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Query: UMLS:C0019829 (Hodgkin's disease)
 30,247 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The anatomy and physiology of the Drosophila larval neuromuscular junction were studied. 2. The dependence of muscle resting potentials on [K+]o and [Na+]o follows the Goldman-Hodgkin-Katz equation (PNa/PK=0-23). Chloride ions distribute passively across the membrane. 3. The mean specific membrane resistance of muscle fibres is 4-3 X 10(3) omega cm2, and the mean specific membrane capacitance is 7-1 muF/cm2. The muscle fibre is virtually isopotential. 4. Transmitter release is quantal. Both the miniature excitatory junctional potential and the evoked release follow the Poisson distribution. 5. Transmitter release depends on approximately the fourth power of [Ca2+]o. If Sr2+ replaces Ca2+, it depends on approximately the fourth power of [Sr2+]o. Mg2+ reduces transmitter release without altering the fourth power dependence on [Ca2+]o.
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PMID:Properties of the larval neuromuscular junction in Drosophila melanogaster. 1 39

1. The ionic dependence of current through the 3',5'-cyclic guanosine monophosphate (cyclic GMP)-activated channels of salamander rods was studied in excised inside-out membrane patches from isolated outer segments. Voltage-clamp experiments on transducing rods were performed so that the channels in intact cells could be compared with those in excised patches. 2. The reversal potential of the cyclic GMP-induced patch current was close to the Na+ equilibrium potential when the concentration of NaCl on the cytoplasmic surface of a patch was varied at constant external NaCl concentration. Fitting the Goldman-Hodgkin-Katz equation indicated that the apparent ratio of permeabilities for Na+ and Cl- was at least 50. This confirms a previous report that the channel's Na+ permeability is much larger than its Cl- permeability. 3. Na+ currents through the channel did not obey the independence principle. The outward patch current at large positive potential began to saturate with increasing concentrations of internal Na+, as if permeation required Na+ to bind to a site with an apparent dissociation constant around 180 mM. 4. In symmetrical NaCl solutions containing very low concentrations of divalent cations the current-voltage relation measured from excised patches 50 microseconds after switching the voltage showed mild outward rectification. By 1 ms the rectification was more pronounced. The rectification at 50 microseconds is attributed to voltage dependence of Na+ permeation. The additional rectification at later times is attributed to voltage dependence of the channel's probability of being open, depolarization favouring the open state. 5. In symmetrical Mg2+ solutions the cyclic GMP-induced patch currents were smaller and the outward rectification was more pronounced. 6. Addition of Mg2+ or Ca2+ to an internal Na+ solution blocked the cyclic GMP-induced Na+ current through the channels, as if by occupying a single binding site with an affinity in the 0.1-2 mM range. Block by Mg2+ was voltage dependent, suggesting that the binding site was within the channel's transmembrane electric field. Raising the Mg2+ concentration on the external surface of the patch increased the apparent dissociation constant of block by internal Mg2+, as expected if external and internal Mg2+ compete for the same binding site. 7. Block by internal Ca2+ had an opposite and weaker voltage dependence than block by internal Mg2+. 8. In symmetrical solutions containing both Na+ and Mg2+ the outward rectification was more pronounced than in solutions containing Na+ alone. In solutions thought to be close to physiological the outward patch current increased e-fold for a depolarization of 24-30 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Cation interactions within the cyclic GMP-activated channel of retinal rods from the tiger salamander. 138 54

1. The effects of amiloride on the membrane potential of frog skeletal muscle fibres were investigated with a single intracellular microelectrode. Two microelectrode current- and voltage-clamp experiments were also performed to determine the effects of amiloride on the electrical constants and membrane current near the resting potential. 2. Amiloride reversibly hyperpolarized muscle fibres up to ca 12 mV in 2.5 mM-K+, in a concentration-dependent manner, with a half-maximum effect at 0.2 mM. Amiloride (0.4 mM) also significantly increased the membrane resistance of muscle fibres. 3. The effects of amiloride were consistent with the classical theory of the resting potential and could be described by assuming that it removes the Na+ permeability factor in the Goldman-Hodgkin-Katz equation for [K+]o > or = 2.5 mM. 4. Replacement of [Na+]o by N-methyl-glucamine, choline or Mg2+ produced smaller effects on the resting potential and on membrane resistance than those induced by amiloride. 5. It is concluded that an amiloride-sensitive poorly selective conductance continuously depolarizes the cellular membrane thus playing a role in the resting potential of frog skeletal muscle.
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PMID:The effect of amiloride on the resting potential and the electrical constants of frog skeletal muscle fibres. 166 56

