Values Of Membrane Potential Research Articles

Effect of hemodilution, hemoconcentration and beta-adrenergic stimulation on the blood flow and membrane potential value of the liver.

The hyperpolarization produced by isoproterenol is concurrent with an increased blood flow through the isolated dog liver. This observation suggested a relationship between membrane potential (MP) and

A model for phasic and tonic repetitively firing neuronal encoders.

A model for neuronal encoders is presented. Its mathematical description consists of two coupled first order, non-linear differential equations giving the time course of the membrane potential and of a leak function under conditions of continuous drive. The leak function is given by the ratio of the transmembrane conductance to the effective encoder capacitance and is closely tied to the Hodgkin-Huxley results on the behavior of gK and gNa. Since neuronal impulse encoding does not in general proceed in a space clamped region, the values of membrane potential and “leak” entering the differential equations are those at the trigger zone. The effects of electrotonic spread are then incorporated in the leak function. A particularly simple two parameter form of the model is explicitly written. By changing the value of one of the parameters the properties of the model change from that of exhibiting all features of rapid adaptation to those of tonic repetitive firing. Predictions of the model are discussed, as is the relationship between properties of the model and features of voltage clamp data.

Correlation between membrane potential, cell shape, and motile activity in Amoeba proteus

The various motile activities and cell shapes of Amoeba proteus grown in Chalkley's solution are correlated with definitive electrical membrane potentials. The same correlations were found when definitive motile activities and cell shapes were experimentally induced by changing the pH of the culture medium. The highest values of membrane potential (−70 mV) were measured in monopodial amebae during active locomotion. In resting cells, which prevail in acid or basic media, the membrane potential decreases to −5 mV. In those resting cells, which also stop internal cytoplasmic movement at basic pH, the membrane potential turns positive (+9 mV − +30 mV).

Lanthanum-induced alterations in cellular electrolytes and membrane potential in Ehrlich ascites tumor cells.

AbstractWe have investigated the effect of varying La+3 concentrations (0.01 mM to 2.0 mM) on membrane potential and electrolyte composition of Ehrlich ascites tumor cells. La+3 concentrations less than 0.02 mM had no effect. Above 0.02 mM, La+3 induced concentration‐dependent loss of electrolytes and water from the cells. At 1.0 mM the effect was maximal and resulted in an 87% reduction in cellular K+, 79% in Cl− and 21% in Na+ within 4.8 minutes. The Na+ loss occurred even in the face of an electrochemical potential gradient favoring Na+ entry. La+3 increased the recorded values of membrane potential; the magnitude of the effect was related to the external La+3 concentration, and was maximal at 1.0 mM. Studies using 140La showed that La+3 binds rapidly to the cell surface and does not enter the cells. The amount of La+3 bound to the cells was related to the external La+3 concentration by a sigmoidal curve and was maximal at about 1.0 mM. The bound La+3 could not be displaced by either added La+3 or Ca+2. Agents known to effect the integrity of the cell membrane, such as phospholipase C, neuraminidase, pronase and Hg+2 were tested for their ability to displace bound La+3. Only pronase displaced bound La+3, indicating that La+3 associates with cell protein. It is hypothesized that La+3 rapidly interacts with membrane protein causing alterations in membrane permeability and capacity to actively transport ions.

Activation of the electrogenic sodium pump in guinea-pig auricles by internal sodium ions.

1. The effect of various intracellular Na concentrations ([Na](i)) on the membrane potential after hypothermia was studied in guinea-pig auricles.2. For varying [Na](i), the atria were cooled for 4 hr at 4-6 degrees C in a K-poor solution with different concentrations of NaCl. The auricles were rewarmed in normal Tyrode solution at 35 degrees C.3. Extracellular space (ECS), intracellular Na and K concentrations ([Na](i) and [K](i)) and membrane potential of the atria were measured before and after hypothermia.4. The ECS, measured as inulin space, amounted to 350 ml./kg wet wt. at 35 degrees C and to 300 ml./kg wet wt. at 4-6 degrees C.5. [K](i) decreased during cooling and increased during rewarming the auricles. [Na](i) increased during hypothermia in bathing fluids containing NaCl, but decreased in NaCl- and Na-free solutions. At the beginning of rewarming a net Na transport occurred from cells with high [Na](i), while a net Na uptake took place in atria with low [Na](i).6. At the same time, the membrane potential of auricles with increased [Na](i) hyperpolarized beyond the steady-state value recorded at the end of rewarming, or even beyond the calculated K(+) equilibrium potential (E(K)). Afterwards, the hyperpolarization levelled off, while the E(K) values increased further. The membrane potential of atria with decreased [Na](i) showed no transitory hyperpolarization during rewarming.7. The hyperpolarization beyond the steady-state value of membrane potential in rewarmed auricles was significantly correlated to the active Na efflux.8. From these results it is concluded that the membrane potential of guinea-pig atria after hypothermia is affected by an active, electrogenic Na pump activated by intracellular Na ions.

Direct measurements of membrane potential and membrane resistance of human red cells.

