Large Negative Potential Research Articles

On the brightness variations of comet Halley at large heliocentric distances

Sporadic variations of its intrinsic brightness of up to 500%, with time scales as short as a few hours, has been exhibited by Halley's comet at large heliocentric distances (11-8 AU). It is shown that many of these brightness enhancements are closely correlated to the encounter of high-speed solar wind streams by the comet. It is proposed that during such periods the night side of the comet gets charged to numerically large negative electrostatic potentials, with consequent electrostatic levitation and blow-off of fine charged dust grains lying on it. This gives rise to the observed brightness variations.

Mechanism and Role of Divalent Cation Binding of Bacteriorhodopsin

Several observations have already suggested that the carboxyl groups are involved in the association of divalent cations with bacteriorhodopsin (Chang et al., 1985). Here we show that at least part of the protons released from deionized purple membrane (;blue membrane') samples when salt is added are from carboxyl groups. We find that the apparent pK of magnesium binding to purple membrane in the presence of 0.5 mM buffer is 5.85. We suggest this is the pK of the carboxyl groups shifted from their usual pK because of the proton concentrating effect of the large negative surface potential of the purple membrane. Divalent cations may interact with negatively charged sites on the surface of purple membrane through the surface potential and/or through binding either by individual ligands or by conformation-dependent chelation. We find that divalent cations can be released from purple membrane by raising the temperature. Moreover, purple membrane binds only about half as many divalent cations after bleaching. Neither of these operations is expected to decrease the surface potential and thus these experiments suggest that some specific conformation in purple membrane is essential for the binding of a substantial fraction of the divalent cations. Divalent cations in purple membrane can be replaced by monovalent, (Na(+) and K(+)), or trivalent, (La(+++)) cations. Flash photolysis measurements show that the amplitude of the photointermediate, O, is affected by the replacement of the divalent cations by other ions, especially by La(+++). The kinetics of the M photointermediate and light-induced H(+) uptake are not affected by Na(+) and K(+), but they are drastically lengthened by La(+++) substitution, especially at alkaline pHs. We suggest that the surface charge density and thus the surface potential is controlled by divalent cation binding. Removal of the cations (to make deionized blue membrane) or replacement of them (e.g. La(+++)-purple membrane) changes the surface potential and hence the proton concentration near the membrane surface. An increase in local proton concentration could cause the protonation of critical carboxyl groups, for example the counter-ion to the protonated Schiff's base, causing the red shift associated with the formation of both deionized and acid blue membrane. Similar explanations based on regulation of the surface proton concentration can explain many other effects associated with the association of different cations with bacteriorhodopsin.

Somatosensory evoked potentials (SEPs) and cortical single unit responses elicited by mechanical tactile stimuli in awake monkeys

The origins of surface recorded evoked potentials have been investigated by combining recordings of single unit responses and somatosensory evoked potentials (SEPs) from the postcentral gyrus of 4 alert macaque monkeys. Responses were elicited by mechanical tactile stimuli (airpuffs) which selectively activate rapidly adapting cutaneous mechanoreceptors, and permit patterned stimulation of a restricted area of skin. Epidurally recorded SEPs consisted of an early positive complex, beginning 8–10 msec after airpuff onset, with two prominent positive peaks (P15 and P25), succeeded by a large negative potential (N43) lasting 30 msec, and a late slow positivity (P70). SEPs, while consistent in wave form, varied slightly between monkeys. The amplitude of the early positive complex was enhanced by increasing the number of stimulated points, or by placing the airpuffs in the receptive fields of cortical neurons located beneath the SEP recording electrode. SEP amplitude was depressed when preceded 20–40 msec earlier by a conditioning stimulus to the same skin area. Single unit responses in areas 3b and 1 of primary somatosensory (SI) cortex consisted of a burst of impulses, beginning 11–12 msec after the airpuff onset, and lasting another 15–20 msec. Peak unitary activity occurred at 12–15 msec, corresponding to the P15 wave in the SEP. No peak in SI unit responses occurred in conjunction with the P25 wave. Although SI neurons fired at lower rates during P25, the lack of any peak in SI unit responses suggests that activity in other cortical areas, such as SII cortex, contributes to this wave. Most unit activity in SI cortex ceased by the onset of N43, and was replaced by a period of profound response depression, in which unit responses to additional tactile stimuli were reduced. We propose that the N43 wave reflects IPSPs in cortical neurons previously depolarized and excited by the airpuff stimulus. Late positive potentials (P70) in the SEP had no apparent counterpart in SI unit activity, suggesting generation at other cortical loci.