Reverse transcriptase (RT) transcribes viral RNA into DNA to be integrated into the host genome. To study epidemiological aspects of human leukemias and lymphomas which are known to express retroviruses, clinical specimens in this report were assayed for divalent cation-dependent viral-specific RT. The assay was carried out with cells solubilized with a detergent to release RT enzyme. RT was purified with poly(U)-Sepharose which fixed all DNA polymerases and assayed with 4 synthetic homopolymers, oligonucleotide primed-templates, poly(rA)-oligo(dT)12-18 or poly(dA)-oligo(dT)12-18 with Mg2+, poly(rC)-oligo(dG)12-18 or poly(rCm)-oligo(dG)12-18 with Mn2+ as divalent cation and [methyl-3H]thymidine 5'-triphosphate or deoxy[8-3H]guanosine 5-triphosphate respectively. Radioactivity incorporation of the precipitate allows quantitation of RT activity. One Hodgkin's disease, one out of 2 B lymphomas, one out of 2 T lymphomas, eight out of 12 leukemias were found to be positive for RT activity as well as acquired immunodeficiency syndrome (AIDS) patients, known to express RT. The obtained RT activity in hematological malignancies was found to be comparable to positive controls such as RT enzymes purified from avian myeloblastosis and Moloney murine leukemia viruses.
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PMID:Presence of reverse transcriptase in human leukemias and lymphomas. 170 70

1. Macroscopic and single-channel currents through several types of cloned rat brain Na+ channels, expressed in Xenopus oocytes, were measured using the patch-clamp technique. 2. For all cloned channel types and for endogenous Na+ channels in chromaffin cells, intracellular Mg2+ blocks outward currents in a voltage-dependent manner similar to that in rat brain type II Na+ channel (Pusch et al. 1989). 3. A sodium-channel mutant ('cZ-2') with long single-channel open times was used to examine the voltage-dependent reduction of single-channel outward current amplitudes by intracellular Mg2+. This reduction could be described by a simple blocking mechanism with half-maximal blockage at 0 mV in 1.8 mM intracellular Mg2+ and a voltage-dependence of e-fold per 39 mV (in approximately 125 mM [Na]i); this corresponds to a binding-site at an electrical distance of 0.32 from the inside of the membrane. 4. At low Mg2+ concentrations and high voltages, the open-channel current variance is significantly elevated with respect to zero [Mg]i. This indicates that Mg2+ acts as a fast blocker rather than gradually decreasing current, e.g. by screening of surface charges. Analysis of the open-channel variance yielded estimates of the block and unblock rate constants, which are of the order of 2.10(8) M-1 S-1 and 3.6.10(5) S-1 at 0 mV for the mutant cZ-2. 5. A quantitative analysis of tail-currents of wild-type II channels showed that the apparent affinity for intracellular Mg2+ strongly depends on [Na]i. This effect could be explained in terms of a multi-ion pore model. 6. Simulated action potentials, calculated on the basis of the Hodgkin-Huxley theory, are significantly reduced in their amplitude and delayed in their onset by postulating Mg2+ block at physiological levels of [Mg]i.
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PMID:Open-channel block of Na+ channels by intracellular Mg2+. 217 Jan 2

1. Intracellular recordings were made from locus coeruleus (LC) neurones in a totally submerged brain slice preparation from adult rats. The effect of gamma-aminobutyric acid (GABA) on LC neurones was studied under current-clamp and voltage-clamp conditions. GABA caused inhibition of spontaneous firing and a large conductance increase in LC neurones. These effects could be accompanied by depolarization, hyperpolarization or little change in membrane potential depending on the presence or absence of Cl- in the recording microelectrode. 2. The reversal potential for GABA-induced changes in membrane potential (EGABA) was -71.3 +/- 1.1 mV (S.E.M., n = 21) in cells impaled with potassium acetate electrodes and -47.5 +/- 1.4 mV (S.E.M., n = 15) in cells impaled with KCl electrodes. When the external Cl- concentration was reduced EGABA was shifted in the depolarizing direction by 51.5 mV per tenfold change in external Cl- which is close to the shift predicted by the Nernst equation for a selective increase in CL- conductance. 3. GABA effects on LC neurones result from a direct action since they persist in low-Ca2+ and high-Mg2+ media which block synaptic transmission. 4. The effects of GABA were concentration dependent and antagonized by bicuculline (10 microM) and bicuculline methiodide (80-100 microM) indicating that they were mediated predominantly by an action on GABAA receptors. In the presence of bicuculline, EGABA was shifted towards the K+ equilibrium potential which indicated a residual bicuculline-resistant action at GABAB receptors. 5. GABA-induced responses were membrane potential dependent. GABA conductance was observed to decrease with membrane hyperpolarization in a linear manner. GABA-induced current showed outward rectification. In the voltage range studied (rest to -110 mV) the extent of this rectification was predicted by the Goldman-Hodgkin-Katz equation, suggesting that it was due to the unequal distribution of Cl- across the membrane. In addition, the time constant of decay of GABA current was decreased by membrane hyperpolarization; this could be due to a voltage-dependent change in receptor or channel kinetics. 6. These data suggest that the primary action of GABA on LC neurones is to increase Cl- conductance by activation of bicuculline-sensitive GABAA receptors. Due to the voltage dependence of GABA responses, GABA will exert a stronger inhibitory effect on LC neurones at depolarized than at hyperpolarized membrane potentials. This could serve as a negative feedback mechanism to control excitability of these neurones.
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PMID:gamma-Aminobutyric acid responses in rat locus coeruleus neurones in vitro: a current-clamp and voltage-clamp study. 234 90

