Slow Changes In Membrane Potential Research Articles

The mitochondrial ATP synthase as an ATP consumer-a surprising therapeutic target.

The mitochondrial F1 Fo -ATP synthase uses a rotary mechanism to synthesise ATP. This mechanism can, however, also operate in reverse, pumping protons at the expense of ATP, with significant potential implications for mitochondrial and age-related diseases. In a recent study, Acin-Perez etal (2023) use an elegant assay to screen compounds for the capacity to selectively inhibit ATP hydrolysis without affecting ATP synthesis. They show that (+)-epicatechin is one such compound and has significant benefits for cell and tissue function in disease models. These findings signpost a novel therapeutic approach for mitochondrial disease.

Suppression of epileptiform activity by a single short-duration electric field in rat hippocampus in vitro

The mechanisms behind the therapeutic effects of electrical stimulation of the brain in epilepsy and other disorders are poorly understood. Previous studies in vitro have shown that uniform electric fields can suppress epileptiform activity through a direct polarizing effect on neuronal membranes. Such an effect depends on continuous DC stimulation with unbalanced charge. Here we describe a suppressive effect of a brief (10 ms) DC field on stimulus-evoked epileptiform activity in rat hippocampal brain slices exposed to Cs(+) (3.5 mM). This effect was independent of field polarity, was uncorrelated to changes in synchronized population activity, and persisted during blockade of synaptic transmission with Cd(2+) (500 μM). Antagonists of A(1), P(2X), or P(2Y) receptors were without effect. The suppressive effect depended on the alignment of the external field with the somato-dendritic axis of CA1 pyramidal cells; however, temporal coincidence with the epileptiform activity was not essential, as suppression was detectable for up to 1 s after the field. Pyramidal cells, recorded during epileptiform activity, showed decreased discharge duration and truncation of depolarizing plateau potentials in response to field application. In the absence of hyperactivity, the applied field was followed by slow membrane potential changes, accompanied by decreased input resistance and attenuation of the depolarizing afterpotential following action potentials. These effects recovered over a 1-s period. The study suggests that a brief electric field induces a prolonged suppression of epileptiform activity, which can be related to changes in neuronal membrane properties, including attenuation of signals depending on the persisting Na(+) current.

Subthreshold activation of spinal motoneurones in the stretch reflex: experimental data and modeling

Responses of gastrocnemius-soleus motoneurones to stretches of the homonymous muscles were recorded intrasomatically in decerebrate cats; changes of membrane potential (MP) were evoked by smoothed trapezoid stretches of the muscles. Amplitudes of separate excitatory postsynaptic potentials (EPSPs) were defined via differences between values of MP at the end and beginning of the positive derivative waves, which were also used as basic elements in the model of the excitatory postsynaptic currents (EPSCs). EPSCs were assumed to be transformed into EPSPs by low-pass filtering properties of the somatic membrane; parameters of the filtering were firstly defined from analysis of Ia EPSP in the same cell and then were applied in model P ( m0). The model showed unsatisfactory quality in tracking slow components of MP; to overcome the disadvantage there was proposed model P ( m1) based on addition to P ( m0) the difference between two low-pass filtered signals MP and P ( m0) (the cutoff frequency 10 or 20 Hz). An overestimation of EPSPs' amplitudes was corrected in model P ( m2). The mismatch in tracking slow changes of MP was assumed to be connected with summation of a great number of low-amplitude EPSPs generated at distal dendrites; information about waveform of separate EPSPs could disappear in this process. One can speculate that slow components of membrane depolarization at least partly are linked with the persistent inward currents in dendrites; variable and, sometimes, too fast decays in EPSPs seem to reflect inhibitory synaptic influences.

