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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Kinetics of inactivation of sodium channels in myelinated nerve from Rana pipiens were studied at 4.5 degrees C using the voltage clamp technique of Dodge & Frankenhaeuser (1958).2. Potassium currents were blocked by cutting the internodes in 20 mM-TEA-Cl + 100 mM-KCl and by adding 12 mM-TEA-Cl to the external Ringer. Leakage and capacitative currents were subtracted electronically.3. Kinetics of recovery from inactivation of the sodium channels were studied by inactivating the channels with a large depolarizing prepulse and allowing the channels to recover at different potentials; the extent of recovery was measured by applying a test pulse at various times after the prepulse.4. Kinetics of development of inactivation were studied by two different methods. The first was to measure the decay of sodium current under a maintained depolarization. The second method was to measure the decay of the peak sodium current in a test pulse as a function of time after the onset of a maintained depolarization. These two methods yielded similar results for the kinetics of inactivation development.5. Contrary to expectations of the Hodgkin-Huxley formalism, the time course of recovery from and development of inactivation is not strictly exponential. Rather, recovery from complete inactivation shows an initial delay which depends on recovery potentials. Development of inactivation at a fixed potential exhibits at least two exponentials.6. The steady-state inactivation curve h(infinity)(E) is asymmetrical and is fitted better by 1/[1+exp (A(1)E+B(1)) +exp (A(2)E+B(2))] than by 1/[1+exp (AE+B)].7. Most of the above kinetic observation on inactivation can be fitted by the following modification of the h system of the Hodgkin-Huxley formalism: [Formula: see text]8. In the analysis it was not necessary to modify the concept of two separate processes, activation and inactivation, governing the opening and closing of the sodium channels.
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PMID:Inactivation of sodium channels: second order kinetics in myelinated nerve. 30 88

1. Sodium currents (INa) and asymmetrical displacement currents (ID) were measured in the same nerve fibres from Rana esculenta under similar conditions. 2. For exploring possible kinetic and steady state relations between INa and ID the following quantities were compared: (i) the activation of the sodium channels and (ii) the charge displacement of ID. 3. The delay of sodium activation increased after hyperpolarization. A corresponding effect on the displacement of charge was not observed. 4. Upon a small depolarization sodium activation rose slower than the displacement of charge, whereas at large depolarizations sodium activation reached a steady level before the charge displacement. 5. Upon repolarization to various levels between -52 and 12 mV relative to the resting potential, the ratio between the time constants of charge displacement and of sodium tail current varied between 3 and 1. 6. In the steady state the sodium activation was one half at about the same potential as the charge displacement but exhibited a clearly steeper voltage dependence. 7. Blocage of sodium channels with tetrodotoxin did not affect the asymmetrical displacement current. Replacing a part of external Na by tris did not alter the sodijm activation process. 8. The results indicate that the asymmetrical displacement of charge may reflect states of the gating mechanism in sodium channels but cannot be considered as a correlate of the Hodgkin Huxley m variable.
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PMID:Asymmetrical displacement current and its relation with the activation of sodium current in the membrane of frog myelinated nerve. 108 37

Pinellia ternata lectin (PTL), a protein exhibiting hemagglutination activity and carbohydrate binding specificity to mannan was purified from rhizome of Pinellia ternata. In this work the actions of PTL on artificial lipid bilayer were investigated by means of the two-compartment system of Mueller and Rudin. The lipid bilayer with resistance more than 10G omega was formed by a solution of lecithin and cholesterol (20 mg/ml and 5 mg/ml respectively) in N-decane. The electrical properties of the lipid bilayer were investigated in voltage clamp mode. Several minutes after the addition of PTL (2 micrograms/ml) in one compartment the channel-like noise as well as a decrease of the resistance of the bilayer were observed. These actions were inhibited by mannan significantly. The resistance increase of the bilayer with PTL-channels could be observed from 2G omega to control level (greater than or equal to 10 G omega) immediately after addition of 40 micrograms/ml mannan. The discrete conduction steps were recorded at low concentration of PTL and at low holding potential. The predominant unit conductance was 35pS in symmetric KCl solution of 100 mmol/L. The selectivity of PTL-channel was estimated from Goldman-Hodgkin-Katz equation by measurement of the reversal potential in an asymmetrical salt solution. The results showed that PTL-channels were cation selective.
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PMID:[Cation channels formed in lipid bilayer by Pinellia ternata lectin]. 137 36