Drug-ionic channel interactions: single-channel measurements.

Ionic channels of excitable membranes are the basic site where ionic fluxes take place during the generation of action potentials. A variety of natural toxins, chemicals, and therapeutic drugs have been found to modify the gating kinetics of the Na+ channels, thereby altering the excitation pattern. Studies of such chemical modulations of Na+ channel gating provide the basis for understanding the mechanisms underlying the epilepsies and the actions of anticonvulsant drugs. Certain chemicals and toxins have been found to drastically slow the kinetics of the opening and closing of the Na+ channel. For example, batrachotoxin, the grayanotoxins, and the pyrethroids modify a population of the Na+ channels to give rise to an extremely slow opening and closing. Patch clamp techniques developed during the past few years permit measurements of the opening and closing of individual ionic channels. When an isolated membrane patch is depolarized, squared inward currents of about 1 picoampere in amplitude and 2 ms in duration are observed at 10 degrees C. After exposure of the membrane to batrachotoxin, open time is prolonged, single-current amplitude is greatly reduced, and channel opening is observed at large negative potentials, where no opening is expected to occur in normal preparations. In the batrachotoxin-poisoned membrane there are two separate groups of Na+ channels: one exhibiting normal characteristics and the other exhibiting a prolonged opening and reduced amplitude.

聴性脳幹反応と下丘

The role of the inferior colliculus (IC) to the auditory brainstem response (ABR) was investigated in rats by the following experiment consisting of; (1) observation of change in the ABRs and evoked potentials (EPs) of the IC before and after unilateral destruction of the cochlea. (2) observation of change in the wave form of EPs and ABRs before and after destruction of the IC. (3) recording of the EPs at various points in and around the IC. (4) search for the isopotential line in and around the IC. (5) recording of EPs to electrical stimulation of the IC. The EP of the central nucleus of the IC consists of one or two positive waves followed by a large negative wave. The wave form of the ABR seems to be a composite of a positive slow wave and several sequential fast wave-lets, and characteristics and origins of these two potentials are different to each other.The central nucleus of the IC is more important for generation of the positive slow component. A negative field is observed in the central nucleus of the IC, and a positive field surrounding this negative field is recorded as the positive slow wave of the ABR from the surface of the brain. A similar electrical potential field was also observed by the direct electrical stimulation of the IC, that is, a large negative potential was recorded at the central nucleus of the IC and a positive potential was observed at the surface of the brain, when the lateroventral part of the IC were stimulated electrically. Thus, the positive slow wave of the ABR is consisted mainly of this positive potential field, at least in latter part of the slow wave.The central nucleus of the IC might not be essential for generation of the several sequential fast waves of the ABR, because their latencies and amplitudes were not changed by destruction of the central nucleus of the IC. However, when the lesion was extended to or located in the lateroventral part of the IC, where the nerve fibers of the peripheral nuclei penetrate into the IC, potential V and VI were abolished whereas potential IV was remained unchanged. Thus, the structures peripheral to the IC play an important role for the generation of potential IV, and the lateoventral part of the IC is essential for generation of potential V and VI.

