Membrane Electrical Characteristics Research Articles

Development of gerbil medial superior olive: integration of temporally delayed excitation and inhibition at physiological temperature.

The sensitivity of medial superior olive (MSO) neurons to tens of microsecond differences in interaural temporal delay (ITD) derives in part from their membrane electrical characteristics, kinetics and timing of excitatory and inhibitory inputs, and dendrite structure. However, maturation of these physiological and structural characteristics are little studied, especially in relationship to the onset of auditory experience. We showed, using brain slices at physiological temperature, that MSO neurons exhibited sensitivity to simulated temporally delayed (TD) EPSCs (simEPSC), injected through the recording electrode, by the initial phase of hearing onset at P10, and TD sensitivity was reduced by block of low threshold potassium channels. The spike generation mechanism matured between P10 and P16 to support TD sensitivity to adult-like excitatory stimuli (1-4 ms duration) by P14. IPSP duration was shorter at physiological temperature than reported for lower temperatures, was longer than EPSP duration at young ages, but approached the duration of EPSPs by P16, when hearing thresholds neared maturity. Dendrite branching became less complex over a more restricted time frame between P10 and P12. Because many physiological and structural properties approximated mature values between P14 and P16, we studied temporal integration of simEPSCs and IPSPs at P15. Only a narrow range of relative onset times (< 1 ms) yielded responses showing sensitivity to TD. We propose that shaping of excitatory circuitry to mediate TD sensitivity can begin before airborne sound is detectable, and that inhibitory inputs having suboptimal neural delays may then be pruned by cellular mechanisms activated by sensitivity to ITD.

Electrical Characteristics of Suburothelial Cells Isolated From the Human Bladder

We measured the membrane electrical characteristics as well as the response to adenosine triphosphate of cells isolated from the suburothelial layer of the bladder. Suburothelial cells were isolated from biopsy samples of human bladder by collagenase disruption. Electrophysiological measurements were done under current and voltage clamp to record membrane potential and ionic currents using patch pipettes with a K+ based filling solution. Intracellular [Ca2+] was measured with Fura-2. Cells were different from epithelial cells by their spindle-shaped appearance with projections at either end. The cells stained for vimentin but epithelial and smooth muscle cells did not. The cells had small membrane capacitance (27 +/- 16 pF) and a specific membrane resistance of 90 +/- 48 x 10(9) Omega cm2. Average membrane potential was -63 +/- 14 mV but cells showed spontaneous spikes or random fluctuations of membrane potential. A small net inward current was superimposed by a larger outward current. Inward current was attenuated by the removal of extracellular Ca. Outward current showed large spontaneous fluctuations and was greatly decreased by 30 mM tetraethyl ammonium chloride. Adenosine triphosphate (30 to 100 microM) elicited an inward current of about 50 pA and large intracellular Ca2+ transients. These cells are electrically active which, in conjunction with the previous observation of connexin 43 labeling, suggests that they could act as an electrical network. A quantitative model of voltage distribution in such a network after the generation of inward current suggests that individual cells could not act as pacemakers, but rather a group of simultaneously activated cells could exert a peripheral excitatory effect that would amplify the magnitude of the original response. The implications of this in terms of bladder sensation are discussed.

Electrochemical parameters of sulfonated poly(ether ether sulfone) membranes in HCl solutions determined by impedance spectroscopy and membrane potential measurements

Electrical and electrochemical properties of different samples of sulfonated poly(ether ether sulfone) (SPEES) membranes with different sulfonation degrees (0%, 5% and 10%) were determined measuring the electrical resistance and concentration potential with the membranes in contact with HCl solutions at different concentrations. Impedance spectroscopy (IS) was used to determine the membrane resistance ( R m) using equivalent circuits as models, and the results show how the sulfonation clearly affects the membrane electrical characteristics, strongly reducing the R m and also changing the type of circuit associated with the different membranes. The determination of both the proton transport number and the membrane permselectivity to H + ions in sulfonated samples was performed by measuring concentration potentials (Δ φ). Proton diffusion in the sulfonated membranes were determined from R m and Δ φ values and a strong reduction in the membrane electrical resistance and an increase in the H + diffusion coefficient was observed with the increase of the sulfonation degree. A chemical characterization of the surface of nonsulfonated and sulfonated samples was also carried out by X-ray photoelectron spectroscopy (XPS).