Recordings were made on excised apical membrane patches from vestibular dark cells from the semicircular canal of gerbils to determine if ion channels could be involved in the process of K+ secretion. Both nonselective cation channels [Am. J. Physiol. 262 (Cell Physiol. 31): C1430-C1436, 1992] and K(+)-selective channels were found. The K+ channels occurred in only 0.7% of the patches. In symmetrical 145 mM KCl solutions, the current-voltage (I-V) relation of the K(+)-selective channel was linear, indicating the absence of rectification, and the conductance was 240 +/- 8 pS (n = 8). The Goldman-Hodgkin-Katz equation for current carried solely by K+ could be fitted to the I-V relation in asymmetrical K+ and Na+ solutions and yielded a K+ permeability of 5.78 x 10(-13) cm3/s (n = 12). The channel was shown to be impermeable to Li+, NH4+, N-methyl-D-glucamine, and Cl-. Channel activity increased with depolarization and with increasing free [Ca2+]; for voltages between +40 and -60 mV, the strongest regulation occurred in the range 10(-6) to 10(-5) M Ca2+. Tetraethylammonium (2 x 10(-2) M) had from the cytosolic side no effect on the open probability (Po) but completely inhibited activity from the extracellular side. Po was reduced by Ba2+ (5 x 10(-3) M), verapamil (10(-4) M), quinine (10(-4) M), and quinidine (10(-4) and 10(-3) M), while lidocaine (5 x 10(-3) M) had no measurable effect on Po but decreased the amplitude. Rb+ and Cs+ were either poorly permeable or partially blocked the channel in a voltage-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Maxi K+ channel in apical membrane of vestibular dark cells. 161 10

The present studies examined some of the properties of Cl- channels in renal outer medullary membrane vesicles incorporated into planar lipid bilayers. The predominant channel was anion selective having a PCl/PK ratio of 10 and a unit conductance of 93 pS in symmetric 320 mM KCl. In asymmetric KCl solutions, the I-V relations conformed to the Goldman-Hodgkin-Katz equation. Channel activity was voltage-dependent with a gating charge of unity. This voltage dependence of channel activity may account, at least in part, for the striking voltage dependence of the basolateral membrane Cl- conductance of isolated medullary thick ascending limb segments. The Cl- channels incorporated into the planar bilayers were asymmetrical: the trans surface was sensitive to changes in ionized Ca2+ concentrations and insensitive to reducing KCl concentrations to 10 mM, while the cis side was insensitive to changes in ionized Ca2+ concentrations, but was inactivated by reducing KCl concentrations to 50 mM.
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PMID:Cl- transport in basolateral renal medullary vesicles: II. Cl- channels in planar lipid bilayers. 168 86

A chamber filled with salt solution and separated into two compartments by a Teflon partition with a pore of 700 microns diameter was used to investigate the action of aureofuscin, a polyene antibiotics, on a planar lipid bilayer. The pore was covered with a bilayer formed by a N-decane solution of lecithin and cholesterol (20 mg/ml and 5 mg/ml). The electrical property and ionic permeability of the bilayer were studied by using voltage clamp method. Decrease of the bilayer resistance and the channel-like activity could be observed 20 min after the addition of aureofuscin (10-20 micrograms/ml) to one compartment. The existence of a transmembrane voltage and ionic gradient were not necessary for the channel-forming activity of aureofuscin. Discrete current steps were recorded at a concentration of 1.4 micrograms/ml aureofuscin, with a predominant unit conductance of 4-6 pS in a symmetric KCl, solution of 100 mmol/L. By using Goldmann-Hodgkin-Katz voltage equation the ionic selectivity of the channel formed by aureofuscin was estimated by the reversal potential measured in the asymmetrical solution system. The results showed that aureofuscin channels were more permeable to potassium ion than to chloride ion (PK/PCl approximately 5.2). These data may be used to explain the action of aureofuscin on neurotransmitter release and muscle membrane potential in addition to providing some explanation on its curing effect in clinical use.
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PMID:[Ionic channels formed in the lipid bilayer membranes by aureofuscin, a polyene antibiotics]. 171 13

In a series of 50 cases in which nerve and/or muscle microvasculitis was seen on biopsy, seven were associated with malignancy. In two cases, the cancer was found after the discovery of microvasculitis. All patients exhibited sensory-motor neuropathy, which was often painful and asymmetrical, with a progressive course. ESR and CSF protein levels were always elevated. Motor conduction velocity was slightly reduced in three cases, unmeasurable in one case, and normal in three. Cancers involved were adenocarcinoma in five cases (three prostate and two lung), Hodgkin's disease in one and immunoblastic lymphadenopathy in one. A thorough search for cancer should be performed when microvasculitis is seen in nerve or muscle biopsy specimens, especially when ESR and CSF protein levels are elevated.
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PMID:Nerve and muscle microvasculitis in peripheral neuropathy: a remote effect of cancer? 302 Jan 78

