membrane resistance did not decrease. Polyspermic fertilization was induced by removing the extracellular coats, aging the oocytes and using high densities of sperm. The FP in monospermic and polyspermic oocytes were comparable and we could not correlate additional sperm interactions with additional electrical events. Our results suggest that the plasma membrane in ascidian oocytes lacks intrinsic mechanisms, electrical or otherwise, to prevent polyspermic fertilization.     

Cav1.2 calcium channels modulate the spiking pattern of hippocampal pyramidal cells

Ca(v)1.2 L-type calcium channels support hippocampal synaptic plasticity, likely by facilitating dendritic Ca2+ influx evoked by action potentials (AP) back-propagated from the soma. Ca2+ influx into hippocampal neurons during somatic APs is sufficient to activate signalling pathways associated with late phase LTP. Thus, mechanisms controlling AP firing of hippocampal neurons are of major functional relevance. We examined the excitability of CA1 pyramidal cells using somatic current-clamp recordings in brain slices from control type mice and mice with the Ca(v)1.2 gene inactivated in principal hippocampal neurons. Lack of the Ca(v)1.2 protein did not affect either affect basic characteristics, such as resting membrane potential and input resistance, or parameters of single action potentials (AP) induced by 5 ms depolarising current pulses. However, CA1 hippocampal neurons from control and mutant mice differed in their patterns of AP firing during 500 ms depolarising current pulses: threshold voltage for repetitive firing was shifted significantly by about 5 mV to more depolarised potentials in the mutant mice (p<0.01), and the latency until firing of the first AP was prolonged (73.2+/-6.6 ms versus 48.1+/- 7.8 ms in control; p<0.05). CA1 pyramidal cells from the mutant mice also showed a lowered initial spiking frequency within an AP train. In control cells, isradipine had matching effects, while BayK 8644 facilitated spiking. Our data demonstrate that Ca(v)1.2 channels are involved in regulating the intrinsic excitability of CA1 pyramidal neurons. This cellular mechanism may contribute to the known function of Ca(v)1.2 channels in supporting synaptic plasticity and memory.     

The action of ultrasound on the contraction strength and action potential of the papillary muscle of the rat heart

In experiments on isolated rat papillary muscles the effects of therapeutic doses of ultrasound (US) (intensity, less than 2 W/cm2) with frequency of 0.88 MHz on contraction force and action potential (AP) were studied. 12 muscles (from 14) responded to 3-min exposition of the US with a rise both in contraction force and in resting tension. Sensitivity to US and a value of inotropic effect changed significantly between the preparation, and the threshold intensities of US varied from 0.3 to 2 W/cm2. In 3 experiments the inotropic effect of US was more than 100%, but in others it was about 50%. Two preparations were not sensitive to the US. The positive inotropic effect of US was accompanied by membrane depolarization (up to 20 mV) and by prolongation of AP duration measured at 10% of its amplitude (APD10). The correlation between the increase in contraction force and APD10 was demonstrated. Some preparations responded to US with high depolarization (up to 50 mV) and were inexcitable. The US induced an increase in temperature less than 1 degree C, therefore all the effects of US could not be explained as a result of temperature rise.     

The effect of adaptation to stress exposures and to periodic hypoxia on the cardiomyocyte trigger activity of the papillary muscles in the rat]

Action potential of cardiomyocytes was recorded in experiments on isolated papillary muscle of the rat left ventricle. The effect was estimated of preliminary adaptation to intermittent hypobaric hypoxia or to short-term stress exposure on the incidence and the pronouncement of delayed after depolarization and of trigger activity induced by a high frequency stimulation against the background of isoproterenol (10(-8) M). It was shown that adaptation to hypoxia or to stress reduced the incidence of delayed after depolarization and of trigger activity, adaptation to stress exerting a more pronounced effect. Immobilization stress (6 hours) potentiated the trigger activity, adaptation to stress exerting a more pronounced effect. Immobilization stress (6 hours) potentiated the trigger activity and this potentiation was effectively prevented by either type of adaptation.     

Expression of voltage dependent potassium currents in freshly dissociated rat articular chondrocytes.