Studies on the prevention of nigericin action in neuroblastoma X glioma hybrid (NG108-15) cells.

Electrophysiological analysis of neuroblastoma X glioma hybrid (NG108-15) cells was used as an in vitro neuronal model system to evaluate antagonists of the K+-selective carboxylic ionophore, nigericin. Changes in membrane electrical characteristics induced by nigericin with and without the simultaneous administration of antagonists were measured using intracellular microelectrode techniques. Bath application of nigericin (3 microM) produced a severe hyperpolarization and blocked the generation of action potentials in response to electrical stimulation. Simultaneous administration of nigericin plus the Na+-K+ pump inhibitor ouabain or drugs known to influence Ca++ signaling in cells, i.e., quinidine, compound R24571, verapamil or haloperidol, was able to significantly attenuate the hyperpolarization. All antagonists acted in a concentration-dependent manner. However, nigericin plus maximally effective concentrations of ouabain (1 microM), verapamil (3 microM) and haloperidol (3 and 10 microM) resulted in moderate-to-severe depolarization by the end of 24 min. superfusions, suggesting that the concentrations of antagonists were excessive and that NG108-15 cell damage had occurred. In addition, none of the compounds studied was able to effectively prevent nigericin-induced blockade of action potentials. Thus, none of these antagonists appears suitable for transition to in vivo antidotal protection studies.

Sulfonated poly(ether ether sulfones): Characterization and study of dielectrical properties by impedance spectroscopy

In this work, three samples of sulfonated polysulfones of different sulfonation degree have been characterized, and the electrical properties of dense membranes based on them have been evaluated. The polymers were characterized spectroscopically, and by their inherent viscosity, and water absorption. Electrical characterization of membranes was carried out on dense membranes in contact with NaCl solutions, by impedance spectroscopy (IS) measurements using equivalent circuits as models. The results showed how the sulfonation clearly affected the membrane electrical characteristics, strongly reducing the membrane resistance, and also changing the type of circuit associated to the membrane, which could be related to the increase of electrolyte taken by the membrane when the sulfonation degree increased. Concentration dependence of the electrical parameters was also studied.

Comparative effects of carboxylic ionophores on membrane potential and resistance of NG108-15 cells

Comparative analyses were conducted to determine the effects of Na + (monensin, MON), K + (nigericin, NIG) and Ca 2+ (A23187) selective carboxylic ionophores on differentiated NG108-15 (neuroblastoma X glioma hybrid) cells. Alterations in membrane potential (V m), input resistance (Rin) and electrically induced action potential generation were measured using intracellular microelectrode techniques in cells treated with 0.1–30 μ m MON and NIG and 0.1–10 μ m A23187. Responses to the ionophores were similar in that membrane hyperpolarization and unchanged R in predominated with all three compounds. However, significant differences between the ionophores were also detected. MON- and A23187-induced hyperpolarization was generally maintained throughout the 24-min superfusion whereas that produced by NIG diminished with time or was replaced by depolarization. In addition, action potential generation was blocked by NIG, whereas MON had no effect and action potential alterations were evident only with the highest A23187 concentration (10 μ m). This study represents the initial comprehensive analysis of the effects of carboxylic ionophores on membrane electrical characteristics of an intact cell system and forms the basis for subsequent work using NG108-15 cells as a model system to evaluate potential therapeutic treatments against the carboxylic ionophores.