1. Asymmetries in the early time course of the displacement current passing across the membrane after application of equal voltage-clamp pulses in the two directions have been investigated in the squid giant axon. Before making the measurements, Na current was blocked by removal of external Na and treatment with tetrodotoxin. Potassium current was usually blocked by perfusion with CsF, but some experiments were done with intact axons. A signal averaging technique was used to eliminate the symmetrical components of the membrane current.2. The asymmetrical current had a contribution of appreciable size attributed to the movement of mobile charges or dipoles in the membrane. This was manifested as an outward current rising rapidly to a peak on depolarization of the membrane and then declining exponentially to zero, followed at the end of the pulse by an inward surge of current with a similar time course. There was also a sustained flow of current outwards during the pulse, arising from ionic leakage with a rectifying characteristic.3. The identification of the exponentially changing current component with the displacement of charged particles forming an integral part of the membrane was supported by the demonstration that the total transfer of charge was equal and opposite at the beginning and end of the pulse, that it reached saturation when the internal potential was taken to a sufficient positive value, and that its size was unaffected by temperature, although its time constant had a large temperature coefficient.4. The disposition of the mobile charges in the steady state was shown to obey a Boltzmann distribution. At the midpoint of the distribution curve, the proportion of the charge displaced underwent an e-fold change for a 19 mV change in potential. The effective valency of the particles, that is their actual charge multiplied by the fraction of the electric field acting on them, was therefore 1.3.5. The total quantity of mobile charge was estimated as about 1500 x 10(-12) C for 0.05 cm(2) of membrane, corresponding to some 1900 charges/mum(2).6. The identification of these mobile charges with the gating particles responsible for controlling Na conductance was supported by the findings that (a) their time constants were the same as those of Hodgkin & Huxley's ;m' system, both in absolute magnitude and in their dependence on potential and temperature, (b) the transition potential at which the charges were evenly distributed on the two sides of the membrane also agreed with that for the ;m' system in intact axons, and its value was similarly shifted in a positive direction by a reduction in internal ionic strength or by raising the external Ca concentration, (c) comparison of the steepness of the curves governing on the one hand the steady-state distribution of the mobile charges and on the other the Na conductance, suggested that an effective cooperation of the charges in groups of three was involved, again in excellent agreement with the ;m' system.7. Displacement of the mobile charges was unaffected by external pH over the range 5-8, but preliminary observations showed that 1% procaine reduced the total charge transfer to somewhat less than 40% of the initial value, and roughly halved the time constant.
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PMID:Kinetics and steady-state properties of the charged system controlling sodium conductance in the squid giant axon. 441 38

This paper describes dissipative Cl(-) transport in "porous" lipid bilayer membranes, i.e., cholesterol-containing membranes exposed to 1-3 x 10(-7) M amphotericin B. P(DCl) (cm.s(-1)), the diffusional permeability coefficient for Cl(-), estimated from unidirectional (36)Cl(-) fluxes at zero volume flow, varied linearly with the membrane conductance (Gm, ohm(-1).cm(-2)) when the contributions of unstirred layers to the resistance to tracer diffusion were relatively small with respect to the membranes; in 0.05 M NaCl, P(DCl) was 1.36 x 10(-4) cm.s(-1) when Gm was 0.02 ohm(-1).cm(-2). Net chloride fluxes were measured either in the presence of imposed concentration gradients or electrical potential differences. Under both sets of conditions: the values of P(DCl) computed from zero volume flow experiments described net chloride fluxes; the net chloride fluxes accounted for approximately 90-95% of the membrane current density; and, the chloride flux ratio conformed to the Ussing independence relationship. Thus, it is likely that Cl(-) traversed aqueous pores in these anion-permselective membranes via a simple diffusion process. The zero current membrane potentials measured when the aqueous phases contained asymmetrical NaCl solutions could be expressed in terms of the Goldman-Hodgkin-Katz constant field equation, assuming that the P(DNa)/P(DCl) ratio was 0.05. In symmetrical salt solutions, the current-voltage properties of these membranes were linear; in asymmetrical NaCl solutions, the membranes exhibited electrical rectification consistent with constant-field theory. It seems likely that the space charge density in these porous membranes is sufficiently low that the potential gradient within the membranes is approximately linear; and, that the pores are not electrically neutral, presumably because the Debye length within the membrane phase approximates the membrane thickness.
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PMID:Chloride transport in porous lipid bilayer membranes. 470 8

The voltage and time dependence of outward-rectifying K+ currents (IK,out) measured in protoplasts from tobacco cell suspension cultures in the whole-cell configuration of the patch-clamp technique are quantitatively analyzed. The voltage and time dependence was described according to the Hodgkin and Huxley model for IK,out currents in the squid giant axon, and to allow comparison, in analogy with the quantitative analysis of IK,out currents in Vicia faba guard cell protoplasts as described by Schroeder (J. Membrane Biol., 107:229-235, 1989). The IK,out from tobacco could be described by a similar model as the IK,out from guard cell protoplasts (i.e., sigmoid activation time course, activation variable raised to second power, single exponential deactivating tail currents, absence of inactivation). However, in contrast to guard cells, both the activation and deactivation time constants were strongly voltage dependent in tobacco protoplasts. The voltage dependence of the transition rates for channel opening and channel closing was slightly asymmetrical and inverse to the asymmetry found in guard cells. The data presented show that the voltage-dependent kinetic properties of the IK,out conductance of tobacco protoplasts are different from these properties in guard cell protoplasts. This analysis provides a basis for the study of IK,out conductance function and modulation.
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PMID:Hodgkin-Huxley analysis of whole-cell outward rectifying K(+)-currents in protoplasts from tobacco cell suspension cultures. 768 83


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