Entry of dust particles into planetary magnetospheres

While interplanetary dust constitutes a primary source of cosmic particulate matter in planetary magnetospheres, the debris produced by its impact with small satellites and ring material provides an important secondary source. Internal processes, such as volcanic activity, particularly in the smaller satellites, could result in a third source. In the case of the terrestrial magnetosphere there are also artificial (internal) sources: 1–10 μ sized Aℓ 2 O 3 particles injected by solid rocket mortar burns between near earth and geosynchronous orbit constitute one such source, while the fragments of larger bodies (artificial satellites) due to explosions (e.g., “killer satellites”) and collisions constitute another. Finally, if we include the purely induced cometary magnetosphere among planetary magnetospheres, the injection of cometary dust into it due to entrainment by the outflowing gases constitutes another source. As a result of being immersed in a radiative and plasma environment these dust grains get electrically charged up to some potential (positive or negative). Particularly in those regions where the magnetospheric plasma is hot and dense and their own spatial density is low, the dust grains could get charged to numerically large negative potentials. While this charging may have physical consequences for the larger grains, such as electrostatic erosion (“chipping”) and disruption, it also can effect the dynamics of the smaller grains. Indeed, the small but finite capacitance of these grains, which leads to a phase lag in the gyrophase oscillation of the grain potential, could even lead to the permanent magneto-gravitational capture of interplanetary grains within planetary magnetospheres in certain situations. Here we will review the sources of dust in planetary magnetospheres and discuss their physics and their dynamics under the combined action of both planetary gravitational and magnetospheric electromagnetic forces.

Evoked potentials recorded from scalp and spinous processes during spinal column surgery

Peroneal nerve evoked potentials were simultaneously recorded from scalp and from wire electrodes inserted into lumbar and thoracic spinous processes at multiple levels during surgery for correction of spinal column curvature in 43 patients. Spinal potentials progressively increased in latency rostrally. Over cauda equina and rostral spinal cord initially positive triphasic potentials were recorded. Over caudal spinal cord the response consisted of initial positive-negative diphasic potentials that merged with broad large negative and positive potentials. At rapid rates of stimulation, the initial diphasic component was stable but the subsequent potentials significantly diminished in amplitude. This suggests that the diphasic component reflects presynaptic activity arising in the intramedullary continuations of dorsal root fibers and that the subsequent components reflect largely postsynaptic activity. Scalp recordings at restricted bandpass (30–3000 c/sec) revealed well defined positive and negative potentials with mean peak latencies of 25.9 and 29.9 msec (P V-N 1). The amplitudes and latencies of P V-N 1 remained relatively stable throughout general anesthesia with halogenated agents which suggests that this component may be a reliable monitor of conduction within spinal cord afferent pathways during spinal surgery. Data are presented which suggest that selective filtering may help to distinguish faster frequency, synchronous axonal events from slower frequency, asynchronous axonal or synaptic events.

A controversial problem: modified Ising model in a random field

The effect of quenched impurities on a system having a commensurate-incommensurate (CI) phase transition is treated by real-space rescaling. A simplified form of the free energy is treated explicitly. New terms generated by the rescaling procedure do not modify the results. In D=3 dimensions, the Bragg peak shift (misfit) varies linearly with the chemical potential near the CI transition. The CI transition is killed for D<or=Dc=2. At the critical dimension, the misfit decreases exponentially for large negative chemical potentials. The model treated here may be considered a modified Ising model in a random field. The modification is a strong anisotropy of the interfaces separating the up and down domains.

Synaptic organization of eighth nerve afferents to cat dorsal cochlear nucleus.

