Some bio-electric parameters of early Xenopus embryos

Development ◽  
1970 ◽  
Vol 24 (3) ◽  
pp. 535-553
Author(s):  
J. F. Palmer ◽  
Christine Slack
Keyword(s):  
Membrane Potential ◽  
South African ◽  
Developmental Stages ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Mean Value ◽  
Cell Junctions ◽  
Current Spread ◽  
Intracellular Microelectrodes ◽  
Junctional Resistance

Membrane potential and resistance were measured in eggs, cleavage stages and blastulae of the South African toad Xenopus laevis, using intracellular microelectrodes. The membrane potential increased from −6·5 ± 2mV in eggs to −57 ± 8·0mV at the mid-blastula stage. The input resistance of fertile eggs ranged from 0·5 MΩ to 5·0 MΩ corresponding to a specific resistance of 20–200kΩcm2. During the first two or three division cycles the input resistance usually decreased by a factor of 2–10 and then subsequently rose during the blastula stages from a mean value of 600 ± 100kΩ at stage 5 to 2·0 ± 0·5 MΩ at stage 8. At all developmental stages examined, point polarization of a surface cell in the embryo by rectangular current pulses of 0·5−6 × 10−8 A produced voltage deflexions in other surface cells. This was seen even when several (7–8) cell junctions intervened between the current passing and voltage recording microelectrodes at distances of more than 1 mm. These measurements suggest that the junctional resistance is low compared with that at the surface, though the geometrical arrangement of cells is not favourable for calculation of absolute values of membrane resistance. Current spread between cells occurred apparently less easily during mid-blastula stages than at earlier stages in development, perhaps indicating an increase in junctional resistance during development. A comparison has been drawn between the present measurements and similar ones made in another amphibian, Triturus.

Role of Potassium Conductances in Determining Input Resistance of Developing Brain Stem Motoneurons

2000 ◽  
Vol 84 (5) ◽  
pp. 2330-2339 ◽  
Author(s):  
William E. Cameron ◽  
Pedro A. Núñez-Abades ◽  
Ilan A. Kerman ◽  
Tracy M. Hodgson
Keyword(s):  
Membrane Potential ◽  
Brain Stem ◽  
Barium Chloride ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Electrode Recording ◽  
Percent Increase ◽  
Potassium Conductances ◽  
Brain Stem Slices

The role of potassium conductances in determining input resistance was studied in 166 genioglossal (GG) motoneurons using sharp electrode recording in brain stem slices of the rats aged 5–7 days, 13–15 days, and 19–24 days postnatal ( P). A high magnesium (Mg2+; 6 mM) perfusate was used to block calcium-mediated synaptic release while intracellular or extracellular cesium (Cs+) and/or extracellular tetraethylammonium (TEA) or barium (Ba2+) were used to block potassium conductances. In all cases, the addition of TEA to the high Mg2+ perfusate generated a larger increase in both input resistance ( R n) and the first membrane time constant (τ0) than did high Mg2+ alone indicating a substantial nonsynaptic contribution to input resistance. With intracellular injection of Cs+, GG motoneurons with lower resistance (<40 MΩ), on the average, showed a larger percent increase in R n than cells with higher resistance (>40 MΩ). There was also a significant increase in the effect of internal Cs+ on R n and τ0 with age. The largest percent increase (67%) in the τ0 due to intracellular Cs+ occurred at P13–15, a developmental stage characterized by a large reduction in specific membrane resistance. Addition of external Cs+blocked conductances (further increasing R n and τ0) beyond those blocked by the TEA perfusate. Substitution of external calcium with 2 mM barium chloride produced a significant increase in both R n and τ0at all ages studied. The addition of either intracellular Cs+ or extracellular Ba2+created a depolarization shift of the membrane potential. The amount of injected current required to maintain the membrane potential was negatively correlated with the control R n of the cell at most ages. Thus low resistance cells had, on the average, more Cs+- and Ba2+-sensitive channels than their high resistance counterparts. There was also a disproportionately larger percent increase in τ0 as compared with R n for both internal Cs+ and external Ba2+. Based on a model by Redman and colleagues, it might be suggested that the majority of these potassium conductances underlying membrane resistance are initially located in the distal dendrites but become more uniformly distributed over the motoneuron surface in the oldest animals.