1. In order to evaluate the membrane potentials calculated from the distribution of chloride ions in human red cells and plasma, it is desirable to have a direct measurement of the transmembrane potential of these cells.2. A method has been devised for introducing a capillary micro-electrode into human red cells. The method allows simultaneous measurements of potential and membrane resistance with only one micro-electrode located in the cell.3. Upon impalement of single cells in plasma, a scatter of membrane potentials and of resistance values was obtained. The potential drop never exceeded -14 mV and the maximum resistances were about 7 Omega. cm(2). Positive potentials were obtained on impalement of red cell aggregates.4. Arguments are given to support the view that it is in these cells which suffer least damage from the impalement that maximum values of membrane potentials and resistances are observed. The errors caused by the change in the liquid junction during the impalement have been estimated.5. As judged from this study, it seems permissible under normal conditions to calculate the membrane potential of the red cell from the chloride concentrations in plasma and in intracellular water.

Cardiac myofibrillar ATPase activity in hypophysectomized or thyroidectomized rats

We have examined the influence of chronic in vivo alterations of thyroxine levels on the electrophysiological and mechanical properties of rabbit ventricular papillary muscles measured in vitro. Marked changes in the repolarization phase of the action potential and the time to peak tension of isometric twitches were observed, when thyroid hormone levels were increased above or decreased below normal. The time to peak tension was consistently shorter than normal in hyperthyroid and longer than normal in hypothyroid preparations. In hypothyroid preparations the action potential duration was greater than that of controls at all stimulation frequencies tested (0.1 to 1.0 Hz). In hyperthyroid preparations, the repolarization phase consisted of an initial phase of fast repolarization to membrane potential values between −20 and−40 mV followed by a plateau The early phase of repolarization persisted at all stimulation frequencies tested (0.1 to 1.0 Hz) but the plateau component increased markedly as the stimulation frequency was decresed. The early phase of repolarization was markedly reduced in the presence of 4-aminopyridine. These reults suggest that thyroxine levels may modulate the kinetics of a transient outward current which in rabbit papillary muscle normally is responsible for the frequency dependence of action potential duration. Action potential amplitude, maximum rate of rise resting membrane potential and peak isometric twitch tension were not markedly different between the three classes of preparations. A second depolarizing response occurred in all hyperthyroid preparations at low stimulation frequencies (0.1 to 0.4 Hz) but not in control or hypothyroid preparations. This second depolarizing response, which was eliminated by D-600 treatment, was similar to the calcium-dependent slow action potentials recorded in other cardiac preparations. These two component action potentials could represent either tials recorded in other cardiac preparations. These two component action potentials could represent either intrinsic single cell activity, or a re-entry wave of depolarization which results from nonhomogeneous excitation.

A study of the crustacean axon repetitive response. II. The effect of cations, sodium, calcium (magnesium), potassium and hydrogen (pH) in the external medium.

AbstractThe effects of sodium, calcium, potassium (magnesium), potassium, and hydrogen (pH) ion concentration in the external medium on the repetitive response and the transmembrane electrical parameters of the crustacean axon have been investigated. (1) The action potential is reduced with decrease in sodium ion concentration, the relationship is linear if the spike voltage is plotted against the log (Na0). The action potential amplitude does not increase significantly, above 135 mv, attained at Na0 = 452 mM, if Na0 is increased. (2) The repetitive response and oscillatory activity in general disappears as the sodium concentration is reduced to less than 150 mM. (3) The critical firing level increases with decrease in sodium, the relationship linear with respect to log (Nao). (4) The positive after potential amplitude is not affected by the sodium concentration. (5) The membrane resistance is not affected by sodium concentration. (6) Calcium lack results in decreased critical firing level and spontaneous firing, followed by a total and irreversible loss of excitability. The membrane resistance is markedly decreased. Polarizing current, if applied early after the onset of the calcium lack effect, may restore, at least partially, the excitability phenomenon. (7) Calcium excess increases membrane resistance, depresses excitability. Calcium concentration of 150 mM abolishes the repetitive response. (8) There is a 3.3+: 1 ratio Na:Ca for threshold level of repetitive response. Lower ratio figures, by reducing Na or increasing Ca or both, eliminates repetition. Increasing the ratio figure by increasing sodium or decreasing calcium or both augments oscillatory activity. This ratio is constant between the limits 400 mM Na:125, Ca to 90 mM Na:25 mM Ca. (9) Magnesium may substitute for calcium, the Na:Mg ratio for repetitive response threshold is 3.3:2. (10) Repetitive firing may be elicited over a wide range of pH values 4.2–10.5; membrane potential and resistance values decline invariably at pH values above 9.5 and below 4.5. (11) Repetitive firing is enhanced by increasing pH values, depressed by reducing pH values. (12) Effect of excess potassium produces depolarization, reduced membrane resistance, inactivation and abolition of repetitive firing, may be relieved by applied hyperpolarization. (13) Potassium lack results in membrane potential and resistance irreversible decline, permanent inactivation, total loss of excitability. Partial restoration by strong hyperpolarization if applied before effect is complete. Potassium replacement in solution only slows or temporarily arrests the overall membrane deterioration. (14) Conclusions ‐ sodium controls spike, potassium controls after potential, calcium (magnesium) controls membrane permeability, pH controls amount of available ionized calcium. Repetitive firing requires proper ratio 3.3/1 of (Nao)/(Ca0), pH above 7.6 and potassium at 15 mM in solution.