The synaptic organization of eighth nerve afferents to the dorsal cochlear nucleus (DCN) of cats was studied using extracellular field potential analyses. The eighth nerve was electrically stimulated and potentials produced in the DCN characterized using single shocks, paired shocks, repetitive stimulation, and one-dimensional current source-density (CSD) analysis. Field potentials and CSD profiles were correlated with the laminated cytoarchitecture of the DCN. At least four major temporally discrete components can be identified in field potentials evoked by a single shock to the eighth nerve. The amplitude and polarity of these events depends on the layers in which they are recorded. A brief positive-negative deflection (the P1-N1) is present in all layers but is maximal in the deeper layers 3 and 4. The N1 has a peak latency of approximately 0.8 ms in these layers. The N1 in the deep layers is followed by a large negative potential, termed the N2, with a peak latency of about 1.6 ms. In the superficial layers (1 and 2), the N1 is followed by a small positive potential (the P2) occurring nearly simultaneously with the N2, Immediately following the N2 is another negative potential that is most clearly observed in layer 2. The layer 2 negative wave is termed N3 and is also identifiable on the repolarizing phase of the N2 in layers 3 and 4. The N3 in layer 2 can be followed by a positive potential, the P4. Simultaneous with the P4 is a small negative wave ion layer 1, termed the N4. The P4-N4 complex is observed in about half the recordings. Frequency-following tests indicate that both the N1 and N2 waves can follow shock trains up to 333 Hz. The N1 remains nearly constant in amplitude up to about 300 Hz and decreases as the stimulus frequency is raised to 500 Hz. The N2 decrements more rapidly than the N1 at frequencies above about 250 Hz and is considerably reduced at 500 Hz. The N2 sometimes shows an increased amplitude (by about 20-40%) between 100 and 250 Hz. A paired-shock paradigm was used to characterize further potentials. The N1 was little affected by prior stimulation for intervals greater than 5 ms. The N2 and N3 generally showed a small facilitation for shock intervals from about 7 to 30 ms, with a return to base line at longer intervals. The N4 and P4 (when present) were profoundly depressed for intervals from 7 to about 30 ms, with recovery to control values by 50 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Hydrogen ion block of the sodium pore in squid giant axons.

The block of squid axon sodium channels by H ions was studied using voltage-clamp and internal perfusion techniques. An increase in the concentration of internal permeant ions decreased the block produced by external H ions. The voltage dependence of the block was found to be nonmonotonic: it was reduced by both large positive and large negative potentials. The ability of internal ions to modify the block by external H+ is explained by a competition among these ions for a binding site within the pore. The nonmonotonic voltage dependence is consistent with this picture if the hydrogen ions are allowed to be permeant.

Reexamination of the double sucrose gap technique for the study of lobster giant axons. Theory and experiments

The double sucrose gap technique for the study of lobster giant axons has been reexamined. The leakage behavior of the system cannot be successfully modeled by conventional sucrose gap theory, but is accounted for by the McGuigan-Tsien model that takes into account the cable properties of membrane under sucrose. The facts of high-leakage conductance and the ability to maintain large resting potentials in the face of low sucrose gap resistance lead to a hypothesis that membrane resistance under sucrose is very low because of a large negative surface potential. Computer simulations of the leakage behavior of the conventional gap model and the McGuigan-Tsien model were compared with experimental measurements on lobster axons using normal sucrose or sucrose doped with Na+, Ca2+ or La3+ ions. As the concentration of doping ion increased, the leakage rose, but the species of doping ion had more influence on leakage than gap resistance. At equal gap resistance, leakage decreased with an increase in valence of the doping species. Leakage was even lower in La-doped sucrose at 20 M omega gap resistance than in normal sucrose at 200 M omega gap resistance. Resting potentials decreased with decreasing gap resistance and increasing valence of the doping species. Resting potential behavior was successfully simulated with a hybrid model consisting of a point node flanked by infinite cables and a shunt between ground and the voltage-measuring pool. The data support the hypothesis that the membrane resistance under sucrose is low and that it can be raised by doping the sucrose with multivalent cations, with La3+ being particularly effective. Both the leak conductance and resting potential are influenced more by membrane under sucrose than membrane in the node. The experiments also demonstrate that doping with La3+ vastly improves the stability and longevity properties of the lobster axon preparation.

Isolation, molecular and functional properties of the C-terminal domain of colicin A.

Partial proteolytic digestion of colicin A with bromelain allowed the isolation of a 20-kd fragment. This fragment has been purified to homogeneity and its molecular properties have been studied. The sequence of the 54 N-terminal amino acid residues has been determined by automated Edman degradation. This sequence is identical to that of the predicted amino acid sequence of the 20-kd C-terminal part of the colicin A polypeptide deduced from the nucleotide sequence of the caa gene. This polypeptide can produce channels in phospholipid planar bilayers of the same size as those formed by colicin A. However, the voltage-dependence for opening and closing was drastically altered in the peptide fragment channels. The latter, in contrast to colicin A channels, remained open over a wide range of voltage. Large negative potentials were required to close the peptide fragment channels although opening took place in the same voltage range as for colicin A ionic pores.

