Role of membrane potential in vasomotion of isolated pressurized rat arteries

Vasomotion, the phenomenon of vessel diameter oscillation, regulates blood flow and resistance. The main parameters implicated in vasomotion are particularly the membrane potential and the cytosolic free calcium in smooth muscle cells. In this study, these parameters were measured in rat perfused-pressurized mesenteric artery segments. The application of norepinephrine (NE) caused rhythmic diameter contractions and membrane potential oscillations (amplitude; 5.3 +/- 0.3 mV, frequency; 0.09 +/- 0.01 Hz). Verapamil (1 microM) abolished this vasomotion. During vasomotion, 10(-5) M ouabain (Na(+)-K(+) ATPase inhibitor) decreased the amplitude of the electrical oscillations but not their frequency (amplitude; 3.7 +/- 0.3 mV, frequency; 0.08 +/- 0.002 Hz). Although a high concentration of ouabain (10(-3) M) (which exhibits non-specific effects) abolished both electrical membrane potential oscillations and vasomotion, we conclude that the Na+-K+ ATPase could not be implicated in the generation of the membrane potential oscillations. We conclude that in rat perfused-pressurized mesenteric artery, the slow wave membrane type of potential oscillation by rhythmically gating voltage-dependent calcium channels, is responsible for the oscillation of intracellular calcium and thus vasomotion.     

Oscillation of the electric potential of frog skin under the effect of Li+: Experimental approach

Summary When a frog skin is used to separate two compartments, and lithium is added to the external medium, transmembrane electric potential oscillations frequently occur. When no external current is imposed, sustained oscillations, with a period of about 10 min, are maintained for several hours. An oscillation of the Na⁺ influx accompanies the electric oscillation, though the two oscillations are out of phase to a greater or less extent.Theophyllin promotes a significant decrease in the mean electric potential of the skin, but it does not affect very much the characteristics of the oscillation. Important factors influencing the oscillation are temperature, permeability of the external membrane to lithium, and potassium concentration in the internal medium. No correlation can be detected between oscilation characteristics and skin area. This suggests that the oscillation is of a local nature, possibly originating at the cellular level. Occurrence of macroscopic oscillations implies coupling between local oscillators. Coupling between two epithelia has been studied under diverse conditions. The coupling is of an electrical nature: by varying the value of the coupling resistance, it is possible to control synchronization of the oscillations.     

A model for self-sustained potential oscillation of lipid bilayer membranes induced by the gel-liquid crystal phase transitions.

To clarify the mechanism of self-sustained oscillation of the electric potential between the two solutions divided by a lipid bilayer membrane, a microscopic model of the membrane system is presented. It is assumed, on the basis of the observed results (Yoshikawa, K., T. Omachi, T. Ishii, Y. Kuroda, and K. liyama. 1985. Biochem. Biophys. Res. Commun. 133:740-744; Ishii, T., Y. Kuroda, T. Omochi, and K. Yoshikawa. 1986. Langmuir. 2:319-321; Toko, K., N. Nagashima, S. liyama, K. Yamafuji, and T. Kunitake. Chem. Lett. 1986:1375-1378), that the gel-liquid crystal phase transition of the membrane drives the potential oscillation. It is studied, by using the model, how and under what condition the repetitive phase transition may occur and induce the potential oscillation. The transitions are driven by the repetitive adsorption and desorption of proton by the membrane surface, actions that are induced the periodic reversal of the direction of protonic current. The essential conditions for the periodic reversal are (a) at least one kind of cations such as Na+ or K+ are included in the system except for proton, and the variation of their permeability across the membrane due to the phase transition is noticeably larger than that of proton permeability; and (b) the phase transition has a hysteresis. When these conditions are fulfilled, the self-sustained potential oscillation may be brought about by adjusting temperature, pH, and the cation concentration in the solutions on both sides of the membrane. Application of electric current across the membrane also induces or modifies the potential oscillation. Periodic, quasiperiodic, and chaotic oscillations appear especially, depending on the value of frequency of the applied alternating current.     