Diagnosis of the irritable colon: manometric and myoelectric investigations (author's transl)

Manometric investigations of patients with irritable colon show an undisturbed cyclic course of interdigestive motility studies of the rectosigmoid in patients with irritable colon show a spectrum of variable frequency of slow membrane potential changes with predominance of a frequency of 3/min. In addition, after a 1000 calorie test meal, patients with irritable colon showed a significantly prolonged increase of motility. As functional disturbances of irritable colon are mainly diagnosed by exclusion of organic changes, further development and rational use of colonic myoelectric methods promises future possibilities for objective diagnosis and control of treatment.

Voltage-clamp-controlled current-clamp recordings from neurons: an electrophysiological technique enabling the detection of fast potential changes at preset holding potentials.

Investigations of the properties of fast, transient potential changes (e.g. receptor potentials or synaptic potentials) in excitable cells by means of current-clamp recording techniques require the exact adjustment and control of membrane potentials. Usually, the desired membrane potential values are set by current injection via the recording electrode and are controlled manually by regulating the current strength necessary to maintain a constant potential. However, this technique is associated with a number of disadvantages. A single-electrode current- and voltage-clamp amplifier was therefore modified to compensate for slow membrane potential changes without affecting faster voltage responses. Basically, low-pass filters with selectable time constants were incorporated into the voltage-clamp feedback circuit to control the amplifier's response speed. In addition, the amplifier's electronic circuits were altered to enable current pulse injection into the cells. Thus, while recording at preset and controlled membrane potentials, it was possible to monitor the cell's input resistance or current/voltage relationship. This new recording technique has been designated "voltage-clamp-controlled current clamp" (VCcCC) and its performance was tested by intracellular recordings from neocortical and neostriatal neurons in vitro using either conventional microelectrodes or patch-clamp electrodes.

Non-cholinergic excitatory and inhibitory junction potentials in the circular smooth muscle of the guinea-pig ileum.

Intracellular micro-electrodes have been used to record evoked non-cholinergic junction potentials from the muscle layers of strips of guinea-pig ileum cut parallel to the longitudinal muscle. Transmural stimulation with single pulses, 0.6 ms duration produced inhibitory junction potentials (i.j.p.s) in the circular muscle layer. In the circular muscle layer, transmural stimulation with repetitive volleys (e.g. three pulses, 0.6 ms, 50 Hz delivered every 4 s) at low stimulus strengths (25-40 mA) produced non-cholinergic excitatory junction potentials (e.j.p.s) after an initial i.j.p. At higher stimulus strengths (greater than 40 mA) i.j.p.s occurred following each volley but were superimposed on a prolonged depolarization. Following repetitive volley stimulation every four seconds in the presence of apamin (0.25 microM), the i.j.p.s. were abolished and the non-cholinergic e.j.p.s clearly showed facilitation. At higher stimulus strengths (and at volley repetition rates of less than 0.1 Hz) volley stimulation now produced an apamin-resistant slow hyperpolarization followed by a distinct slow depolarization. Electrotonic potentials were readily recorded from the superficially located longitudinal muscle cells: in this muscle layer transmural stimulation produced small, slow changes in membrane potential. These results suggest that non-cholinergic excitatory and inhibitory nerve fibres primarily supply the circular rather than the longitudinal muscle layer in the guinea-pig ileum.

Calcium‐dependent inward current in Aplysia bursting pace‐maker neurones.