The electrophysiological properties of voltage dependent potassium channels from freshly dissociated rat articular chondrocytes were studied. The resting membrane potential (-42.7+/-2.0 mV) was significantly depolarized by increasing concentrations of external potassium. No change was observed when external chloride concentration was varied. Addition of TEA, 4AP, alpha-Dendrotoxin and charybdotoxin depolarized resting membrane potential. Whole cell patch clamp studies revealed the presence of outwardly rectifying currents whose kinetic and pharmacological properties suggest the expression of voltage dependent potassium channels. Two kinds of currents were observed under the same experimental conditions. The first one, most frequently observed (80%), starts activating near -50 mV, with V(1/2)=-18 mV, G(max)=0.30 pS/pF. The second kind was observed in only 10% of cases; It activates near -40 mV, with(1/2)=+28.35 mV, G(max)=0.28 pS/pF pA/pF and does not inactivates. Inactivating currents were significantly inhibited by TEA (IC(50)=1.45 mM), 4AP (IC(50)=0.64 mM), CTX (IC(50) = 10 nM), alpha-Dendrotoxin (IC(50) < 100 nM) and Margatoxin (IC(50)=28.5 nM). These results show that rat chondrocytes express voltage dependent potassium currents and suggest a role of voltage-dependent potassium channels in regulating membrane potential of rat chondrocytes.     

Adaptation of the body to stressors prevents the cardiotoxic effect of rifampicin but not polymyxin B]

It was established on isolated rat hearts that adaptation of the organism to stress exposure effectively limits toxic effect of chronic rifampicin administration (7 mg/kg/day for 8 days) and does not affect the depression of contractile function induced by chronic polymyxin B administration (0.12 mg/kg/day for 8 days). Possible mechanism of the effect of organism's adaptation to stress on the resistance of heart to antibiotics is under discussion.     

Adrenomedullin influences dissociated rat area postrema neurons

The area postrema (AP) is one of a specialized group of central nervous system (CNS) structures devoid of a significant blood-brain barrier (BBB), collectively known as the circumventricular organs (CVO). While peptides are normally excluded from access to most regions of the CNS, the AP contains neurons with a high density of receptors for many circulating peptides, very likely including those for adrenomedullin (AM). In this study, whole-cell patch-clamp recordings were obtained from 114 dissociated rat AP neurons. The mean resting membrane potential (RMP) of these neurons (n=79) was -54.3+/-0.8 mV, the mean input resistance (IR) was 3.1+/-0.2 GOmega and the spike amplitude of neurons included in this study was always greater than 90 mV. Current-clamp studies showed that bath application of AM depolarized 39.2% (31 of 79) and hyperpolarized 45.6% (36 of 79) of neurons tested. Both effects were found to be concentration dependent from 10(-12) to 10(-7) M. These data support the idea that specific populations of CNS neurons within the AP are directly influenced by AM and support the concept that AM may act at AP to influence central autonomic control. We also examined the roles of specific ion channels in regulating the AM-induced excitability of AP neurons through voltage-clamp studies. These experiments suggest potential actions of AM in modulating voltage gated calcium channels, effects which have the additional consequence of inhibiting calcium activated potassium conductances (I(K(Ca))). These data demonstrate direct effects of AM on dissociated AP neurons and identify ion channels, the modulation of which, may underlie these effects.     

The resting membrane potential of Drosophila melanogaster larval muscle depends strongly on external calcium concentration

The resting membrane potential (RMP) of most cells is not greatly influenced by the transmembrane calcium gradient because at rest, the membrane has very low permeability to calcium. We have observed, however, that the resting membrane potential of muscle cells in the larval bodywall of Drosophila melanogaster varies widely as the external calcium concentration is modified. The RMP depolarized as much as 21.8 mV/mM calcium at low concentrations, and on average, about 10 mV/mM across a range typical of neurophysiological investigations. The extent to which muscle RMP varies has important implications for the measurement of synaptic potentials as well. Two parameters of excitatory junctional potential (EJP) voltage were compared across a range of RMPs. EJP amplitude (ΔV) and peak voltage (maxima) change as a function of RMP; on average, a 10 mV change in RMP elicits a 4-5 mV change in EJP amplitude and peak voltage. The influence of the calcium gradient on resting and synaptic membrane potentials led us to investigate the endogenous ion concentrations of larval hemolymph. In addition to the major monovalent ions and calcium, we report the first voltammetric analysis of magnesium concentration in larval fruit fly hemolymph.     

The effect of diazepam on potassium contractures, contraction threshold, and resting tension in rat skeletal muscles

The effects of diazepam on potassium contractures, contraction threshold, and resting tension have been examined in rat soleus muscle fibres. Two actions of the drug were defined that could not be attributed to changes in the resting membrane potential or depolarization in high potassium solutions. The major effect was an increase in the amplitude of submaximal tension during either twitches or potassium contractures and an increase in resting tension. At 400 microM diazepam, there was (a) a fourfold increase in 40 mM potassium contracture tension, (b) a negative shift of 8 mV in the membrane potential for half maximum tension estimated from the best fit of a Boltzmann-type equation to average potassium contracture data, (c) a negative shift of 8 mV in the threshold for contraction measured under voltage clamp conditions, and (d) a contracture of variable amplitude to a level that was occasionally equivalent to maximum tetanic tension. These potentiating actions of diazepam depended on drug concentration within the range of 100-800 microM. In contrast, the second effect of diazepam, depression of maximum tension by 10-15%, was independent of drug concentration between 100 and 400 microM. The results support the idea that diazepam produces an increase in resting myoplasmic calcium concentrations.     

