scholarly journals Application of silk fibroin to functional membranes: Relationship between conditions of membrane preparation, membrane potential and ion permeability.

1988 ◽  
Vol 44 (4) ◽  
pp. 193-198 ◽  
Author(s):  
Aio Kitamura ◽  
Akio Shibamoto ◽  
Makoto Demura
Keyword(s):  
Membrane Potential ◽  
Silk Fibroin ◽  
Membrane Preparation ◽  
Ion Permeability ◽  
Functional Membranes

Effect of pinacidil on ion permeability in resting and contracted resistance vessels

1990 ◽  
Vol 259 (1) ◽  
pp. H14-H22 ◽  
Author(s):  
L. M. Videbaek ◽  
C. Aalkjaer ◽  
A. D. Hughes ◽  
M. J. Mulvany
Keyword(s):  
Membrane Potential ◽  
Mechanism Of Action ◽  
Ion Permeability ◽  
K Channels ◽  
Complete Relaxation ◽  
Resistance Vessels ◽  
Flux Measurements ◽  
22Na Uptake ◽  
K Permeability ◽  
Cl Permeability

Pinacidil is thought to cause vasodilatation by opening K+ channels and consequent hyperpolarization. This proposed mechanism of action is based mainly on membrane potential measurements and 42K or 86Rb efflux experiments under resting conditions. We have measured the simultaneous effect of pinacidil on force and membrane potential in resting and norepinephrine-contracted rat mesenteric resistance vessels. Also the effect of pinacidil on 42K and 36Cl efflux and 22Na uptake in the absence and presence of norepinephrine was examined. From the membrane potential and ion flux measurements the ion permeabilities were calculated. In both resting and norepinephrine-contracted vessels, pinacidil caused a large hyperpolarization, the latter situation being associated with an almost complete relaxation. In both resting and norepinephrine-stimulated vessels, pinacidil caused a large increase in K+ permeability and a decrease in Cl-permeability, whereas no significant change of Na+ permeability was found. Our results suggest that pinacidil causes vasodilation due to hyperpolarization. The major cause for the hyperpolarization is an increase in K+ permeability.

scholarly journals RECTIFICATION AND INDUCTANCE IN THE SQUID GIANT AXON

1941 ◽  
Vol 25 (1) ◽  
pp. 29-51 ◽  
Author(s):  
Kenneth S. Cole
Keyword(s):  
Membrane Potential ◽  
Electrical Properties ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Constant Current ◽  
Ion Permeability ◽  
Squid Axon ◽  
Axon Membrane ◽  
Piezoelectric Structure ◽  
In Series

Previous measurements have shown that the electrical properties of the squid axon membrane are approximately equivalent to those of a circuit containing a capacity shunted by an inductance and a rectifier in series. Selective ion permeability of a membrane separating two electrolytes may be expected to give rise to the rectification. A quasi-crystalline piezoelectric structure of the membrane is a plausible explanation of the inductance. Some approximate calculations of behavior of an axon with these membrane characteristics have been made. Fair agreement is obtained with the observed constant current subthreshold potential and impedance during the foot of the action potential. In a simple case a formal analogy is found between the calculated membrane potential and the excitability defined by the two factor formulations of excitation. Several excitation phenomena may then be explained semi-quantitatively by further assuming the excitability proportional to the membrane potential. Some previous measurements and subthreshold potential and excitability observations are not consistent with the circuit considered and indicate that this circuit is only approximately equivalent to the membrane.

A new method for determination of relative ion permeabilities in isolated cells

1985 ◽  
Vol 248 (5) ◽  
pp. C399-C405 ◽  
Author(s):  
G. A. Kimmich ◽  
J. Randles ◽  
D. Restrepo ◽  
M. Montrose
Keyword(s):  
Membrane Potential ◽  
Epithelial Cells ◽  
Intestinal Epithelial Cells ◽  
Membrane Vesicle ◽  
Ionic Composition ◽  
Intestinal Epithelial ◽  
Ion Permeability ◽  
Relative Permeabilities ◽  
Isolated Cells