Depolarizing voltage-clamp pulses elicit a triphasic series of tail currents (phase I, II and III) in Aplysia burst-firing neurones L2-L6. The sequence and time course of the tail currents resemble slow changes in membrane potential which follow bursts in the unclamped cell. The phase II tail current is an inward current with a time course similar to that of the depolarizing after-potential (d.a.p.) which follows bursts in the unclamped cell. The phase II tail current is suppressed by depolarizing pulses which approach ECa, is blocked by Ca2+ current antagonists (Co2+ and Mn2+), and is blocked by intracellular injection of EGTA. The phase II tail current is not blocked by agents which block Na+-dependent action potentials, the Na+-Ca2+ exchange pump, or the Na+-K+ exchange pump. The phase II tail current is not blocked by the elimination of large outward K+ currents which can lead to extracellular K+ accumulation. Thus, the phase II tail current is not generated by any of these processes. The phase II tail current is reduced by about 60% following substitution of tetramethylammonium (TMA+) for external Na+, but is unaffected by reducing external Cl-. The phase II tail current is distinct from a persistent inward Ca2+ current which underlies the negative resistance region of the steady-state current--voltage relation of bursting cells. The persistent inward current is only slightly reduced by TMA+ substitution for Na+, and is enhanced by EGTA injection. Injection of Ca2+ into Aplysia bursting cells elicits a biphasic (inward-outward) current. The inward current can be observed in isolation after blocking the outward component (Ca2+-activated K+ current) with 50 mM-external tetraethylammonium. The Ca2+-elicited inward current has a reversal potential near -22 mV, and is non-selective for Na+, K+ and Ca2+. The reversal potential is unaffected by changes in Cl- and pH. The Ca2+- activated conductance is apparently voltage independent. We propose that the phase II tail current, and hence the d.a.p., is due to the Ca2+-dependent activation of a voltage-independent non-specific cationic conductance. This conductance participates in generating the depolarizing phase of bursting pace-maker activity.

Slow potential changes in mammalian muscle fibers during prolonged hyperpolarization: transport number effects and chloride depletion.

Mammalian skeletal muscle fibers exhibit large slow changes in membrane potential when hyperpolarized in standard chloride solutions. These large slow potential changes are radically reduced in low chloride solutions, where the faster and smaller potential change ("creep"), usually observed in amphibian fibers, becomes apparent. The slow potential change during a hyperpolarizing current pulse leads to an increase in apparent resistance of up to nine times the instantaneous value and takes minutes to reach a steady value. It then takes a similar time to decay very slowly back to the resting membrane potential after the current pulse. The halftime for the slow potential change was found to be inversely proportional to the current magnitude. From measurements of immediate post-pulse membrane potentials, assuming constant ionic permeabilities, the internal chloride concentration was calculated to decrease exponentially towards a steady value (e.g., for one fiber from 12.3 to 6.6 mM after a 330-sec pulse). The time course and magnitude of the concentration change were predicted from chloride transport number differences, and the known and measured properties of the fibers, and were found to agree very well with the values obtained from experimental measurements. In addition, the shapes of the V2-V1 responses, measured in the three-electrode current clamp set-up with either potassium chloride or potassium citrate current electrodes, were as predicted by transport number chloride depletion effects and were at variance with the predictions of a permeability change mechanism.

Alpha and beta-adrenergic mediation of membrane potential changes and metabolism in rat brown adipose tissue.

Membrane potential and flavoprotein redox state have been measured simultaneously and continuously in brown adipose tissue in order to determine how nerve stimulation and adrenergic agonists control its metabolic activity. Both trains of nerve impulses and addition of noradrenaline evoke two temporally distinct cell depolarizations. The first rapid depolarization precedes the increase in flavoprotein reduction. With nerve stimulation, at the time of maximum flavoprotein reduction the cell has repolarized or hyperpolarized. The second slow depolarization follows flavoprotein reduction. Phentolamine, an alpha antagonist, selectively blocks the first depolarization, but not the flavoprotein reduction. However the time of maximum flavoprotein reduction is delayed. Propranolol, a beta antagonist, delays the first repolarization until the end of nerve stimulation and inhibits the transient hyperpolarization, second depolarization and flavoprotein reduction. Isoproterenol, a beta agonist, or the fatty acid octanoate produce only a transient hyperpolarization and subsequent slow depolarization following flavoprotein reduction. Thus brown adipose tissue contains both alpha- and beta-adrenergic receptors. Stimulation of alpha receptors produces an early membrane depolarization. Stimulation of beta receptors leads to an increase in metabolic activity which then appears to produce slow changes in membrane potential.

Two levels of resting potential in canine cardiac Purkinje fibers exposed to sodium-free solutions.