scholarly journals Membrane Potential of Brown Adipose Tissue

1968 ◽  
Vol 52 (6) ◽  
pp. 925-940 ◽  
Author(s):  
L. Girardier ◽  
J. Seydoux ◽  
T. Clausen
Keyword(s):  
Adipose Tissue ◽  
Membrane Potential ◽  
Brown Adipose Tissue ◽  
Membrane Resistance ◽  
Mean Value ◽  
Extracellular Potassium ◽  
Bicarbonate Buffer ◽  
Interscapular Brown Adipose Tissue ◽  
Extracellular Potassium Concentration ◽  
Brown Adipose

Membrane potentials were recorded in isolated segments of interscapular brown adipose tissue from rats. After equilibration at 29°C in Krebs-Ringer bicarbonate buffer a mean value of -51 ± 4 mv (SD) was found. This level could be maintained for up to 5 hr. The mean effective membrane resistance was 1.35 ± 0.45 megohm. The membrane potential was a function of the extracellular potassium concentration. Ouabain (10-6-10-3 M) and incubation in K-free buffer produced progressive depolarization. Epinephrine and norepinephrine in concentrations as low as 10-8 g/ml produced a prompt depolarization. Cooling of the tissue and lowering of the oxygen tension caused a marked and reversible decrease in the membrane potential. In tissue obtained from cold-adapted rats, the membrane potential was considerably diminished. 6Assuming that the membrane potential is some function of the Na permeability of the plasma membrane it is suggested that an increase in the rate of active Na-K transport and ensuing ADP formation might contribute to the increase in respiration seen during exposure to thermogenic stimuli.

Electrical properties of phrenic motoneurons in the cat: correlation with inspiratory drive

1987 ◽  
Vol 58 (1) ◽  
pp. 105-124 ◽  
Author(s):  
J. S. Jodkowski ◽  
F. Viana ◽  
T. E. Dick ◽  
A. J. Berger
Keyword(s):  
Membrane Potential ◽  
Electrical Properties ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Mean Value ◽  
Resting Membrane Potential ◽  
Mean Values ◽  
Phrenic Motoneurons ◽  
The Mean ◽  
Potential Level

1. Resting membrane potential (Vmp), input resistance (Rn), rheobase (Irh), and after hyperpolarization duration (AHPdur) and amplitude (AHPamp) were measured in 38 phrenic motoneurons of anesthetized, paralyzed, and artificially ventilated cats during hypocapnic apnea. The mean +/- SD and range of values for these variables were as follows: Vmp, -68 +/- 5mV (range: -60 to -82); Rn, 1.3 +/- 0.6 M omega (0.6-2.4); Irh, 9.7 +/- 5 nA (2-20); AHPdur, 68 +/- 19 ms (37-134); AHPamp, 3.3 +/- 1.8 mV (1.0-8.5). In 31 motoneurons, the membrane potential level at which firing occurred (Vthr) during intracellular current injection was measured. The mean value of Vthr was -58 +/- 3 mV (range: -52 to -64). 2. A histogram of Rn revealed a bimodal distribution. Also a plot of Irh against Rn showed a grouping of the motoneurons into two subpopulations: 1) low-Rn and high-Irh cells, called type L neurons, and 2) high-Rn, low-Irh cells, called type H neurons. The overall negative linear correlation between Irh and Rn (r = -0.85; P less than 0.0001) resulted from this grouping rather than from a strictly linear relation between these two variables. 3. Electrical properties were compared for type L (n = 20) and type H (n = 18) phrenic motoneurons. The following mean values were found for each group, respectively: Rn, 0.8 and 1.8 M omega; Irh, 13.7 and 5.3 nA; AHPdur, 58 and 79 ms; AHPamp, 2.4 and 4.4 mV. All differences were significant (t test, P less than 0.001). Mean Vthr was the same for the two groups. 4. Comparison of these data with those available for lumbosacral motoneurons revealed that almost all investigated electrical properties of type L and type H phrenic motoneurons are similar to the analogous properties of type F (fast twitch) and type S (slow twitch) lumbosacral motoneurons, respectively. The apparent exception is the lower mean value of Irh for type L phrenic motoneurons compared with type F lumbosacral motoneurons. 5. For 13 cells, membrane potential was continuously monitored while spontaneous respiratory activity was restored by increasing CO2. It was found that at approximately the same end-tidal CO2 (about 7%) and a similar end-expiratory mean membrane potential level (approximately -70 mV), mean amplitude of peak inspiratory synaptic depolarization was higher in type H motoneurons (8.8 mV, n = 5) than in type L (2.9 mV, n = 8; P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Estimation of the membrane potential of cultured macrophages from the fast potential transient upon microelectrode entry

