Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0019829 (Hodgkin's disease)
 30,247 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Currents were generated by depolarizing pulses in voltage-clamped, dissociated neurons from the CA1 region of adult guinea pig hippocampus in solutions containing 1 microm tetrodotoxin. When the extracellular potassium concentration was 100 mM, the currents reversed at -8.1 +/- 1.6 mV (n = 5), close to the calculated potassium equilibrium potential of -7 mV. The currents were depressed by 30 mM tetraethylammonium in the extracellular solution but were unaffected by 4-aminopyridine at concentrations of 0.5 or 1 mM. It was concluded that the currents were depolarization-activated potassium currents. Instantaneous current-voltage curves were nonlinear but could be fitted by a Goldman-Hodgkin-Katz equation with PNa/PK = 0.04. Conductance-voltage curves could be described by a Boltzmann-type equation: the average maximum conductance was 65.2 +/- 15.7 nS (n = 9) and the potential at which gK was half-maximal was -4.8 +/- 3.9 mV (mean +/- 1 SEM, n = 10). The relationship between the null potential and the extracellular potassium concentration was nonlinear and could be fitted by a Goldman-Hodgkin-Katz equation with PNa/PK = 0.04. The rising phase of potassium currents and the decay of tail currents could be fitted with exponentials with single time constants that varied with membrane potential. Potassium currents inactivated to a steady level with a time constant of approximately 450 ms that did not vary with potential. The currents were depressed by substituting cobalt or cadmium for extracellular calcium but similar effects were not obtained by substituting magnesium for calcium.
J Gen Physiol 1988 Aug
PMID:Potassium current activated by depolarization of dissociated neurons from adult guinea pig hippocampus. 284 59

We tried to reproduce some basic implications of the Hodgkin-Huxley-Frankenhaeuser formalism by measuring sodium currents in single myelinated nerve fibres with a commercially available version of the potential clamp device according to Nonner. The following contradictory observations were made: 1. The potential dependence of the time to peak sodium currents showed a discontinuity around the sodium equilibrium potential. 2. Defining the sodium permeability PNa by the constant field equation and fitting the peak PNa-voltage relation by a sigmoid function we obtained unbelievable high values of PNa at rest. 3. Testing PNa as calculated by the constant field equation by so-called "sodium tail current" experiments we obtained instantaneous changes of PNa. Summing up, neither the kinetics of sodium currents nor the constant field concept as tested with the equipment used seem to agree satisfactorily with the standard data of sodium currents in Ranvier nodes.
Gen Physiol Biophys 1988 Dec
PMID:Inconsistent sodium current records derived on Ranvier nodes with a commercially available potential clamp device according to Nonner. 285 83

We have examined the Ca2+ content and pathways of Ca2+ transport in frog rod outer segments using the Ca2+-indicating dye arsenazo III. The experiments employed suspensions of outer segments of truncated, but physiologically functional, frog rods (OS-IS), intact isolated outer segments (intact OS), and leaky outer segments (leaky OS with a plasma membrane leaky to small solutes, but with sealed disk membranes). We observed the following. Intact OS or OS-IS isolated and purified in Percoll-Ringer's solution contained an average of 2.2 mM total Ca2+, while leaky OS contained 2.0 mM total Ca2+. This suggests that most of the Ca2+ in OS-IS is contained inside OS disks. Phosphodiesterase inhibitors increased the Ca2+ content to approximately 4.2 mM in intact OS or OS-IS, whereas the Ca2+ content of leaky OS was not altered. Na-Ca exchange was the dominant pathway for Ca2+ efflux in both intact and leaky OS/OS-IS. The rate of Na-Ca exchange in intact OS/OS-IS was half-maximal between 30 and 50 mM Na+; at 50 mM Na+, this amounted to 5.8 X 10(7) Ca2+/OS X s or 0.05 mM total Ca2+/s. This is much larger than the Ca2+ component of the dark current. Other alkali cations could not replace Na+ in Na-Ca exchange in either OS-IS or leaky OS. They inhibited the rate of Na-Ca exchange (K greater than or equal to Rb greater than Cs greater than or equal to Li greater than TMA) and, as the inhibition became greater, a delay developed in the onset of Na-Ca exchange. The inhibition of Na-Ca exchange by alkali cations correlates with the prolonged duration of the photoresponse induced by these cations (Hodgkin, A. L., P. A. McNaughton, and B. J. Nunn. 1985. Journal of Physiology. 358:447-468). In addition to Na-Ca exchange, disk membranes in leaky OS showed a second pathway of Ca2+ transport activated by cyclic GMP (cGMP). The cGMP-activated pathway required the presence of alkali cations and had a maximal rate of 9.7 X 10(6) Ca2+/OS X s. cGMP caused the release of only 30% of the total Ca2+ from leaky OS. The rate of Na-Ca exchange in leaky OS amounted to 1.9 X 10(7) Ca2+/OS X s.(ABSTRACT TRUNCATED AT 400 WORDS)
J Gen Physiol 1987 Mar
PMID:Na+- and cGMP-induced Ca2+ fluxes in frog rod photoreceptors. 303 Nov 99