Group-theory classification of oscillations of plasma clusters

Normal oscillations of three-dimensional configurations of dust grains trapped in a spherically symmetric potential well are studied. All possible oscillations of a system consisting of 7–13 grains are classified in terms of group theory. For a Coulomb interaction potential, all the oscillation frequencies are calculated. The frequencies and polarizations of some oscillation modes are obtained for an arbitrary interaction potential.     

The fertilization potential and associated membrane potential oscillations during the resumption of meiosis in the egg of the ascidian Phallusia mammillata.

The fertilization potential in Phallusia mammillata consisted of an initial rapid depolarization. This initial sperm-triggered depolarization was followed by a phase of membrane depolarization which was of either long or short duration, depending on the eggs. When of long duration, the phase of membrane depolarization was divided into two periods: the first one began with a plateau (Em = +20.2 +/- 1.1 mV; duration = 1.7 +/- 0.14 min) which was followed by a series of membrane potential oscillations (n = 3.1 +/- 0.25) lasting 2.4 +/- 0.2 min. The second period also began as a plateau (Em = approximately 0 mV; duration = 3.40 +/- 0.20 min) which was followed by a series of oscillations (n = 11.5 +/- 0.5) lasting 11.8 +/- 0.6 min, followed by a membrane repolarization. The second series of oscillations often continued rising from the resting potential value. In the eggs displaying a short duration of membrane depolarization, the second period of depolarization was shortened (lasting only 3.5 +/- 0.5 min) since it lacked the second plateau. In addition it displayed a smaller number of oscillations (n = 4.7 +/- 0.6). As a consequence of this shortening, the membrane repolarized sooner. After repolarization, the membrane displayed several potential oscillations that started from the repolarization level. Regardless of the length of the depolarized plateau phases, the total number of membrane oscillations and the time period during which they occurred were constant. Eggs displaying a long depolarization phase had 15.9 +/- 0.6 oscillations in a 19.5 +/- 0.6 min interval, while eggs having a short depolarization phase had 16.0 +/- 0.8 oscillations in a 18.1 +/- 0.3 min interval. The time period during which the potential oscillations occurred corresponded remarkably well with the time of the meiotic divisions: the formation of the first polar body was detected about 80 sec after the end of the first series of oscillations; the second polar body was extruded about 85 sec after the last membrane oscillation occurred.     

On the mechanism of nitrobenzene liquid membrane oscillators containing hexadecyltrimethylammonium bromide

The oscillatory behaviour of a liquid membrane oscillator was investigated in order to contribute to the oscillation mechanism at the molecular level. The chosen system involved nitrobenzene as liquid membrane containing a constant amount of picric acid. The aqueous donor phase contained the cationic surfactant, hexadecyltrimethylammonium bromide, and ethanol. The aqueous acceptor phase was made up by sucrose solution. It was established that the oscillations take place exclusively at the aqueous acceptor phase/membrane interface. Three stages mechanism of the oscillation (I--induction period, II--first peak formation, III--creation of the first peak) together with appropriate processes were proposed. The molecular events provoking the oscillations of electric potential difference between the two aqueous phases concern: 1) the diffusion of hexadecyltrimethylammonium bromide and ion pairs formed by cation of the surfactant and the picrate anion to the vicinity of the membrane/acceptor phase interface, 2) sudden adsorption of these ion-pairs at this interface in non-catalytic and autocatalytic steps, 3) desorption of ion pairs from the a/m interface to the acceptor phase. It is shown by numerical simulations that the proposed mechanism may account for the observed oscillations and for the species distribution throughout the system as found experimentally.     