Canine cardiac Purkinje fibers exposed to sodium-free solutions containing 16 mM CaCl2, 20 mM tetraethylammonium chloride, 108 mM tetramethylammonium chloride, and 2.7 mM KCl may be quiescent at a resting potential of either -50 mV or -90 mV. The membrane potential of these fibers can be switched from -50 mV to -90 mV by a hyperpolarizing current pulse and from -90 mV to -50 mV by a depolarizing current pulse. The transition from -50 mV to -90 mV depends on a voltage-dependent increase in potassium conductance, that conductance being low at -50 mV and high at -90 mV. A reduction in potassium conductance causes the fiber to depolarize from -90 mV to -50 mV because of the presence of an inward current which apparently is carried mainly by Ca. Fibers that show a high resting potential cannot be excited except by depolarizing stimuli strong enough to move the membrane from -90 mV to a threshold potential of about -40 mV. Fibers that show a low resting potential are more easily excited and may show rhythmic activity sustained by afterpotentials that appear only if the low membrane potential is accompanied by a low potassium conductance. Slow changes in membrane potential also are seen; these changes may result from movements of chloride.

Transmission without spikes between locust interneurones and motoneurones

MANY neurones, particularly in sensory systems of both vertebrates and invertebrates, do not produce action potentials1–3. In motor pathways within the central nervous system of arthropods there are interneurones whose slow changes in membrane potential can affect the frequency of action potentials in motoneurones4–6. Some of these interneurones normally produce spikes6, but others apparently do not4,5. We have studied the properties of synaptic transmission between these non-spiking interneurones and motoneurones in the locust, Schistocera gregaria, in the course of investigating the integrative mechanisms underlying the generation of motor patterns7.

Activity in Single Hippocampal Pyramids

AbstractEuler, C. V. and J. D. Green. Activity in single hippocampal Pyramids.Activity from single pyramidal cells of dorsal hippocampus has been studied in rabbits under light urethane anaesthesia or with encéphale isolé. Capillary microelectrodes were used for recording. Respiratory and cardiovascular movements of the brain were reduced by using a ‘closed system’. Extracellular biphasic positive‐negative spikes of large amplitude were frequently recorded. The shape of the extracellular spikes indicate that the soma spikes are usually not followed by excitation of the dendritic membrane. However, occasionally spikes with negative‐positive potential sequence indicating somatofugal excitation of the dendrites, have been recorded after a burst of positive‐negative spikes. This occurred in response to prolonged repetitive stimulation and in after‐discharges. Spikes were normally not recorded in the dendritic layer. Repetitive stimulation, however, elicited sharp spikes in the apical dendrites increasing in number and amplitude with increasing stimulus strength and duration.Action potentials and slow changes in membrane potential were commonly recorded with big attenuation but without other signs of serious injury.Polarizing hippocampal neurones with minute currents in the order of 2 × 10‐9A through the recording microelectrode stimulated or inhibited that cell from which the activity was extracellularly recorded.The hippocampus is an uncomplicated cortical structure with a relative uniform and simple lamination. These and other features make the Ammon's horn a suitable site for studies of cortical properties (see e. g. Euler, Green and Ricci 1958). This paper presents an analysis of the spontaneous activity in single hippocampal pyramids and a component analysis of spike potentials recorded extracellularly. A subsequent paper (Euler and Green 1960) deals with the activity patterns which can be elicited through afferent stimulation. A ‘positive’ wave with rapidly declining ‘positive’ spikes proved to be a pattern entity of possible significance for the ‘brain waves’ of the hippocampus. Although no successful intracellular records of this phenomenon were obtained, the experimental data presented in the present paper lend themselves to the conclusion that the spikes and the wave originate in the same neurone and that the phenomenon thus may be identified as the ‘inactivating process’ of Granit and Phillips (1956).

Kinetics of slow changes in membrane potential induced by direct current polarization of single nerve fibers.