The Hodgkin-Huxley (1952) model was used to calculate intracellular potentials by the method of Joyner et al. (1978). Extracellular potentials were estimated on the basis of a mathematical model proposed by us. It has shown that, irrespective of practical isopotentiality of the membrane of a local inhomogeneity, the latter affects extracellular potentials in two ways: 1) through changes in the potential profile in the region of the structure before the inhomogeneity; 2) through its own potential profile. The first effect is considerably greater than the second one, but the second is greater than the effect of the equal portion of the thin fibre. Increase in the diameter or length of an inhomogeneity is combined with such changes in the potential profile, that the effect of the inhomogeneity on the extracellular potential amplitude is practically independent of its actual size. The extracellular potential waveform substantially depends on the ratio of the diameters of the two parts of the structure and on the position of the inhomogeneity in relation to the sealed structure end. Registration of the positive-negative potentials having a large positive phase should not be considered as an indication of passive properties of the structure.
Gen Physiol Biophys 1988 Aug
PMID:Mathematical modelling of intra- and extracellular potentials generated by active structures with short regions of increased diameter. 318 46

Series resistance artifacts in ionic current measurements on single myelinated nerve fibres are commonly minimized by reducing sodium currents. Doing this some deviations from the predictions of the Hodgkin-Huxley-Frankenhaeuser formalism become evident. In the present investigation two methods to reduce sodium currents were used with and without compensated feedback to examine the influence of the nodal series resistance. Changing the availability of sodium permeability by appropriate prepulses peak sodium current-voltage relations obeyed the Hodgkin-Huxley-Frankenhaeuser formalism only provided the amount of compensated feedback was set to give minimum of the current-voltage relation near E = 0. For reduced sodium concentration in the bathing fluid the so-called independence principle predicts a shift of the minimum of the current-voltage relation on the potential axis in negative direction as compared to ordinary Ringer solution, if the effective series resistance is sufficiently small. This was confirmed by experiments only if the above mentioned amount of compensated feedback was used. The results suggest that the "E = 0"-criterion indicates optimum compensation of the influence of the series resistance.
Gen Physiol Biophys 1988 Apr
PMID:Minimizing the influence of the series resistance in potential clamped Ranvier nodes. 339 97

Membrane potential and current were studied in cut end fibres of frog skeletal muscle under current and voltage clamp conditions, by the double sucrose gap technique. Similar action potentials were recorded under current clamp conditions with either the microelectrode or the double sucrose gap techniques. Under voltage clamp conditions, the control of the membrane potential was maintained adequately. The early current was sensitive to both TTX and external Na concentration suggesting that the current was carried by Na ions. Sodium current (INa) was subsequently analysed using the Hodgkin-Huxley formulae. INa half-activation and inactivation occurred at -34 mV and -60 mV, respectively. Na-rich solution applied internally by diffusion through cut ends produced a reduction of INa associated with a shift of the sodium current reversal potential (VNa) towards more negative membrane potentials. This suggested that the sodium electromotive force was reduced by the increase in internal Na content of the fibre. Iodate applied externally changed neither the activation nor the inactivation time courses of INa, but reduced the peak current. Conversely, internally applied by diffusion from the cut end of skeletal muscle fibre, iodate slowed down the time course of INa inactivation and decreased the current peak. In conclusion, the double sucrose gap technique adapted to cut end frog skeletal muscle fibre allows a satisfactory analysis of INa.
Gen Physiol Biophys 1987 Aug
PMID:Voltage-clamp of cut-end skeletal muscle fibre: a diffusion experiment. 349 62