A three-species model explaining cyclic dominance of Pacific salmon

The four-year oscillations of the number of spawning sockeye salmon (Oncorhynchus nerka) that return to their native stream within the Fraser River basin in Canada are a striking example of population oscillations. The period of the oscillation corresponds to the dominant generation time of these fish. Various—not fully convincing—explanations for these oscillations have been proposed, including stochastic influences, depensatory fishing, or genetic effects. Here, we show that the oscillations can be explained as an attractor of the population dynamics, resulting from a strong resonance near a Neimark Sacker bifurcation. This explains not only the long-term persistence of these oscillations, but also reproduces correctly the empirical sequence of salmon abundance within one period of the oscillations. Furthermore, it explains the observation that these oscillations occur only in sockeye stocks originating from large oligotrophic lakes, and that they are usually not observed in salmon species that have a longer generation time.     

Oxytocin-induced Ca2+ responses in human myometrial cells

Complex spatiotemporal changes in intracellular Ca2+ were monitored in an immortalized human myometrial cell line (PHM1-41) and first-passage human myometrial cells after oxytocin stimulation (1. 0-1000 nM). Laser cytometry revealed intracellular Ca2+ oscillations in both culture systems starting at 1.0 nM, which were followed by repetitive Ca2+ transients by 10-15 min that lasted for at least 90 min. The amplitude of the initial Ca2+ spike was dose dependent, while the frequency of Ca2+ oscillations identified by Fast Fourier Transform (FFT) tended to increase with dose. Removal of oxytocin resulted in termination of oscillations. Analysis of the sources of the Ca2+ involved in oscillations indicated that the major contribution to oscillation frequencies of 相似文献   

Membrane Potential Oscillations Produced by Excitatory Amino Acids in Isolated Spinal Neurons of the Lamprey Lampetra fluviatilis

Membrane potential (MP) oscillations produced by excitatory amino acids (EAA) have been studied in branching neurons isolated by an enzymatic-mechanical method from the lamprey spinal cord. It was shown that (1) all studied EAA (glutamate, kainate, NMDA, aspartate, and quisqualate) evoke an ion current and a short-term reversible depolarization in studied cells; (2) EAA added to perfusion solution may produce MP oscillations, with kinetic parameters and duration of the oscillation depending on the amino acid used (the most effective are kainate and NMDA, the least effective, quisqualate); (3) oscillations can be irregular (of the type of a synaptic noise or of a long-term plateau of depolarization with action potentials—AP) or regular, with frequency of 0.5–1.5 Hz. Amplitude of both oscillation types depends on MP level, frequency is more steady for each cell and less depends on MP. In 68 out of 128 studied cells, oscillations could be evoked, which indicates that a significant part of lamprey spinal neurons have intrinsic capability for MP oscillations and probably pacemaker properties. The functional role of oscillations can be different. They can take cells out from the profound inhibition state, synchronize activity of rhythm generation neurons and/or be the base for trigger signals (AP firing) sent by locomotor neuronal circuits to trunk muscles.     

Concentration dependence of the veratrine effect on inducing depolarization and membrane potential oscillation in skeletal muscle.

The concentration dependence of the effect of veratrine in inducing depolarization and membrane potential oscillation in the frog sartorius muscle has been studied. (1) On increasing the veratrine concentration from 0.025 to 1 mM, the latency period of the development of membrane potential oscillation and depolarization is proportionally shortened. (2) On changing the veratrine concentration from 0.025 to 1 mM, the magnitude of depolarization is raised logarithmically. (3) When the veratrine concentration reaches 0.05-0.1 mM, both the amplitude and the frequency of the membrane potential oscillation increase. On rising to 1 mM, a further increase in frequency to eight-fold occurs especially in the later phase of oscillation. At this concentration range, the amplitude of oscillation inversely proportional to the concentration of veratrine. (4) On increasing the veratrine concentration above 0.1 mM, the membrane potential oscillation ceases after a temporary rise of frequency. This inhibitory effect of veratrine is, however, reversible, and oscillations appear again, despite the absence of veratrine in Ringer's solution. This also proves the persistance of the veratrine effect.     

