scholarly journals Membrane capacitance in frog cut twitch fibers mounted in a double vaseline-gap chamber.

1990 ◽  
Vol 96 (2) ◽  
pp. 225-256 ◽  
Author(s):  
W K Chandler ◽  
C S Hui
Keyword(s):  
Plasma Membranes ◽  
Unit Length ◽  
Electrical Measurements ◽  
Tetraethylammonium Chloride ◽  
Internal Solution ◽  
Current Passing ◽  
Longitudinal Resistance ◽  
Small Change ◽  
Internal Longitudinal Resistance ◽  
Earth Potential

In experiments on cut muscle fibers mounted in a double Vaseline-gap chamber, electrical measurements are usually made by measuring the voltage V1(t) in one end pool and by passing current I2(t) from the other end pool to the central pool, which is usually clamped to earth potential. The voltage in the current-passing end pool is denoted by V2(t). This article describes how the value of the holding current, Ih, and the values of delta V2(infinity)/delta V1(infinity) and delta I2(infinity)/delta V1(infinity) that are associated with a small change in V1(t) can be used to estimate the linear cable parameters rm, ri, and re in a cut fiber that has been equilibrated with a Cs-containing internal solution. rm, ri, and re represent, respectively, the resistance of the plasma membranes, the internal longitudinal resistance, and the external longitudinal resistance under the Vaseline seals, all for a unit length of fiber. The apparent capacitance, Capp, of the preparation is defined to equal integral of infinity 0 delta I2,tr(t) dt/delta V1(infinity), in which delta I2,tr(t) represents the transient component of current that is associated with a change in V1(t) of amplitude delta V1(infinity). A method is described to estimate cm, the capacitance of the plasma membranes per unit length of fiber, from Capp and the values of rm, ri, and re. In experiments carried out with a tetraethylammonium chloride (TEA.Cl) solution at 13-14 degrees C in the central pool, cm remained stable for as long as 3-4 h. The values of cm, 0.19 microF/cm on average, and their variation with fiber diameter are similar to published results from intact fibers. This article also describes the different pathways that are taken by the current that flows from the current-passing end pool to the central pool. Approximately two-thirds of delta I2,tr(t) flows across the capacitance of the plasma membranes in the central-pool region. The rest flows either across plasma membranes that are under the two Vaseline seals or directly from the current-passing end pool to the central pool, across the external longitudinal resistance under the Vaseline seal. [There is also a current that flows directly from the voltage-measuring end pool to the central pool but this does not contribute to delta I2,tr(t).]

scholarly journals Intramembranous charge movement in frog cut twitch fibers mounted in a double vaseline-gap chamber.

1990 ◽  
Vol 96 (2) ◽  
pp. 257-297 ◽  
Author(s):  
C S Hui ◽  
W K Chandler
Keyword(s):  
Voltage Dependence ◽  
Unit Length ◽  
Boltzmann Distribution ◽  
Distribution Functions ◽  
Charge Movement ◽  
Tetraethylammonium Chloride ◽  
Maximum Charge ◽  
Boltzmann Function ◽  
State Charge ◽  
Current Record