Effects of neutral ionophores on membrane electrical characteristics of NG108-15 cells

The effects of several K +-selective neutral ionophores on membrane electrical characteristics of differentiated NG108-15 (neuroblastoma X glioma hybrid) cells were examined. Specifically, alterations in membrane resting potential ( V m), input resistance ( R in) and electrically-induced action potential generation were determined upon bath application of enniatin (0.1–10 μg/ml), nonactin (0.1–10 μM) and valinomycin (0.1–10 μM). Although some cells exhibited a slight hyperpolarization and/or reduced R in, i.e. membrane electrical correlates of enhanced K + loss, neither V m nor R in were significantly altered by any of the ionophores. However, valinomycin and especially nonactin affected action potentials induced by electrical stimulation. This was apparent in the ablation of action potentials in some cells and in the occurrence of degenerative changes in action potential shape in others. The simultaneous administration of the neutral ionophores and the protonophore CCCP or the superfusion of enniatin, nonactin or valinomycin in high (50 mM) glucose-containing physiological solution did not yield more extensive alterations in V m or R in. These data suggest that the neutral ionophores are unable to materially enhance K + flux above the relatively high resting level in NG108-15 cells. Thus, alterations in action potentials appear to be unrelated to K + transport activity.

Effects of protonophores on membrane electrical characteristics in NG108-15 cells.

Studies were conducted to determine the effects of bath application of the protonophores carbonyl cyanide m-chlorophenylhydrazone (CCCP) and carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone (FCCP) on membrane electrical characteristics of differentiated NG108-15 (neuroblastoma X glioma hybrid) cells. Membrane resting potential (Vm), input resistance (R(in)) and electrically induced action potential generation were measured using intracellular micro-electrode techniques. Both compounds produced concentration-dependent depolarization rather than the hyperpolarization commonly found with other central mammalian neurons. CCCP and FCCP also reduced R(in) and disrupted the generation of action potentials in a concentration-dependent manner. The contribution of the observed alterations to the in vivo toxicity of these compounds remains to be established.

Prevention of monensin-induced hyperpolarization in NG108-15 cells.

The NG 108-15 (neuroblastoma X glioma hybrid) cell line was used as an in vitro neuronal model to evaluate potential antagonists of the Na+-selective carboxylic ionophore monensin. Changes in membrane electrical characteristics induced by monensin with and without the simultaneous administration of antagonists were measured using intracellular microelectrode techniques. Bath application of monensin (3 microM) produced a hyperpolarization of approximately = 35 mV. Monensin also altered the generation of action potentials in response to electrical stimulation in 14 of 24 (58%) exposed cells, as evident in a partial or complete loss of action potentials or in an alteration of action potential waveform. The antagonists used were Na+-K+ pump inhibitor ouabain (1-3 microM), the Ca2+dependent K+ channel blocker quinine (3-30 microM) or drugs known to influence Ca2+ signaling in cells, i.e., trifluoperazine (3-10 microM), verapamil (1-10 microM) or chlorpromazine (3-30 microM). On a molar basis, ouabain was the most and trifluoperazine the least effective of the antagonists. Quinine, verapamil and chlorpromazine all prevented the development of the hyperpolarization in an approximate concentration-dependent manner. However, none of these drugs was able to block the effects of monensin on action potentials. Indeed, high concentrations of the antagonists that were most effective in preventing the hyperpolarization accentuated impairments in action potential generation and also reduced input resistance in many cells. Thus, none of these antagonists appears suitable for transition to in vivo antidotal protection studies.

Role of hemoglobin in regulation of membrane electrical properties and erythrocyte volume

Erytyrocyte volume in neonates is 25.8% greater than in women. Electrophoretic erythrocyte mobility was the same in neonates and in parturient women. The results obtained indicate that the more heterogeneous the hemoglobin system, the more heterogenous are erythrocyte membrane electrical characteristics.

Calmodulin antagonists induce changes in lens permeability and transparency.