Mitochondrial metabolism reveals a functional architecture in intact islets of Langerhans from normal and diabetic Psammomys obesus

The cells within the intact islet of Langerhans function as a metabolic syncytium, secreting insulin in a coordinated and oscillatory manner in response to external fuel. With increased glucose, the oscillatory amplitude is enhanced, leading to the hypothesis that cells within the islet are secreting with greater synchronization. Consequently, non-insulin-dependent diabetes mellitus (NIDDM; type 2 diabetes)-induced irregularities in insulin secretion oscillations may be attributed to decreased intercellular coordination. The purpose of the present study was to determine whether the degree of metabolic coordination within the intact islet was enhanced by increased glucose and compromised by NIDDM. Experiments were performed with isolated islets from normal and diabetic Psammomys obesus. Using confocal microscopy and the mitochondrial potentiometric dye rhodamine 123, we measured mitochondrial membrane potential oscillations in individual cells within intact islets. When mitochondrial membrane potential was averaged from all the cells in a single islet, the resultant waveform demonstrated clear sinusoidal oscillations. Cells within islets were heterogeneous in terms of cellular synchronicity (similarity in phase and period), sinusoidal regularity, and frequency of oscillation. Cells within normal islets oscillated with greater synchronicity compared with cells within diabetic islets. The range of oscillatory frequencies was unchanged by glucose or diabetes. Cells within diabetic (but not normal) islets increased oscillatory regularity in response to glucose. These data support the hypothesis that glucose enhances metabolic coupling in normal islets and that the dampening of oscillatory insulin secretion in NIDDM may result from disrupted metabolic coupling.     

High-frequency oscillations and circadian rhythm of the membrane potential in Spinach leaves

The microelectrode technique was used to follow oscillations in membrane potential in mesophyll cells of spinach (Spinacia oleracea L.) during exposure do different photoperiodic conditions. Both high-frequency oscillations and circadian variations were observed. The circadian rhythm was imposed on the period of high-frequency oscillation during short days as well as in continuous light: The free-running period was 25.2 h. The average period of high-frequency oscillation increased from 7.64 min in the dark to 19.95 min in the light within several minutes after dark to light transition. This period length coincides with the established period length for oscillations in the redox potential in the chloroplast suspensions of spinach.Abbreviations CL continuous light - SD short day - MP membrane potential     

Computational theories on the function of theta oscillations

Neural rhythms can be studied in terms of conditions for their generation, or in terms of their functional significance. The theta oscillation is a particularly prominent rhythm, reported to be present in many brain areas, and related to many important cognitive processes. The generating mechanisms of theta have extensively been studied and reviewed elsewhere; here we discuss ideas that have accumulated over the past decades on the computational roles it may subserve. Theories propose different aspects of theta oscillations as being relevant for their cognitive functions: limit cycle oscillations in neuronal firing rates, subthreshold membrane potential oscillations, periodic modulation of synaptic transmission and plasticity, and phase precession of hippocampal place cells. The relevant experimental data is briefly summarized in the light of these theories. Specific models proposing a function for theta in pattern recognition, memory, sequence learning and navigation are reviewed critically. Difficulties with testing and comparing alternative models are discussed, along with potentially important future research directions in the field.     

On the nature of global plasma oscillations in a tokamak. Part II: Spatial structure and propagation of perturbations observed at the T-10 tokamak

Large-scale plasma oscillations (so-called MHD oscillations) observed at the T-10 tokamak are investigated. The central electron cyclotron heating was used to enhance oscillations at the m/n = 1/1 mode with the goal of determining the internal characteristics of the process. The spatially resolved electron cyclotron emission diagnostics allowed analyzing the propagation characteristics of plasma perturbations. The experiments have revealed that excitation of oscillations in a particular mode occur simultaneously in the entire area located within the corresponding rational magnetic surface. The propagation of plasma perturbations along the torus is found to be inhomogeneous. The electron cyclotron emission diagnostics allowed finding eigen (resonance) frequencies of plasma oscillations from the parameters of their inhomogeneous propagation in the plasma core and comparing them with spectra of oscillations of the magnetic field induced by the plasma current in the edge plasma, which were recorded by magnetic probes. It is established that the frequencies of eigenmodes are independent of the electron temperature, plasma density, and auxiliary heating power. Even spatial harmonics of the principal magnetic surface are observed under strong excitation of oscillations. The rational magnetic surfaces that determine oscillation harmonics retain their position during the entire steady-state phase of the total plasma current in spite of the strong sharpening of the temperature profile due to central heating.     