A direct current pulse applied to an isolated single fiber of the frog sciatic induces a slow drift in membrane potential which can be described by a single exponential term throughout most of its time course. Both magnitude and time parameter are functions of pre-existent membrane potential. With increasing cathodal polarization the magnitude of the drift approaches a limiting value which is dependent only on the duration of the polarizing pulse. No change in resistance is detectable with brief test transient pulses. In fibers sufficiently hyperpolarized to minimize sodium inactivation it is observed that impulses fired off at any time during the course of the slow potential drift are characterized by identical peak values of membrane potential. This indicates that active firing results in a short circuiting of the mechanism responsible for the slow drift. Whereas the data presented favor a change in some e.m.f. as responsible for the slow drift, there exists strong evidence that the potassium emf remains constant.

Slow membrane potential changes accompanying excitation and inhibition in spinal moto- and interneurons in the cat during natural activation.

Summary.Slow membrane potential changes accompanying excitation and inhibition processes have been studied in spinal moto‐ and inter‐neurons of spinal cats, using intracellular recording technique.Section I. Long‐lasting shifts in membrane potential level have been recorded in both moto‐ and interneurons during sustained rhythmical activity.A closer study of the slow membrane potential changes and their relation to spike potentials has revealed fundamentally similar events in moto‐ and interneurons; the quantitative analyses have mainly been performed on niotoneurons whose steady membrane potentials allow of studies for sufficiently long periods. Special attention has been given to the slow membrane potential oscillations during rhythmical firing.The firing level for the onset of rhythmical spike discharges was found to be relatively constant in one and the same neuron; with increase in discharge frequency a definite lowering of the firing level occurs, an approximately linear relation being found to exist between firing level and impulse interval.During periods of regular rhythmical firing subthreshold membrane potential oscillations may occasionally he seen associated with spikes of reduced amplitude or not accompanied by any recordable spikes.The potential analysis has led to a tentative differentiation between an initial quick and a later slow phase of repolarization. The quick repolarization level, more or less marked in different neurons, is of approximately the same value during natural activation and single ortho‐ or antidromic stimulation; it varies within relatively narrow limits during the large natural variations in membrane potential observed in the experiments.The slow repolarization level, which may show great variations even at one and the same membrane potential level, undergoes a pronounced reduction with increasing frequency of the rhythmical activity. The relation hetween the slow repolarization level and the impulse interval is found to be approximately linear.The typical variations in quick and slow membrane processes during various activity levels of a motoneuron have been diagrammatically represented. The possibility is discussed that the quick spike processes and slow potential variations represent changes in different membrane potential fractions, analogous to the Q‐ and L‐fractions established in peripheral nerve.The evidences in favour of an inherent oscillation mechanism in the inembrane activated at a critical level of depolarization and primarily responsible for the discharge frequency are discussed.Section II. Membrane potential changes during inhibition have been studied in moto‐ and interneurons using exteroceptive inhibitory stimulation. In both types of neurons natural activation of inhihitory sources resulted in a slow repolarization not exceeding the highest membrane potential recorded in the absence of excitatory stimulation.The inhibitory effects of synchronized afferent volleys have been analysed in motoneurons in different states of rhythmical activity. The amplitude of the repolarization dip produced by each afferent volley was found to depend on the membrane potential level at the onset of inhibition. During repetitive stimulation a steady state was gradually attained, the level of which varied with the initial state of activity of the neuron.Section III. Both in moto‐ and interneurons the occurrence of random miniature potentials of varying amplitude has been demonstrated, those of larger amplitude (10 mV) apparently being built up out of the smaller “unitary potentials” of 1–3 mV.Increase as well as decrease of the miniature potential activity could be produced by natural activation of extero‐ or proprioceptive sources influencing the neuron. Correlations to the membrane potential level showed a reduced amplitude range of miniature potentials during increased membrane potential.In addition to the most common type of miniature potentials representing an inside positive change, potentials of the opposite sign were occasionally observed. The functional role of such randomly occurring repolarization potentials has been exemplified and a comparison made with similar phenomena observed in other types of nerve cells.