Intramembranous charge movement was measured in cut twitch fibers mounted in a double Vaseline-gap chamber with either a tetraethylammonium chloride (TEA.Cl) or a TEA2.SO4 solution (13-14 degrees C) in the central pool. Charge vs. voltage data were fitted by a single two-state Boltzmann distribution function. The average values of V (the voltage at which steady-state charge is equally distributed between the two Boltzmann states), k (the voltage dependence factor), and qmax/cm (the maximum charge divided by the linear capacitance, both per unit length of fiber) were V = -53.3 mV (SEM, 1.1 mV), k = 6.3 mV (SEM, 0.3 mV), qmax/cm = 18.0 nC/microF (SEM, 1.1 nC/microF) in the TEA.Cl solution; and V = -35.1 mV (SEM, 1.8 mV), k = 10.5 mV (SEM, 0.9 mV), qmax/cm = 36.3 nC/microF (SEM, 3.2 nC/microF) in the TEA2.SO4 solution. These values of k are smaller than those previously reported for cut twitch fibers and are as small as those reported for intact fibers. If a correction is made for the contributions of currents from under the Vaseline seals, V = -51.2 mV (SEM, 1.1 mV), k = 7.2 mV (SEM, 0.4 mV), qmax/cm = 22.9 nC/microF (SEM, 1.4 nC/microF) in the TEA.Cl solution; and V = -34.0 mV (SEM, 1.9 mV), k = 10.1 mV (SEM, 1.1 mV), qmax/cm = 38.8 nC/microF (SEM, 3.2 nC/microF) in the TEA2.SO4 solution. With this correction, however, the fit of the theoretical curve to the data is poor. A good fit with this correction can be obtained with a sum of two Boltzmann distribution functions. The first has average values V = -33.0 mV (SEM, 2.8 mV), k = 11.0 mV (SEM, 0.5 mV), qmax/cm = 10.6 nC/microF (SEM, 1.0 nC/microF) in the TEA.Cl solution; and V = -20.0 mV (SEM, 3.3 mV), k = 17.0 mV (SEM, 2.0 mV), qmax/cm = 36.4 nC/microF (SEM, 2.3 nC/microF) in the TEA2.SO4 solution. The second has average values V = -56.5 mV (SEM, 1.3 mV), k = 2.9 mV (SEM, 0.4 mV), qmax/cm = 13.2 nC/microF (SEM, 1.0 nC/microF) in the TEA.Cl solution; and V = -41.6 mV (SEM, 1.4 mV), k = 2.5 mV (SEM, 0.8 mV), qmax/cm = 11.8 nC/microF (SEM, 1.7 nC/microF) in the TEA2.SO4 solution. When a fiber is depolarized to near V of the second Boltzmann function, a slowly developing "hump" appears in the ON-segment of the current record.(ABSTRACT TRUNCATED AT 400 WORDS)

Decrease in rat taste receptor cell intracellular pH is the proximate stimulus in sour taste transduction

2001 ◽  
Vol 281 (3) ◽  
pp. C1005-C1013 ◽  
Author(s):  
Vijay Lyall ◽  
Rammy I. Alam ◽  
Duy Q. Phan ◽  
Glenn L. Ereso ◽  
Tam-Hao T. Phan ◽  
...  
Keyword(s):  
Intracellular Ph ◽  
Plasma Membranes ◽  
Taste Receptor ◽  
Taste Perception ◽  
Sour Taste ◽  
Taste Transduction ◽  
Taste Reception ◽  
Small Change ◽  
Strong Acids ◽  
Paracellular Shunt

Taste receptor cells (TRCs) respond to acid stimulation, initiating perception of sour taste. Paradoxically, the pH of weak acidic stimuli correlates poorly with the perception of their sourness. A fundamental issue surrounding sour taste reception is the identity of the sour stimulus. We tested the hypothesis that acids induce sour taste perception by penetrating plasma membranes as H+ ions or as undissociated molecules and decreasing the intracellular pH (pHi) of TRCs. Our data suggest that taste nerve responses to weak acids (acetic acid and CO2) are independent of stimulus pH but strongly correlate with the intracellular acidification of polarized TRCs. Taste nerve responses to CO2 were voltage sensitive and were blocked with MK-417, a specific blocker of carbonic anhydrase. Strong acids (HCl) decrease pHi in a subset of TRCs that contain a pathway for H+ entry. Both the apical membrane and the paracellular shunt pathway restrict H+ entry such that a large decrease in apical pH is translated into a relatively small change in TRC pHi within the physiological range. We conclude that a decrease in TRC pHi is the proximate stimulus in rat sour taste transduction.

Effects of manganese chloride, verapamil, and hypoxia on the rate-dependent increase in internal longitudinal resistance of rabbit myocardium

1989 ◽  
Vol 67 (4) ◽  
pp. 263-268 ◽  
Author(s):  
Julio Alvarez ◽  
Georgina Rousseau ◽  
Francisco Dorticós ◽  
Jesús Morlans
Keyword(s):  
Conduction Velocity ◽  
Slow Inward Current ◽  
Channel Blockers ◽  
Rate Dependent ◽  
Rabbit Myocardium ◽  
Intracellular Ca ◽  
Longitudinal Resistance ◽  
Main Determinants ◽  
Induced Changes ◽  
Internal Longitudinal Resistance