1. The generation of action potentials elicited from enzymatically dispersed ventricular cells from the frog, Rana catesbeiana, has been shown to be due to the influx of both Na+ and Ca2+. The maximum rate of rise, the amplitude and the duration at 50% repolarization of the action potential were estimated to be 26.4 +/- 5.1 V/s (n = 8), 110 +/- 2.7 mV (n = 8) and 601 +/- 180 ms (n = 8) at 15 degrees C, respectively. 2. Inward Na+ current (INa) was studied in these ventricular cells by the whole-cell patch clamp technique in a medium where Ca2+ current was eliminated by substituting extracellular Mg2+ for Ca2+ and K+ current was suppressed by applying Cs+ intracellularly. All the voltage clamp experiments were carried out at 4 degrees C. 3. INa elicited by single depolarizing steps from a holding potential (VH) of -80 mV had a threshold of -50 mV and was maximal at -20 mV. Peak currents in normal Ringer solution containing 113.5 mM-Na+ were of the order of 0.01-0.02 mA/cm2. Maximum Na+ conductance (gNa) was calculated to be 5.9 mS/cm2. 4. Under normal conditions the reversal potential for INa was determined to be 50 mV, which is close to the value predicted from the Nernst equation. The reversal potential changed by 59 mV per tenfold change in the activity of extracellular Na+ (aNa). 5. The instantaneous relation between INa tail currents and membrane potential is linear, crossing the abscissa at the reversal potential for INa. 6. Reconstructions of INa were made in terms of the parameters of the Hodgkin-Huxley model for the squid axon, using constants obtained from the frog ventricular cells. 7. The falling phase of INa and the development of inactivation measured by the double-pulse method could be well fitted by a single-exponential function. 8. The time course for recovery of INa from inactivation exhibited a single time constant.
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PMID:A study of the electrical characteristics of sodium currents in single ventricular cells of the frog. 245 74

1. Using the method of Hodgkin, McNaughton & Nunn (1985) for rapidly changing the extracellular medium, we analysed the effect of divalent cations on the photocurrent of isolated retinal rods of the tiger salamander. 2. When the extracellular NaCl was replaced by equiosmolar amounts of BaCl2, SrCl2, CaCl2, MgCl2 and MnCl2 the efficacy in carrying the photocurrent at early times was Ba2+ greater than Sr2+ greater than Ca2+ greater than Mg2+ greater than Mn2+. At early times Ba2+ could carry a photocurrent similar to or larger than that carried by Na+. 3. The photocurrent carried by Ba2+ increased by about 50% when [Ca2+]o was reduced from 1 to 0.1 mM. In the presence of 0.1 mM-Ca2+ in the extracellular medium the photocurrent carried by Ba2+ saturated when [Ba2+]o was close to 50 mM and was half-activated at 15 mM [Ba2+]o. 4. The photocurrent which can be carried by Sr2+ is not larger than that carried by Ba2+ and does not saturate for [Sr2+]o up to 70 mM. 5. When extracellular Na+ is replaced by the impermeant organic ion choline it is possible to observe a transient photocurrent which is carried by Ca2+. This current has a maximal value of about 11 pA and has a half-activation constant of about 50 microM. 6. Movements of Mg2+ across the light-sensitive channel can be seen only when extracellular Ca2+ is reduced below 10 microM. Under these conditions the maximal photocurrent which can be carried by Mg2+ at early times is about 8 pA and has a half-activation of about 2 mM. Under normal conditions Mn2+ is hardly permeable through the light-sensitive channel. 7. It is concluded that the selectivity of the light-sensitive channel in the low ionic concentration range is Ca2+ greater than Sr2+ greater than Ba2+ greater than Mg2+ greater than Na+.
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PMID:The ionic selectivity of the light-sensitive current in isolated rods of the tiger salamander. 246 83