The unidirectional influx of the lipophilic cation tetraphenylphosphonium (TPP+) into isolated epithelial cells is a function of the membrane potential that exists across the cellular plasma membrane. Because of the potential dependence, [14C]TPP+ influx can be used as a qualitative sensor of changes in the membrane potential induced by diffusion of ions after the experimental imposition of transmembrane ion gradients. This report describes a "crossover" procedure in which the influx of [14C]TPP+ during systematic changes in the ionic composition of incubation media is used to identify conditions in which no change in membrane potential occurs. The ion ratio at the crossover provides a measure of the relative permeabilities of the two test ions being compared. By using this approach, the ion permeabilities for intestinal epithelial cells prepared from White Rock chickens can be ranked relative to the permeability of Na+ (PNa), i.e., when PNa is equal to 1.0. The permeability sequence and relative values for ion permeability in this system are tris(hydroxymethyl)aminomethane-gluconate (less than 0.1) less than Li+ (0.3) less than Na+ (1.0) less than Cl- (2.0) less than K+ (6.0) = NO3- (6.0) less than SCN- (18) less than K+ + valinomycin (40). The procedure is general enough in principle to be of broad application to a wide variety of cell or membrane vesicle preparations.

Unusual potassium channels mediate nonadrenergic noncholinergic nerve-mediated inhibition in opossum esophagus

1985 ◽  
Vol 63 (2) ◽  
pp. 107-112 ◽  
Author(s):  
J. Jury ◽  
L. P. Jager ◽  
E. E. Daniel
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Cell Membrane ◽  
Guinea Pig ◽  
Smooth Muscle Cell ◽  
Muscle Cell ◽  
Membrane Resistance ◽  
Potassium Ion ◽  
Ion Permeability ◽  
Muscle Cell Membrane

Field stimulation of the circular muscle of the opossum esophagus produces a transient hyperpolarization (inhibitory junction potential, IJP) followed by an "off" depolarization. A similar nonadrenergic, noncholinergic (NANC) response in guinea pig taenia caecum has been shown to be due to an increase in the potassium ion permeability of the smooth muscle cell membrane. Double sucrose gap studies showed a decrease in resistance during the IJP, and a reversal at an estimated membrane potential of about −90 mV (4 mM K+). The reversal potential was dependent on the extracellular potassium concentration, shifting to −75 mV when the potassium in the superfusion medium was increased to 10 mM. The IJP in the opossum esophageal circular smooth muscle is therefore like the IJP of the guinea pig taenia caecum in that it is probably due to a selective increase in potassium ion permeability. Potassium conductance blocking agents, tetraethylammonium chloride (TEA, 20 mM) and 4-aminopyridine (4-AP, 5 mM) both caused a depolarization of the smooth muscle cell membrane, but TEA increased the membrane resistance, whereas 4-AP did not affect the membrane conductance in a consistent way. A decrease in IJP amplitude owing to these agents was not apparent. Apamin (10 μM) did not affect the membrane potential, the membrane resistance, or the IJP. Quinine (0.1 mM) produced effects quantitatively similar to those of TEA. Quinine (1 mM) did abolish the IJP, however, this was likely due to a blockade of impulse transmission of the intramural nerves. These results suggest that the receptor-operated channels opened by the NANC-nerve mediator in this tissue are unusual in that they are different from those functioning to maintain the resting membrane potential and they differ from those involved in the IJP in the guinea pig taenia caecum.

scholarly journals MEMBRANE POTENTIAL OF THE SQUID GIANT AXON DURING CURRENT FLOW

1941 ◽  
Vol 24 (4) ◽  
pp. 551-563 ◽  
Author(s):  
Kenneth S. Cole ◽  
Howard J. Curtis
Keyword(s):  
Membrane Potential ◽  
Membrane Conductance ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Squid Giant Axon ◽  
Ion Permeability ◽  
Absolute Value ◽  
Initial Transient ◽  
Constant Change ◽  
Fine Capillary

The squid giant axon was placed in a shallow narrow trough and current was sent in at two electrodes in opposite sides of the trough and out at a third electrode several centimeters away. The potential difference across the membrane was measured between an inside fine capillary electrode with its tip in the axoplasm between the pair of polarizing electrodes, and an outside capillary electrode with its tip flush with the surface of one polarizing electrode. The initial transient was roughly exponential at the anode make and damped oscillatory at the sub-threshold cathode make with the action potential arising from the first maximum when threshold was reached. The constant change of membrane potential, after the initial transient, was measured as a function of the total polarizing current and from these data the membrane potential is obtained as a function of the membrane current density. The absolute value of the resting membrane resistance approached at low polarizing currents is about 23 ohm cm.2. This low value is considered to be a result of the puncture of the axon. The membrane was found to be an excellent rectifier with a ratio of about one hundred between the high resistance at the anode and the low resistance at the cathode for the current range investigated. On the assumption that the membrane conductance is a measure of its ion permeability, these experiments show an increase of ion permeability under a cathode and a decrease under an anode.

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