Calmodulin has been shown to perform several important functions in the lens including regulation of the plasma membrane Ca(2+)-ATPase. This study investigated the effects of a variety of different CaM antagonists on rat lens membrane potential, membrane resistance, intracellular Na+ and Ca2+ content and transparency, in order to examine the role of CaM in control of lens membrane permeability. W7, calmidazolium and trifluoperazine caused biphasic changes in lens membrane electrical characteristics. Phase 1 consisted of a depolarization of the membrane potential and an increase in resistance, indicating that K+ channels were being blocked. This was confirmed by application of the K+ channel antagonist, quinine, which inhibited Phase 1 changes. Phase 2 was a further depolarization coupled with a decrease in resistance, indicating the activation of a cation conductance. Application of W7 in low Na+ medium slowed the Phase 2 depolarization and decrease in resistance indicating that Na+ is the main charge carrier through the activated conductance. The CaM inhibitors also led to a large increase in the Na+ and Ca2+ contents of the lens. W5, a less potent analogue of W7, caused a depolarization and increase in membrane resistance, but no Phase 2 changes were observed. Na+ and Ca2+ contents were similar to control lenses after 4 hours incubation in 200 microM W5. In addition, exposure to W7, TFP and calmidazolium resulted in a loss of transparency, while W5 treated lenses remained clear. It appears, therefore, that CaM is involved in control of lens membrane permeability. Loss of control of these channels leads to catastrophic changes in the intracellular ionic environment and hence opacification of the lens.

Electrical characteristics of stomatal guard cells: The ionic basis of the membrane potential and the consequence of potassium chlorides leakage from microelectrodes

The membrane electrical characteristics of stomatal guard cells in epidermal strips from Vicia faba L. and Commelina communis L. were explored using conventional electrophysiological methods, but with double-barrelled microelectrodes containing dilute electrolyte solutions. When electrodes were filled with the customary 1-3 M KCl solutions, membrane potentials and resistances were low, typically decaying over 2-5 min to near-30 mV and <0.2 kω·cm(2) in cells bathed in 0.1 mM KCl and 1 mM Ca(2+), pH 7.4. By contrast, cells impaled with electrodes containing 50 or 200 mM K(+)-acetate gave values of-182±7 mV and 16±2 kω·cm(2) (input resistances 0.8-3.1 Gω, n=54). Potentials as high as (-) 282 mV (inside negative) were recorded, and impalement were held for up to 2 h without appreciable decline in either membrane parameter. Comparison of results obtained with several electrolytes indicated that Cl(-) leakage from the microelectrode was primarily responsible for the decline in potential and resistance recorded with the molar KCl electrolytes. Guard cells loaded with salt from the electrodes also acquired marked potential and conductance responses to external Ca(2+), which are tentatively ascribed to a K(+) conductance (channel) at the guard cell plasma membrane.Measurements using dilute K(+)-acetate-filled electrodes revealed, in the guard cells, electrical properties common to plant and fungal cell membranes. The cells showed a high selectivity for K(+) over Na(+) (permeability ratio PNa/PK=0.006) and a near-Nernstian potential response to external pH over the range 4.5-7.4 (apparent PH/PK=500-600). Little response to external Ca(2+) was observed, and the cells were virtually insensitive to CO2. These results are discussed in the context of primary, charge-carrying transport at the guard cell plasma membrane, and with reference to possible mechanisms for K(+) transport during stomatal movements. They discount previous notions of Ca(2+)-and CO2-mediated transport control. It is argued, also, that passive (diffusional) mechanisms are unlikely to contribute to K(+) uptake during stomatal opening, despite membrane potentials which, under certain, well-defined conditions, lie negative of the potassium equilibrium potential likely prevailing.