1983 ◽  
Vol 96 (3) ◽  
pp. 796-801 ◽  
Author(s):  
C Ince ◽  
DL Ypey ◽  
R Van Furth ◽  
AA Verveen
Keyword(s):  
Membrane Potential ◽  
Single Cells ◽  
Membrane Resistance ◽  
Peritoneal Macrophages ◽  
Mean Value ◽  
Membrane Potentials ◽  
Isolated Cells ◽  
Real Value ◽  
Mouse Peritoneal Macrophages ◽  
Peak Value

Analysis of membrane potential recordings upon microelectrode impalement of four types of macrophages (cell lines P388D1 and PU5-1.8, cultured mouse peritoneal macrophages, and cultured human monocytes) reveals that these cells have membrane potentials at least two times more negative than sustained potential values (E(s)) frequently reported. Upon microelectrode entry into the cell (P388D1), the recorded potential drops to a peak value (E(p)) (mean -37 mV for 50 cells, range -15 to -70 mV) within 2 ms, after which it decays to a depolarized potential (E(n)) (mean -12 mV) in about 20 ms. Thereafter, the membrane develops one or a series of slow hyperpolarizations before a final sustained membrane potential (E(s)) (mean -14 mV, range -5 to -40) is established. The mean value of the peak of the first hyperpolarization (E(h)) is -30 mV (range -10 to -55 mV). The initial fast peak transient, measured upon microelectrode entry, was first described and analyzed by Lassen et al. (Lassen, U.V., A.M. T. Nielson, L. Pape, and L. O. Simonsen, 1971, J. Membr. Biol. 6:269-288 for other change in the membrane potential from its real value before impalement to a sustained depolarized value. This was shown to be true for macrophages by two-electrode impalements of single cells. Values of E(p), E(n), E(h), E(s), and membrane resistance (R(m)) measured for the other macrophages were similar to those of P388D1. From these results we conclude that E(p) is a better estimate of the true membrane potential of macrophages than E(s), and that the slow hyperpolarizations upon impalement should be regarded as transient repolarizations back to the original membrane potentials. Thus, analysis of the initial fast impalement transient can be a valuable aid in the estimation of the membrane potential of various sorts of small isolated cells by microelectrodes.

scholarly journals NEW MEMBRANE FORMATION DURING CYTOKINESIS IN NORMAL AND CYTOCHALASIN B-TREATED EGGS OF XENOPUS LAEVIS

1974 ◽  
Vol 60 (3) ◽  
pp. 529-540 ◽  
Author(s):  
Siegfried W. de Laat ◽  
John G. Bluemink
Keyword(s):  
Membrane Potential ◽  
Surface Area ◽  
Cytochalasin B ◽  
Specific Resistance ◽  
Membrane Resistance ◽  
Vitelline Membrane ◽  
High Permeability ◽  
Entire Surface ◽  
Ionic Permeability ◽  
Intracellular Microelectrodes