1. By using the method of Hodgkin, McNaughton & Nunn (1985) for rapidly changing the extracellular medium, we analysed the effect of the organic compound IBMX (3-isobutyl-1-methylxanthine) on the movement of divalent cations through the light-sensitive channels of isolated retinal rods of the tiger salamander. 2. When the rod is treated with 0.5 mM-IBMX it is possible to observe photocurrents larger than 50 pA carried by Ba2+, Sr2+, Ca2+, Mg2+ and Mn2+. Under these conditions Ca2+, Mg2+ and Mn2+ carry photocurrents of similar amplitude, while Ba2+ and Sr2+ usually carry larger photocurrents. 3. The movement of Mn2+ through the light-sensitive channel, which is hardly detected under normal conditions, can also be observed after treating the rod for a few seconds with a solution containing 35 mM[Na+]o and 10(-7) M[Ca2+]o. Under these conditions the photocurrent carried by Mn2+ is fully saturated in the presence of 1 mM-extracellular Mn2+. 4. When the rod is pre-treated with an extracellular solution containing 0.5 mM-IBMX the maximal photocurrent which can be carried by 10 mM [Ca2+]o increases from about 10 pA to approximately 200 pA. In these conditions the half-activation of the Ca2+ current is between 1 and 10 mM, that is 20-50 times higher than in normal conditions (Menini, Rispoli & Torre, 1988). 5. When the rod is pre-treated with an extracellular solution containing 0.5 mM-IBMX the half-activation of the photocurrent which can be carried by Mg2+, Ba2+ and Sr2+ is equivalent to or greater than 10 mM. In the absence of pre-treatment with IBMX the half-activation of the photocurrent carried by Mg2+, Ba2+ and Sr2+ is less than 5 mM. 6. We conclude that the light-sensitive channel can exist in at least two distinct open states. The selectivity of the channel in the first open state is as described in a previous paper (Menini et al. 1988). Mn2+, which is hardly permeable through the light-sensitive channel in the first open state, can move through the light-sensitive channel in the second open state. Ca2+, Mg2+, Ba2+ and Sr2+ permeate more freely through the light-sensitive channel in the second open state, probably because the electrostatic interactions between these ions and the channel are less strong.
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PMID:The modulation of the ionic selectivity of the light-sensitive current in isolated rods of the tiger salamander. 247 69

Ca2+ inward currents evoked by membrane depolarization have been studied by the intracellular dialysis technique in the somatic membrane of isolated dorsal root ganglion neurones of new-born rats. In about 20% of the investigated cells a hump has been detected on the descending branch of the current-voltage curve, indicating the presence of two populations of Ca2+ channels differing in their potential-dependent characteristics. An initial less regular component of the Ca2+ current was activated at membrane potentials from -75 to -70 mV. Its amplitude reached 0.2-0.9 nA at 14.6 mM-extracellular Ca2+. The activation kinetics of this component could be approximated by the Hodgkin-Huxley equation using the square of the m variable. tau m varied in the range from 8 to 1 ms at potentials between -60 and -25 mV ('fast' Ca2+ current). The second component of the Ca2+ current was activated at membrane depolarizations to between -55 and -50 mV. It could be recorded in all cells investigated and reached a maximum value of 1-7 nA at the same extracellular Ca2+ concentration. This component decreased rapidly during cell dialysis with saline solutions. The decrease could be slowed down by cooling and accelerated by warming the extracellular solution. Intracellular introduction of 3',5'-cAMP together with ATP and Mg2+ not only prevented the decrease but often restored the maximal current amplitude to its initial level. The activation kinetics of this component could also be approximated by a square function, tau m being in the range 16-2.5 ms at membrane potentials between -20 and +3 mV ('slow' Ca2+ current). The fast Ca2+ current inactivated exponentially at sustained depolarizations in a potential-dependent manner, tau h varying from 76 to 35 ms at potentials between -50 and -30 mV. The inactivation of the slow Ca2+ current studied in double-pulse experiments was current-dependent and developed very slowly (time constant of several hundreds of milliseconds). It slowed down even more at low temperature or after substitution of Ba2+ for Ca2+ in the extracellular solution. Both currents could also be carried by Ba2+ and Sr2+, although the ion-selecting properties of the two types of channels showed quantitative differences. Specific blockers of Ca2+ channels (Co2+, Mn2+, Cd2+, Ni2+ or verapamil) exerted similar effects on them. The existence of metabolically dependent and metabolically independent Ca2+ channels in the neuronal membrane and their possible functional role are discussed.
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PMID:Two types of calcium channels in the somatic membrane of new-born rat dorsal root ganglion neurones. 258 15


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