Electrophotoluminescence and the electrical properties of the photosynthetic membrane. I. Initial kinetics and the charging capacitance of the membrane

Preilluminated chloroplast membranes, and particularly hypotonically swollen vesicles (blebs), give rise to a strong characteristic luminescence (electrophotoluminescence, EPL; Ellenson and Sauer, 1976, Photochem. Photobiol., 23:113-123; Arnold and Azzi, 1971, Photochem. Photobiol., 14:233-240) during the application of a strong external electric field. A detailed kinetic study of EPL was carried out and the initial kinetics from the field onset are reported here. The fast rise time (less than 0.2 mus) of the applied external electric field together with a high instrumental time resolution allowed the observation of a characteristic delay (lag time) between the field onset and the appearance of the induced emission. The lag time decreased with increase in the applied field strength and/or the conductivity of the suspension and is interpreted to be a consequence of (a) the necessity to reach a threshold electrical potential difference in the bleb membrane, below which no emission can be triggered, and (b) the finite time required to attain such a transmembranal field during the charging process of the membrane. A quantitative analysis, connecting the lag time, the controllable experimental parameters, and the membrane electrical characteristics is presented. Its verification was carried out in both size-selected and heterogeneous bleb populations. In the latter, experiments were consistent with the assumption that the lag time reflects the charging of the largest blebs. The results indicate (a) the possibility of directly measuring the specific membrane capacitance, yielding an estimate of Cm = 1.2 +/- 0.3 microF/cm2 (the precision being particle size-homogeneity dependent); (b) A minimal transmembranal potential difference (of approximately 240 mV) is necessary to induce electrophotoluminescence; and (c) the lag duration depends on the time elapsed between the preillumination and the external field application. Correlated with the study of ionophore effects on the lag time, this suggests additivity of the light- and field-induced transmembrane potentials in attaining the threshold for emission.

Immunological, biochemical, ultrastructural, and electrophysiological characteristics of a human glioblastoma-derived cell culture line.

This report presents the results of a study using multiple techniques of the established human cell line, LM, which has been developed in culture medium from a patient with a right temporoparietal glioblastoma. This cell line has human subtetraploid karyotype and has several features of a transformed line in culture. These include continuous propagation for 10 years, ability to form tumor nodules when transplanted into immunologically suppressed hamsters, and pleomorphic appearance. Ultrastructurally, it is characterized by multiple nuclei, few actin cables, and numerous surface-membrane microvilli, as well as abundant 9- to 10-nm cytoplasmic filaments. By its immunological reactivity, the line can be shown to contain glial fibrillary acidic protein at low levels, consistent with its glial origin and continued nature. Dibutyryl cyclic adenosine monophosphate (db-cAMP) induces formation of long astrocytic-like processes as well. Its membrane electrical characteristics include a low resting membrane potential and short time constant. Used in a microtiter antiglioma antibody cytotoxicity assay, LM yields a positive reaction to antibodies in the sera of 80% of patients with astrocytomas and only 9% of normal blood-bank donors, suggesting that it shares common antigens with other astrocytic tumor lines. The varied characteristics of this glioblastoma-derived line emphasize the "multiforme" nature on the neoplasm and suggest that for characterization of any such line, multiple parameters are necessary to allow comparison with other long-term glioblastoma lines in the literature. The usefulness of the LM line in in vitro cell biological, immunological, chemotherapeutic, and radiobiological studies of gliomas makes such efforts very worthwhile.

Pancreatic islet cells: electrogenic and electrodiffusional control of membrane potential.