The effects of high rates of stimulation on the internal longitudinal restivity (Ri) and conduction velocity (θ) were studied on rabbit papillary muscle preparations using a silicon-oil chamber. Increasing the rate from 75 to 150/min caused Ri to rise and θ to decrease. The maximum rate of depolarization and action potential duration were also decreased. At a rate of 300/min the effects were more pronounced. Blockade of the slow inward current (Isi) and of the Na–Ca exchange by MnCl2 (5 mmol/L) did not prevent rate-induced changes in these variables. Verapamil (0.02 mmol/L) was also ineffective. Hypoxia [Formula: see text] at 75/min induced changes in Ri and θ which were similar to those recorded at 150/min under aerobic conditions. The effects of high rates of stimulation were potentiated under hypoxia. From the present results it is suggested that Isi and the Na–Ca exchange are not the main determinants of the rate-induced increase in Ri, which could be determined by other intracellular Ca-release mechanisms or by a decrease in myoplasmic pH.Key words: intercellular coupling, conduction velocity, calcium channel blockers.

A method for measurement of internal longitudinal resistance in papillary muscle

1986 ◽  
Vol 251 (1) ◽  
pp. H210-H217 ◽  
Author(s):  
J. W. Buchanan ◽  
S. Oshita ◽  
T. Fujino ◽  
L. S. Gettes
Keyword(s):  
Constant Flow ◽  
Flow Rates ◽  
Ionic Content ◽  
Extracellular Compartment ◽  
Theoretical Assumptions ◽  
Potential Recording ◽  
Longitudinal Resistance ◽  
Extracellular Resistance ◽  
Internal Longitudinal Resistance

We have modified the original Weidmann method for the measurement of internal longitudinal resistance in ventricular muscle by using air rather than silicon oil to insulate guinea pig papillary muscles and by omitting the tetrodotoxin inactivation of a portion of the preparation and have examined the requirements necessary for the theoretical assumptions to be satisfied by this or similar preparations. We found a homogeneous depolarization wavefront beyond about 1 mm from the stimulating electrodes. The adequacy of the interelectrode spacing was identified by a discrete plateau in the extracellular potential recording. The extracellular resistance in this preparation was sensitive to changes in the volume of the extracellular compartment, which we manipulated by changing inflow and outflow rates, and to changes in total ionic content of the superfusate. Our results establish the essential nature of maintaining constant flow rates and total ionic content and suggest that changes in volume and ionic content of a restricted extracellular space could conceivably influence conduction in vivo.

Electrophysiological characterization of ATPases in native synaptic vesicles and synaptic plasma membranes

2010 ◽  
Vol 427 (1) ◽  
pp. 151-159 ◽  
Author(s):  
Petr Obrdlik ◽  
Kerstin Diekert ◽  
Natalie Watzke ◽  
Christine Keipert ◽  
Ulrich Pehl ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Atpase Activity ◽  
Synaptic Vesicles ◽  
Sucrose Gradient ◽  
Plasma Membranes ◽  
Specific Inhibitor ◽  
Chloride Conductance ◽  
Atpase Inhibitor ◽  
Electrical Measurements ◽  
Supported Membrane

Vesicular V-ATPase (V-type H+-ATPase) and the plasma membrane-bound Na+/K+-ATPase are essential for the cycling of neurotransmitters at the synapse, but direct functional studies on their action in native surroundings are limited due to the poor accessibility via standard electrophysiological equipment. We performed SSM (solid supported membrane)-based electrophysiological analyses of synaptic vesicles and plasma membranes prepared from rat brains by sucrose-gradient fractionation. Acidification experiments revealed V-ATPase activity in fractions containing the vesicles but not in the plasma membrane fractions. For the SSM-based electrical measurements, the ATPases were activated by ATP concentration jumps. In vesicles, ATP-induced currents were inhibited by the V-ATPase-specific inhibitor BafA1 (bafilomycin A1) and by DIDS (4,4′-di-isothiocyanostilbene-2,2′-disulfonate). In plasma membranes, the currents were inhibited by the Na+/K+-ATPase inhibitor digitoxigenin. The distribution of the V-ATPase- and Na+/K+-ATPase-specific currents correlated with the distribution of vesicles and plasma membranes in the sucrose gradient. V-ATPase-specific currents depended on ATP with a K0.5 of 51±7 μM and were inhibited by ADP in a negatively co-operative manner with an IC50 of 1.2±0.6 μM. Activation of V-ATPase had stimulating effects on the chloride conductance in the vesicles. Low micromolar concentrations of DIDS fully inhibited the V-ATPase activity, whereas the chloride conductance was only partially affected. In contrast, NPPB [5-nitro-2-(3-phenylpropylamino)-benzoic acid] inhibited the chloride conductance but not the V-ATPase. The results presented describe electrical characteristics of synaptic V-ATPase and Na+/K+-ATPase in their native surroundings, and demonstrate the feasibility of the method for electrophysiological studies of transport proteins in native intracellular compartments and plasma membranes.