The electrical membrane potential (Em) and electrical membrane resistance (Rm) were measured continuously during the first cleavage of Xenopus eggs, using intracellular microelectrodes. A sharp hyperpolarization of Em and decrease in Rm can be observed from 6 to 8 min after the onset of cleavage. This moment coincides with the onset of the insertion of new membrane (Bluemink and de Laat, 1973) leading to the formation of the interblastomeric membrane during normal cleavage. Removal of the vitelline membrane or exposure to cytochalasin B (CCB) leads to exposure of the entire surface area of the membrane newly formed during cleavage. These conditions allow for a direct measurement of the permeability properties of the new membrane. It was found that under these conditions Em reaches values about 3 times more negative and Rm reaches values about 1.5–3 times smaller than during normal cleavage. The extent of reduction of Rm can be correlated with the surface area of the newly formed membrane. We conclude that the new membrane has different ionic permeability properties than the pre-existing membrane (most probably a relatively high permeability for K+ ions). Its mean specific resistance is 1–2 kΩ·cm2, as against 74 kΩ·cm2 for the pre-existing membrane. No influence of CCB on the permeability properties of the pre-existing or new membrane could be detected.

Effects of ouabain on background and voltage-dependent currents in canine colonic myocytes

1990 ◽  
Vol 259 (3) ◽  
pp. C402-C408 ◽  
Author(s):  
E. P. Burke ◽  
K. M. Sanders
Keyword(s):  
Membrane Potential ◽  
Potential Gradient ◽  
Circular Muscle ◽  
Input Resistance ◽  
Pump Current ◽  
Muscle Layer ◽  
Membrane Properties ◽  
Resting Potential ◽  
Voltage Dependent ◽  
In Cells

Previous studies have suggested that the membrane potential gradient across the circular muscle layer of the canine proximal colon is due to a gradient in the contribution of the Na(+)-K(+)-ATPase. Cells at the submucosal border generate approximately 35 mV of pump potential, whereas at the myenteric border the pump contributes very little to resting potential. Results from experiments in intact muscles in which the pump is blocked are somewhat difficult to interpret because of possible effects of pump inhibitors on membrane conductances. Therefore, we studied isolated colonic myocytes to test the effects of ouabain on passive membrane properties and voltage-dependent currents. Ouabain (10(-5) M) depolarized cells and decreased input resistance from 0.487 +/- 0.060 to 0.292 +/- 0.040 G omega. The decrease in resistance was attributed to an increase in K+ conductance. Studies were also performed to measure the ouabain-dependent current. At 37 degrees C, in cells dialyzed with 19 mM intracellular Na+ concentration [( Na+]i), ouabain caused an inward current averaging 71.06 +/- 7.49 pA, which was attributed to blockade of pump current. At 24 degrees C or in cells dialyzed with low [Na+]i (11 mM), ouabain caused little change in holding current. With the input resistance of colonic cells, pump current appears capable of generating at least 35 mV. Thus an electrogenic Na+ pump could contribute significantly to membrane potential.

Electrogenic Na+ Transport in a Crustacean Coxal Receptor

1979 ◽  
Vol 78 (1) ◽  
pp. 29-45
Author(s):  
MAURIZIO MIROLLI
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Input Resistance ◽  
Scylla Serrata ◽  
Partial Action ◽  
State Response ◽  
Electrogenic Na Pump ◽  
K Concentration ◽  
Low K ◽  
In Cells

1. The response of the coxal receptors of the crab Scylla serrata to step stretches consisted of a partial action potential, Vα, followed by a steady-state depolarization, V8. The input resistance of the fibre was reduced during V8. 2. In the absence of stimulation, the dendrites of the receptors depolarized when external Na+ was substituted with choline or Li+, and when the external K+ concentration was increased or decreased. The dendrites also depolarized when ouabain was added to the saline. 3. The amplitude of both Vα and V8 was dependent on external Na+. In cells which were depolarized by ouabain, the amplitude of V8 increased when the K+ concentration of the saline was reduced. 4. V8 was followed by a small, but long-lasting, after-potential which was depolarizing when the membrane potential was between −70 and −60 mV. In cells depolarized by ouabain or by low K+ saline, the after-potential became hyperpolarizing. 5. When trains of brief stretches (each 5 ms in duration) were used as stimuli, the cells responded with trains of Vα responses. During this tetanic stimulation the cells hyperpolarized; cessation of the stimulus train was followed by a long-lasting hyperpolarization (PTH). 6. PTH was abolished in Li+ saline, in low K+ saline, and in the presence of ouabain. In control or in low K+ saline, PTH was not accompanied by a decrease in the input resistance of the fibres. 7. It is concluded that an electrogenic Na+ pump (or equivalent process) contributes a substantial fraction of the membrane potential of the unstimulated coxal receptors. Pump activity could be increased by Na+-loading the distal part of the cells with trains of Vα responses. By contrast, during the steady-state response to stretch, the pump was not activated.