A model of intracellular Ca2+ oscillations based on the activity of the intermediate-conductance Ca2+-activated K+ channels

Intracellular Ca2+ oscillations are observed in a large number of non-excitable cells. While most appear to reflect an intermittent Ca2+ release from intracellular stores, in some instances intracellular Ca2+ oscillations strongly depend on Ca2+ influx, and are coupled to oscillations of the membrane potential, suggesting that a plasma membrane-based mechanism may be involved. We have developed a theoretical model for the latter type of intracellular Ca2+ oscillations based on the Ca2+-dependent modulation of the intermediate-conductance, Ca2+-activated K+ (IKCa) channel. The functioning of this model relies on the Ca2+-dependent activation, and the much slower Ca2+-dependent rundown of this channel. We have shown that Ca2+-dependent activation of the IKCa channels, the consequent membrane hyperpolarization and the resulting increase in Ca2+ influx may confer the positive feedback mechanism required for the ascending phase of the oscillation. The much slower Ca2+-dependent rundown process will conversely halt this positive loop, and establish the descending phase of the intracellular Ca2+ oscillation. We found that this simple model gives rise to intracellular Ca2+ oscillations when using physiologically reasonable parameters, suggesting that IKCa channels could participate in the generation of intracellular Ca2+ oscillations.     

Dynamics of action potential head-tail interaction during reentry in cardiac tissue: ionic mechanisms

In a sufficiently short reentry pathway, the excitation wave front (head) propagates into tissue that is partially refractory (tail) from the previous action potential (AP). We incorporate a detailed mathematical model of the ventricular myocyte into a one-dimensional closed pathway to investigate the effects of head-tail interaction and ion accumulation on the dynamics of reentry. The results were the following: 1) a high degree of head-tail interaction produces oscillations in several AP properties; 2) Ca(2+)-transient oscillations are in phase with AP duration oscillations and are often of greater magnitude; 3) as the wave front propagates around the pathway, AP properties undergo periodic spatial oscillations that produce complicated temporal oscillations at a single site; 4) depending on the degree of head-tail interaction, intracellular [Na(+)] accumulation during reentry either stabilizes or destabilizes reentry; and 5) elevated extracellular [K(+)] destabilizes reentry by prolonging the tail of postrepolarization refractoriness.     

Fast calcium wave propagation mediated by electrically conducted excitation and boosted by CICR

We have investigated synchronization and propagation of calcium oscillations, mediated by gap junctional excitation transmission. For that purpose we used an experimentally based model of normal rat kidney (NRK) cells, electrically coupled in a one-dimensional configuration (linear strand). Fibroblasts such as NRK cells can form an excitable syncytium and generate spontaneous inositol 1,4,5-trisphosphate (IP(3))-mediated intracellular calcium waves, which may spread over a monolayer culture in a coordinated fashion. An intracellular calcium oscillation in a pacemaker cell causes a membrane depolarization from within that cell via calcium-activated chloride channels, leading to an L-type calcium channel-based action potential (AP) in that cell. This AP is then transmitted to the electrically connected neighbor cell, and the calcium inflow during that transmitted AP triggers a calcium wave in that neighbor cell by opening of IP(3) receptor channels, causing calcium-induced calcium release (CICR). In this way the calcium wave of the pacemaker cell is rapidly propagated by the electrically transmitted AP. Propagation of APs in a strand of cells depends on the number of terminal pacemaker cells, the L-type calcium conductance of the cells, and the electrical coupling between the cells. Our results show that the coupling between IP(3)-mediated calcium oscillations and AP firing provides a robust mechanism for fast propagation of activity across a network of cells, which is representative for many other cell types such as gastrointestinal cells, urethral cells, and pacemaker cells in the heart.     