A d-d Tandem Mirror Reactor with Central-Cell Potential Modification

A conceptual tandem-mirror reactor (TMR) configuration consists of a solenoidal central-cell with its ends plugged by a combination of electrostatic and magnetic fields. The magnetic fields in the end plug also provide MHD stability. The electrostatic plugs for ions and electrons are created by combining hot electron plasmas and neutral beams for fueling and pumping. A large negative potential may be formed in the end plug to contain central cell electrons, but the central cell floating potential /phi/ /SUB f/ is driven negative as charge neutrality is maintained. Cat-d TMR plasma performance is assessed with respect to standard (positive), neutral and negative central cell potential operating modes. It is determined that the plasma Q for a 2000 MW fusion power reactor is peaked for central cell potential /phi/ /SUB f/ near zero. This is because on one hand, the ion-loss cone is bigger for positive /phi/ /SUB f/ and the ion plug electrons must overcome larger /phi/ /SUB f/ + /phi/ /SUB c/ and hence more ECH is required to build the ion plug, and, on the other hand, the electron loss-cone is bigger for negative /phi/ /SUB f/ and synchrotron losses are severe. A zero-dimensional plasma physics model formore » the density and power balance of a Cat-d TMR has been developed from an existing code that models a d-t TMR operating with a positive central cell potential. The new Cat-d code models all potential operating modes and has been benchmarked.« less

Mechanism of the production of the negative endocochlear DC potential in the guinea pig.

Changes in endocochlear DC potential (EP) and potassium ion concentrations in endolymph were measured simultaneously during anoxia or during perfusion of the perilymphatic space with furosemide, 10(-2)M, in normal and kanamycin-deafened guinea pigs. The potassium ion conductance (Gk) through the cochlear partitions was calculated. Thirty minutes after the onset of anoxia, the Gk is 22.1 microM/min/mV in normal guinea pigs and 4.8 microM/min/mV in kanamycin-deafened guinea pigs. At that time the EP is -29.5 mV in normal guinea pigs and 1.4 mV in kanamycin-deafened guinea pigs. In the early stage of anoxia the rate of potassium ion concentration decrease in the endolymph per unit time is greater in normal guinea pigs than in kanamycin-deafened guinea pigs. These results suggest a rapid increase in the permeability of potassium ions in the organ of Corti in the early stage of anoxia might produce a large negative potassium ion diffusion potential or negative EP in normal guinea pigs and the failure to develop the negative EP in kanamycin-deafened guinea pigs might be due to the lack of such a rapid increase in the permeability because of the loss of the hair cells.

The control of tonic tension by membrane potential and intracellular sodium activity in the sheep cardiac Purkinje fibre.

Intracellular Na activity (aiNa) was measured with recessed-tip, Na-selective micro-electrodes in voltage-clamped sheep cardiac Purkinje fibres. Tension was measured simultaneously. aiNa was increased reversibly either by exposing the preparation to K-free, Rb-free solution of by adding the cardioactive steroid strophanthidin. An increase of aiNa produced an increase of tonic tension which was larger at depolarized membrane potentials. At sufficiently negative membrane potentials, changes of aiNa (over the range 6-30 mM) had no effect on tonic tension. Therefore, both an increase of aiNa and a depolarization are required to increase tonic tension. It is concluded that either a low level of aiNa or a large negative membrane potential is sufficient to maintain a low intracellular Ca concentration. Tonic tension was measured as a function of aiNa. At a given membrane potential the relationship can be described empirically by an equation of the form: tonic tension = b(aiNa)y, where y is a constant and b depends on membrane potential. In five experiments y was found to be 3.7 +/- 0.7 (mean +/- S.E.M.) over a range of potentials from -60 to -10 mV. Tonic tension was measured as a function of membrane potential. At a given aiNa the relationship can be described approximately as: tonic tension = k exp (aV), where a is a constant and k depends on aiNa. In five experiments a was found to be 0.06 +/- 0.01 mV-1 (mean +/- S.E.M.). A depolarization of 10 mV increases tonic tension by the same amount as does an increase of aiNa that is equivalent to a 3.7 mV change of the Na equilibrium potential, ENa. Hence ENa is nearly 3 times more effective than membrane potential in controlling tonic tension. During a prolonged depolarization (several minutes) the initial increase of tonic tension decays gradually. This is associated with a fall of aiNa. The relationship between tonic tension and aiNa is similar to that seen when aiNa is increased by inhibiting the Na pump. It is concluded that the fall of aiNa is responsible for the decay of tonic tension. The changes of tonic tension reported in this paper are consistent with the effects of aiNa and membrane potential on a voltage-dependent Na-Ca exchange. The possibility that a voltage-dependent Ca channel contributes to tonic tension is also discussed.