The Electrical Properties of a Crustacean Sensory Dendrite

1979 ◽  
Vol 78 (1) ◽  
pp. 1-27
Author(s):  
MAURIZIO MIROLLI
Keyword(s):  
Time Course ◽  
Short Circuit ◽  
Input Resistance ◽  
Scylla Serrata ◽  
Current Pulses ◽  
Length Constant ◽  
Voltage Transient ◽  
Intracellular Microelectrodes ◽  
Voltage Transients ◽  
Sensory Endings

1. The input properties and the response to stretch of a coxal receptor, the S fibre of the crab Scylla serrata, were studied using two and three intracellular microelectrodes. 2. In the relaxed receptor the transmembrane potential ranged from about −60 to −70 mV, and the input resistance, RT, from 1 to 3 MΩ. The input IV relationship, studied by injecting slow-rising current ramps, was not linear either in the hyperpolarizing or in the depolarizing quadrants. 3. Low values of RT and a linear IV relationship were associated with a large leakage of the microelectrodes. 4. The response to step stretches was complex, consisting of an initial depolarizing transient, Vα, and a steady-state depolarizing plateau, V8. Both Vα and V8 propagated with decrement in the fibre which was about 9 mm long. The spatial decrement of Vα and V8 was equal to that of the response to distally injected current pulses of comparable duration and amplitude. 5. On the basis of the spatial decrement of both Vα and V8 the dendrite can be considered equivalent, for current flowing from its distal to its proximal end, to a semi-infinite cable having a length constant of between 4 and 6 cm. 6. The voltage transients recorded in response to long current pulses reached 84% of their final value in a time (t84%) ranging from 150 to 180 ms in fibres in which RT was 2 Mω or larger. t84% was smaller in fibres having a lower RT. 7. The time course of the transients recorded in response to injected current pulses deviated from the semi-infinite cable model in a manner suggesting the presence of a partial short circuit. For this reason the membrane time constant of the fibre is considered larger (by an undetermined amount) than t84%. 8. The fibre presented less resistance to current flowing from its proximal to its distal end than to current flowing in the opposite direction. For this reason, and also because of the time course of the voltage transient, it is concluded that the distal sensory endings of the fibre have the properties of a leaky end termination, even in the non-stimulated receptors.

Structure and electrical properties of eye muscles in cave- and surface-dwelling crayfishes

1980 ◽  
Vol 84 (1) ◽  
pp. 187-199
Author(s):  
D. Mellon ◽  
G. Lnenicka
Keyword(s):  
Input Resistance ◽  
Selective Advantage ◽  
Oculomotor System ◽  
Membrane Resistance ◽  
Muscle Fibres ◽  
Cross Sectional ◽  
Eye Muscles ◽  
Current Voltage ◽  
The Difference ◽  
Cave Dweller

The morphologies and passive electrical parameters of fibres in two eye muscles of a surface- and a cave-dwelling crayfish were compared. In the cave-dwelling form the muscles contained fewer fibres, of less diameter, and hence had a smaller cross-sectional area. Current-voltage relationships were similar in both species. Input resistance was higher in the cave-dweller, but the difference was not as great as would be expected on the basis of geometry alone. Accordingly, the specific membrane resistance of muscle fibres in the cave-dweller is 50–60% smaller than that in the surface-dweller. This may account partially for the observation that identified excitatory junctional potentials in muscles of cave- and surface dwellers have similar amplitudes. We conclude that a functional oculomotor system is maintained in cave-dwelling crayfish, and that this system confers some positive selective advantage.

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