Metallurgical Effects of Grain Boundary Ledges

1977 ◽  
Vol 35 ◽  
pp. 126-129
Author(s):  
L.E. Murr
Keyword(s):  
Grain Boundary ◽  
Quantitative Data ◽  
Mechanical Treatment ◽  
Unit Length ◽  
Physical And Mechanical Properties ◽  
Direct Observations ◽  
Transmission Electron ◽  
Properties Of Materials ◽  
Thermo Mechanical Treatment ◽  
Ledge Density

Ledges in grain boundaries can be identified by their characteristic contrast features (straight, black-white lines) distinct from those of lattice dislocations, for example1,2 [see Fig. 1(a) and (b)]. Simple contrast rules as pointed out by Murr and Venkatesh2, can be established so that ledges may be recognized with come confidence, and the number of ledges per unit length of grain boundary (referred to as the ledge density, m) measured by direct observations in the transmission electron microscope. Such measurements can then give rise to quantitative data which can be used to provide evidence for the influence of ledges on the physical and mechanical properties of materials.It has been shown that ledge density can be systematically altered in some metals by thermo-mechanical treatment3,4.

Characterization of microtubules by dark-field STEM and replication

1991 ◽  
Vol 49 ◽  
pp. 152-153
Author(s):  
S.B. Andrews ◽  
R.D. Leapman ◽  
P.E. Gallant ◽  
T.S. Reese
Keyword(s):  
Protein Interactions ◽  
Low Dose ◽  
Unit Length ◽  
Dark Field ◽  
Carbon Films ◽  
Microtubule Associated Proteins ◽  
Molecular Weights ◽  
Freeze Dried ◽  
Protein Motors ◽  
Associated Proteins

As part of a study on protein interactions involved in microtubule (MT)-based transport, we used the VG HB501 field-emission STEM to obtain low-dose dark-field mass maps of isolated, taxol-stabilized MTs and correlated these micrographs with detailed stereo images from replicas of the same MTs. This approach promises to be useful for determining how protein motors interact with MTs. MTs prepared from bovine and squid brain tubulin were purified and free from microtubule-associated proteins (MAPs). These MTs (0.1-1 mg/ml tubulin) were adsorbed to 3-nm evaporated carbon films supported over Formvar nets on 600-m copper grids. Following adsorption, the grids were washed twice in buffer and then in either distilled water or in isotonic or hypotonic ammonium acetate, blotted, and plunge-frozen in ethane/propane cryogen (ca. -185 C). After cryotransfer into the STEM, specimens were freeze-dried and recooled to ca.-160 C for low-dose (<3000 e/nm2) dark-field mapping. The molecular weights per unit length of MT were determined relative to tobacco mosaic virus standards from elastic scattering intensities. Parallel grids were freeze-dried and rotary shadowed with Pt/C at 14°.

On the structural organization of biological pumps and channels

1984 ◽  
Vol 42 ◽  
pp. 138-141
Author(s):  
G. Zampighi ◽  
M. Kreman
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Plasma Membranes ◽  
Transport Proteins ◽  
Molecular Organization ◽  
Passive Transport ◽  
Concentration Gradients ◽  
Cell Functions ◽  
Natural Concentration ◽  
Active Transport System

The plasma membranes of most animal cells contain transport proteins which function to provide passageways for the transported species across essentially impermeable lipid bilayers. The channel is a passive transport system which allows the movement of ions and low molecular weight molecules along their concentration gradients. The pump is an active transport system and can translocate cations against their natural concentration gradients. The actions and interplay of these two kinds of transport proteins control crucial cell functions such as active transport, excitability and cell communication. In this paper, we will describe and compare several features of the molecular organization of pumps and channels. As an example of an active transport system, we will discuss the structure of the sodium and potassium ion-activated triphosphatase [(Na+ +K+)-ATPase] and as an example of a passive transport system, the communicating channel of gap junctions and lens junctions.

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