A mathematical model developed in our laboratory is used to estimate and analyse extracellular potentials generated in a volume conductor by a geometrically inhomogeneous structure with a step increase or a step decrease in its diameter. The transmembrane potentials were calculated using the model of Hodgkin and Huxley (1952) and the method of Joyner et al. (1978). Variations in waveforms of the transmembrane and extracellular potentials were described and discussed. Differences in waveforms of the extracellular potentials and in declines of their components are due to changes in the source which generates these potentials. In case of a propagation block the peak-to-peak amplitude of the extracellular potentials calculated over the area of the block may be higher than that over the area of propagation of action potentials. The possible applications of the results to the analysis of extracellular potentials recorded around actual motoneurons during their orthodromic or antidromic activation are discussed.
Gen Physiol Biophys 1987 Feb
PMID:Mathematical modelling of intra- and extracellular potentials generated by active structures: effects of a step change in structure diameter. 359 23

Eel electroplaques provide experimental conditions in which registration of phase plane trajectories (dV/dt vs. V) and impedance measurements with an AC Wheatstone bridge, in conjunction with spike electrogenesis describe quantitatively the ionic processes of the electrogenesis. Thus, these data employing as they do measurements of transients, permit an independent test of the validity of the assumptions which underlie the Hodgkin-Huxley equivalent circuit: independent ionic channels with fixed ionic batteries and exhibiting time-variant conductance changes with different kinetics for the different channels. The analysis accords with earlier findings on voltage-clamped electroplaques and this agreement confirms the validity of the equivalent circuit despite the fact that the current-voltage characteristics of the axons and electroplaques differ profoundly. As for squid axons, the equivalent circuit of the electroplaques has four branches: a capacity and three ionic channels. One of the latter is an invariant leak channel (G(L)) of high conductance. A K channel (G(K)) is fully open at rest, but rapidly undergoes inactivation when the cell is depolarized by more than 40 mv. G(L) and G(K) have a common inside negative emf (E(K)). A Na channel (G(Na)) with an inside positive emf (E(Na)) is closed at rest, but opens transiently upon depolarization.
J Gen Physiol 1968 Jul
PMID:Analysis of spike electrogenesis of Eel electroplaques with phase plane and impedance measurements. 431 47

The permeability of K channels to various cations is studied in myelinated nerve. Ionic currents under voltage clamp are measured in Ringer solution containing tetrodotoxin and a high concentration of the test ion. Reversal potentials for current in K channels are determined and used with the Goldman-Hodgkin-Katz equation to calculate relative permeabilities. The ratios P(Tl):P(K):P(Rb):P(NHNH4) are 2.3:1.00:0.92:0.13. No other ions are found to be measurably permeant including Li(+), Na(+), Cs(+), methylamine, guanidine, hydrazine, or hydroxylamine. The ratio P(Na)/P(K) is less than 0.01. Potassium conductance is depressed at pH values below 5.0. Leakage conductance is higher in K, Rb, Cs, NH(4), and Tl Ringer than in Na Ringer, but the selectivity sequence probably is not the same as for K channels. The hypothesis is offered that the narrowest part of the K channel is a circle of oxygen atoms about 3 A in diameter with low electrostatic field strength.
J Gen Physiol 1973 Jun
PMID:Potassium channels in myelinated nerve. Selective permeability to small cations. 454 Oct 77

Contractile activation was studied in frog single muscle fibers treated with tetrodotoxin to block action potentials. The membrane potential in a short segment of the fiber was controlled with a two-electrode voltage clamp, and the contractile response of superficial myofibrils in this segment was observed microscopically. The strength-duration relation for contractile activation was similar to that reported by Adrian, Chandler, and Hodgkin (1969); at 3.9 degrees C, the contraction threshold was -44 mV for long depolarizing pulses (100-ms) and increased to +64 mV for 2-ms depolarizations. Hyperpolarizing postpulses shifted the threshold for 2-ms pulses to more positive values, and a similar, but smaller, effect was produced by hyperpolarizing prepulses. The decay of excitability following subthreshold pulses showed two apparently distinct components; at 3.9 degrees C, excitability fell to 50% of its initial value within 4 ms, while the subsequent decline of excitability proceeded with a half-time of about 20 ms.
J Gen Physiol 1974 Jun
PMID:Contractile activation in frog skeletal muscle. 454 89


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>