Sodium influx and excitation in uterine smooth muscle.

THE applicability of the ionic hypothesis of excitation, more specifically the transient increase of sodium permeability during an action potential1, has not been extended to smooth muscles in general. This is due largely to serious technical difficulties in impaling the small cells of smooth muscles, as shown by the comparatively low and widely variable values of membrane potentials for smooth muscles. Direct tests of the effect of sodium deprivation on the action potential are therefore rather difficult to make. Additional confusion has been caused by claims that action potentials persist in media containing very little sodium2 or no sodium at all3.

Effects of ethanol on the membrane potential and membrane resistance of frog muscle fibres.

AbstractThe effects of ethanol on the membrane potential and membrane resistance of frog muscle fibres in vitro were studied by means of intracellular microelectrode technique. By continuous recording of the membrane potential level from one fibre, as well as by consecutive recordings from different fibres, the time course of the potential changes induced by different concentrations of ethanol was followed for periods of up to one hour. At the lowest concentrations used, 0.05 and 0.1 M, a depolarization, although slow and sometimes irregular, could usually be demonstrated. At a concentration equal to or higher than 0.2 M, a marked lowering of the membrane potential value was regularly observed. The depolarization rate increased with higher ethanol content, a typical result being a 15 per cent reduction of the initial membrane potential value after 15 min of exposure to 1.0 M ethanol. Reversal of the membrane potential changes after the ethanol had been washed out from the muscle bath was also demonstrated. Determinations of the voltage‐current relation of the muscle fibre, either by square pulse analysis or by direct recording of voltage‐current curves, revealed a gradual lowering of the membrane resistance, the effect increasing with the ethanol concentration from 0.2 to 1.0 M; at lower concentrations the changes in membrane resistance were within the normal variations found in untreated muscle.

Influence of asphyxia on membrane potential level and action potentials of spinal motoand interneurons.

AbstractKolmodin, G. M. and C. R. Skoglund. Influence of asphyxia on membrane potential level and action potentials of spinal moto‐ and interneurons. Acta physiol. scand. 1959. 45. 1–18. — Asphyxial changes in spinal moto‐ and interneurons of decapitate cats were studied by means of intracellular microelectrodes. In both types of neurons the first change in membrane potential was usually observed after about 30 sec in the form of a depolarization of 5–10 mV which after some 30 sec was followed by a phase of more rapidly developing depolarization of larger amplitude; during recovery a phase of increased polarization may be observed. Interneurons showed signs of being more resistant to asphyxia than moto‐neurons. The spib potential underwent a. successive diminution in amplitude, at first owing to the decrease in membrane potential value, later also due to a change in spike peak level. During the later stage of asphyxia a decrease of both the rate of rise of the ascending and the rate of decay of the descending spike phases could be demonstrated. Rhythmical interneuron discharges showed periods of increased and decreased frequency before final blocking.

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.

Membrane and action potentials of spinal interneurons in the cat.

Summary.Intracellular recordings have been performed from interneurons in the lumbar segments of the spinal cord of non‐anesthetized spinal cats. A full account is given of the experimental technique used in this and other investigations in the same series.Section I. Continuous inkwriter recordings of the membrane potential level obtained from interneurons in various parts of the cord cross section are presented and compared with records from afferent fibres and motoneurons. Data of the average amplitude values and recording times for the different types of units are given.Various factors influencing the values of the recorded membrane potential are discussed and an attempt has been made to find a relation hetween the degree of injury, cell size and recorded membrane potential.Section II. The most common types of interneuron discharges in response to synchronous afferent volleys are described and typical variations in prepotential configuration are illustrated.The firing level at which an impulse is set up by afferent single shock stiniulation has been analysed in some detail in an experiment in which physiological variations in the membrane potential level were induced by natural sensory stimulation. It was found that the firing level is not constant but is reduced with lowering of the membrane potential value in an approximately linear way.The spike repolarization level was also found to vary with the nienibrane potential level in a similar way which may result in levels of increased or decreased polarization as compared with the pre‐spike level.Records of spontaneous and naturally induced activity are presented showing the relation between slow depolarization processes and spike discharges.In experiments including both natural and artificial activation records have been obtained showing no distinct prepotentials. In such recordings the spikes have usually been of short duration (average 0.8 msec as compared with 1.3 msec for spikes accompanied by slow potentials). Some of these cases may represent axon recordings, but possible explanations of an absence of recordable prepotentials from soma are also discussed.In the majority of interneuron recordings the spike amplitude has been 10–20 per cent lower than the membrane potential value; overshooting has only been observed in about 10 per cent of the recordings. Some factors influencing the spike amplitude have been taken up for discussion.Special attention has been given to variations in spike configuration in the form of pronounced notches and a splitting up into sub‐spikes; these variations have been interpreted as signs of a fractionated function of the cell membrane.