Heart rate variability biofeedback as a method for assessing baroreflex function: a preliminary study of resonance in the cardiovascular system

This study describes the use of a biofeedback method for the noninvasive study of baroreflex mechanisms. Five previously untrained healthy male participants learned to control oscillations in heart rate using biofeedback training to modify their heart rate variability at specific frequencies. They were instructed to match computer-generated sinusoidal oscillations with oscillations in heart rate at seven frequencies within the range of 0.01–0.14 Hz. All participants successfully produced high-amplitude target-frequency oscillations in both heart rate and blood pressure. Stable and predictable transfer functions between heart rate and blood pressure were obtained in all participants. The highest oscillation amplitudes were produced in the range of 0.055–0.11 Hz for heart rate and 0.02–0.055 Hz for blood pressure. Transfer functions were calculated among sinusoidal oscillations in the target stimuli, heart rate, blood pressure, and respiration for frequencies at which subjects received training. High and low target-frequency oscillation amplitudes at specific frequencies could be explained by resonance among various oscillatory processes in the cardiovascular system. The exact resonant frequencies differed among individuals. Changes in heart rate oscillations could not be completely explained by changes in breathing. The biofeedback method also allowed us to quantity characteristics of inertia, delay, and speed sensitivity in baroreflex system. We discuss the implications of these findings for using heart rate variability biofeedback as an aid in diagnosing various autonomic and cardiovascular system disorders and as a method for treating these disorders.     

Phase Dependent Sign Changes of GABAergic Synaptic Input Explored <Emphasis Type="Italic">In-Silicio</Emphasis> and <Emphasis Type="Italic">In-Vitro</Emphasis>

Inhibitory interactions play a crucial role in the synchronization of neuronal activity. Here we investigate the effect of GABAergic PSPs on spike timing in cortical neurons that exhibit an oscillatory modulation of their membrane potential. To this end we combined numerical simulations with in-vitro patch-clamp recordings from layer II/III pyramidal cells of the rat visual cortex. Special emphasis was placed on exploring how the reversal potential of the GABAergic synaptic currents (E_GABA) and the phase relations of the PSPs relative to the oscillation cycles affect the timing of spikes riding on the depolarizing peaks of the oscillations. The simulations predicted: (1) With E_GABA more negative than the oscillation minima PSPs are hyperpolarizing at all phases and thus delay or prevent spikes. (2) With E_GABA being more positive than the oscillation maxima PSPs are depolarizing in a phase-independent way and lead to a phase advance of spikes. (3) In the intermediate case where E_GABA lies within oscillation maxima and minima PSPs are either hyper- or depolarizing depending on their phase relations to the V_m oscillations and can therefore either delay or advance spikes. Experiments conducted in this most interesting last configuration with biphasic PSPs agreed with the model predictions. Additional theoretical investigations revealed the effect of these PSP induced shifts in spike timing on synchronization in neuronal circuits. The results suggest that GABAergic mechanisms can assume highly specific timing functions in oscillatory networks.Action Editor: Alain Destexhe     

Synchronization of oscillatory rhythms of stems and leaves

A previous report on the mechanism of diurnal oscillations is supplemented here by data concerning causes of irregularities in their oscillation trajectories. Cinematographic records showed that the final trajectory is significantly influenced by the circumnutation oscillations of the stem. Amplitudes of these oscillations which are small(ca 0.7 mm as compared with 5 X larger amplitudes of leaves when measured at the leaf tip) can be enlarged up to 10 times the value at the apical tip of the leaf. These nutations are responsible for side-deviations of space spirals of growing leaves in the direction of their shorter half axis. This explanation is based on the occurrence of side-deviations of leaf trajectories which correlate with the actual position of the nutation phase of the stem. Concurrent frequencies of the two oscillations (= diurnal rhythm) indicate that nyctinastic oscillations of the leaves are controlled by the same mechanism as is the circumnutation of the stem.