Muscarine-sensitive voltage-dependent potassium current in cultured murine spinal cord neurons

Muscarine produced membrane depolarization and decreased membrane conductance of mouse spinal cord neurons in dissociated cell culture. When the neurons were voltage clamped, muscarine evoked inward currents which increased with membrane depolarization and decreased with membrane hyperpolarization. However, the muscarine-induced inward currents did not invert at large negative potentials, suggesting that muscarine decreased a voltage-dependent potassium current (m-current) [2]. Using the voltage-jump current-relaxation technique, m-current was demonstrated in spinal cord neurons and shown to be a muscarine-sensitive potassium current.

Space Shuttle Orbiter charging

This paper considers the charging of the Space Shuttle Orbiter by energetic particles of environmental origin and from emission by accelerators. The results indicate that precipitating electrons quickly induce large voltages. High voltages may also occur when onboard accelerators inject energetic beams into the high altitude plasma. A significant conclusion from electron beam experiments is that the rockets charged to positive potentials much less than anticipated from the theory of probes in a quiescent plasma. Elementary theories predict the large negative potentials observed by firing energetic ions and predict severe differential charging of the Orbiter.

Modification of single Na+ channels by batrachotoxin.

The modifications in the properties of voltage-gated Na+ channels caused by batrachotoxin were studied by using the patch clamp method for measuring single channel currents from excised membranes of N1E-115 neuroblastoma cells. The toxin-modified open state of the Na+ channel has a decreased conductance in comparison to that of normal Na+ channels. The lifetime of the modified open state is drastically prolonged, and channels now continue to open during a maintained depolarization so that the probability of a channel being open becomes constant. Modified and normal open states of Na+ channels coexist in batrachotoxin-exposed membrane patches. Unlike the normal condition, Na+ channels exposed to batrachotoxin open spontaneously at large negative potentials. These spontaneous openings apparently cause the toxin-induced increase in Na+ permeability which, in turn, causes membrane depolarization.

Bioelectric activity in the rabbit ear regeneration.

A 1-cm-diameter hole was punched through rabbits' ears. The surface potentials during wound healing of regenerating (normal) and partially and nonregenerating (decartilaged) ears were measured. The time sequence of these surface potentials were similar to those reported to occur in regenerating amphibians forelimbs. A small positive potential was observed for about 1 week, and this was followed by a larger negative potential of up to 20 mV, with different durations. The duration of the positive potential was about the same as which was observed in amphibians. The duration and the amplitude of the negative potential were greatest for completely regenerating ears with overgrowth, smaller for partially regenerating ears, and smallest for the nonregenerating ears. The surface potential was localized. If a nipple-shaped outgrowth developed after the hole was closed, the surface potential was observed only on this outgrowth; immediately outside it, the potential was normal. We concluded that the negative bioelectric activity accompanies growth, and while growth continues, negative bioelectric potential continues.

One-dimensional static sheath characteristics

The boundary layer between an electrode biased to a large negative potential (relative to the electron temperature eφ≫kTe ) and a collisionless argon plasma (n∼1×109 cm−3, kTe ∼2.5 eV) was studied using Langmuir probes. A simple model based on Child’s law, including finite electron temperature effects, was fit to data obtained from both cold and emitting probes. A convenient method was developed to locate the sheath edge using cold probes. The emitting probe experiments demonstrated what we believe is a new technique for measuring the potential within the non-neutral sheath region.