1. Responses of the membrane electrical characteristics of mouse pancreatic islet cells to ionic environmental changes have been used to assess the role of [Na]0 and [K]0 in the control of membrane potential, i.e. by electrodiffusion or via an electrogenic sodium pump. Islet cell electrical properties were measured in vitro with intracellular glass micro-electrodes. 2. Substitution of LiCl for extracellular NaCl did not change the islet cell membrane potential significantly in low (2.8 mM) glucose solutions, but readmission of NaCl caused a transient hyperpolarization (membrane potential maximum: -70 mV) in high glucose; when choline chloride was substituted for NaCl no hyperpolarization was observed on NaCl re-admission. 3. Superfusion with K-free solution gave no marked change in membrane potential during 30 min incubation in either low (2-8 mM) or high (28 mM) glucose concentrations but longer periods of exposure to K-free solutions caused progressive depolarization. 4. Readmission of K+ induced a transient hyperpolarization of up to 30 mV magnitude and 10 min duration in the presence of high (28 mM) but not low glucose (2-8 mM) concentrations. At the level of maximum hyperpolarization the membrane potential reached -60 mV, the electrical activity induced by the high glucose concentration being concurrently completely blocked. Replacement of [Cl]0 by isethionate accentuated these effects. 5. Ouabain, 10(-3) M, or a decrease in temperature from 37 to 7 degrees C depolarized the islet cells and blocked the transient hyperpolarization induced by readmission of K+. 6. Diphenylhydantoin, 1-5 times 10(-4) M, caused a significant hyperpolarization of the islet cells in low glucose (2-8 mM) and inhibited the electrical activity induced by high glucose (28 mM) or tolbutamide (0-7 mM). 7. It is concluded from these results that both an electrogenic and ionic component contribute to the membrane potential of the mouse pancreatic islet cell although electrodiffusional control normally predominates; acceleration of the Na-K exchange pump by diphenylhydantoin inhibits glucose-induced electrical activity. These findings are discussed in relation to the permeability characteristics of the islet cell membrane and the mechanism of insulin release.

The role of protons in determining membrane electrical characteristics in Chara corallina.

The value of the potential difference between the vacuole and the external medium,ψvo, and the effects of metabolic inhibitors upon it indicate that, under certain external conditions, there are two main factors determining the potential across the plasmalemma. At all external pH there is a passive diffusion potential and at pH≧6 there is an active electrogenic component of potential. Calculations of ionic permeabilities of K+, Na+ and Cl− from their respective passive fluxes and application of the Goldman equation indicate that H+ permeability is approximately 25 times K+ permeability at pH 4 and 5 and possibly at pH≧6.ψvo does not respond to increases in [K+]0 when a large electrogenic component of potential is present, even though the calculated value ofPK under these conditions is such as to predict significant changes inψvo. It is suggested that this anomaly may be due to intrinsic properties of the electrogenic pump. There is evidence that the electrogenic pump is an active H+ efflux which calculations indicate is about 12 nmoles m−2 sec−1 at pH 5. However the electrogenic potential does not appear to be related to formation of acid and alkali regions in the external solution adjacent to cells ofChara.

Nerve membrane electrical characteristics near the resting state.

An experimental analysis of the squid axon membrane impedance in the vicinity of the resting state and as a function of frequency is presented. Particular attention was devoted to the measurement of theresonance frequency, for which the absolute magnitude of the impedance attains its maximum value, in different, extracellular solutions, at various temperatures and in the presence of constant depolarizations or hyperpolarizations.

Specifications for nerve membrane models

The limitations of models which can generate action potentials are discussed and reasons are given for testing all proposed membrane models by comparison with voltage clamp data. Some background information is provided and the voltage clamp methodology reviewed. Many of the membrane electrical characteristics measured by this technique are discussed and some recent observations are given to illustrate the additional data against which models should now be tested. Selected proposals for membrane models are reviewed and compared with one another and with voltage clamp measurements.

Internally perfused squid axons studied under voltage clamp conditions. II. Results. The effects of internal potassium and sodium on membrane electrical characteristics

Internally perfused squid axons studied under voltage clamp conditions. II. Results. The effects of internal potassium and sodium on membrane electrical characteristics

Electronic Control of Some Active Bioelectric Membranes

Special purpose real-time analog computers are used to measure and control nerve membrane or current in a squid axon or a single frog node. Under current control, the membrane has a region of discontinuity and an action potential rather similar to that observed in normal impulse propagation. With control, the current pattern is a continuous function of the potential, and a negative resistance is found in the region of discontinuity for the current-controlled membrane. The membrane's electrical characteristics may therefore be compared with some two-terminal transistor switching circuits.