Effect of preliminary adaptation to short-term stress exposure on the resistance of the spontaneously contracting myocardium to a lipid peroxidation inducer

Contractile function of the isolated right atrium was studied in male Wistar rats adapted to short-term stressor exposures at varying times after adaptation was completed. Adaptation to short-term stressor exposures induced a limited decrease in myocardial contractility immediately after adaptation was over. On the 3d day an additional reduction in the characteristics of contractile function was still observed. However, by the 5th day the characteristics recovered to the control level. At the same time adaptation completely prevented the derangement of myocardial contractility, induced by exposure to a prolonged stress. That protective effect was observed as early as adaptation was completed, on days 3 and 5 after adaptation, and became lessened on the 10th day. It is assumed that on the 5th day after adaptation the animals are in a postadaptation state where the untoward effect of adaptation disappears whereas the protective effect is demonstrable to a full extent. As a result all the characteristics of myocardial contractility following a prolonged stress on the 5th day after completion of short-term stressor exposures differed in no way from the control parameters.     

Millimeter Wave Radiation Activates Leech Nociceptors via TRPV1-Like Receptor Sensitization

There is evidence that millimeter waves (MMWs) can have an impact on cellular function, including neurons. Earlier in vitro studies have shown that exposure levels well below the recommended safe limit of 1 mW/cm² cause changes in the action potential (AP) firing rate, resting potential, and AP pulse shape of sensory neurons in leech preparations as well as alter neuronal properties in rat cortical brain slices; these effects differ from changes induced by direct heating. In this article, we compare the responses of thermosensitive primary nociceptors of the medicinal leech under thermal heating and MMW irradiation (80–170 mW/cm² at 60 GHz). The results show that MMW exposure causes an almost twofold decrease in the threshold for activation of the AP compared with thermal heating (3.9 ± 0.4 vs. 8.3 ± 0.4 mV, respectively). Our analysis suggests that MMWs-mediated threshold alterations are not caused by the enhancement of voltage-gated sodium and potassium conductance. We propose that the reduction in AP threshold can be attributed to the sensitization of the transient receptor potential vanilloid 1-like receptor in the leech nociceptor. In silico modeling supported our experimental findings. Our results provide evidence that MMW exposure stimulates specific receptor responses that differ from direct thermal heating, fostering the need for additional studies.     

Effects of electroporation on optically recorded transmembrane potential responses to high-intensity electrical shocks

The outcome of defibrillation shocks is determined by the nonlinear transmembrane potential (DeltaVm) response induced by a strong external electrical field in cardiac cells. We investigated the contribution of electroporation to DeltaVm transients during high-intensity shocks using optical mapping. Rectangular and ramp stimuli (10-20 ms) of different polarities and intensities were applied to the rabbit heart epicardium during the plateau phase of the action potential (AP). DeltaVm were optically recorded under a custom 6-mm-diameter electrode using a voltage-sensitive dye. A gradual increase of cathodal and well as anodal stimulus strength was associated with 1) saturation and subsequent reduction of DeltaVm; 2) postshock diastolic resting potential (RP) elevation; and 3) postshock AP amplitude (APA) reduction. Weak stimuli induced a monotonic DeltaVm response and did not affect the RP level. Strong shocks produced a nonmonotonic DeltaVm response and caused RP elevation and a reduction of postshock APA. The maximum positive and maximum negative DeltaVm were recorded at 170 +/- 20 mA/cm2 for cathodal stimuli and at 240 +/- 30 mA/cm2 for anodal stimuli, respectively (means +/- SE, n = 8, P = 0.003). RP elevation reached 10% of APA at a stimulus strength of 320 +/- 40 mA/cm2 for both polarities. Strong ramp stimuli (20 ms, 600 mA/cm2) induced a nonmonotonic DeltaVm response, reaching the same largest positive and negative values as for rectangular shocks. The transition from monotonic to nonmonotonic morphology correlates with RP elevation and APA reduction, which is consistent with cell membrane electroporation. Strong shocks resulted in propidium iodide uptake, suggesting sarcolemma electroporation. In conclusion, electroporation is a likely explanation of the saturation and nonmonotonic nature of cellular responses reported for strong electric stimuli.