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Biomedical subjects

T Brismar

Publications and source records attributed to T Brismar.

At least 73 records · Page 4Linked to original sources
PubMed1983

C-11-labeled glucose and its utilization in positron-emission tomography.

Carbon-11-labeled glucose was prepared photosynthetically using the green alga Scenedesmus obtusiusculus Chod. The carbohydrates were extracted from the cells with dilute HCI and the glucose was isolated and purified using high-performance liquid chromatography. The manipulations in the hot cell are described. Analysis of the material (gas liquid chromatography and HPLC) showed that the glucose obtained was radiochemically pure. The total incorporation of the 11CO2 added to the algae was 60-80%. The radiochemical yield of pure carrier-added glucose was approximately 25%, at 40 min after E.O.B. including the HPLC purification and sterile filtration. The C-11 glucose uptake in rat brain was compared with that of commercial D[U-14C]glucose, and preliminary PET studies with D-[11C]glucose in a patient with a brain infarct are presented.

Animals↗
PubMed1982

Potassium permeability in thin amphibian myelinated fibres.

Potential clamp analysis of thin (10-12 micrometers) myelinated fibres from amphibia (Xenopus laevis and Rana temporaria) showed that they had a large delayed K-permeability (PK) and a PK/PNa-ratio of 0.32, which is similar to the ratio in large (25-30 micrometers) frog fibres. These results agree with earlier evidence of a large delayed PK in 10-15 micrometers Rana fibres; a recent description of a size-dependent difference in PK was thus not confirmed. The large PK (0.32 cm3s-1 X 10(-9) in 10-12 micrometers amphibian fibres contrasted with the small PK (0.05 cm3 s-1 X 10(-9) in 12 micrometers rat fibres. Frog and toad fibres also had a larger nodal capacitance (4 pF), but smaller leak conductance (18 nS) than rat fibres (1.4 pF and 29 nS). These differences may be related to the morphological evidence of a more open node with a larger surface area in the amphibian as compared to the rat node.

Animals↗
PubMed1981

Electrical properties of isolated demyelinated rat nerve fibres.

Isolated large rat nerve fibres with diphtheria toxin induced paranodal demyelination were investigated. These fibres had increased membrane time constant of the demyelinated nodal segment, related to a large increase in capacitance (5 to 50 times). The resting conductance was less increased (2 to 3 times), meaning that the internodal axolemma has considerably higher resting resistance than the nodal membrane. A large variation in action potential amplitude was found which was unrelated to the size of the nodal widening and the passive electrical properties.

Action Potentials↗
PubMed1981

Specific permeability properties of demyelinated rat nerve fibres.

The specific permeability properties of isolated rat fibres with diphtheria toxin induced paranodal demyelination were investigated in potential clamp experiments. Nodal widening (4 to 6 micrometers) and paranodal demyelination (20 to 90 micrometers) were associated with a very large increase in the normally low delayed K-permeability (greater than 10 times). The resting K-permeability (which was comparatively large in the rat fibres) was similarly increased, which decreased action potential amplitude and excitability. Fibres with paranodal demyelination had, in addition, a large increase in the maximum peak Na-permeability (2 to 5 times the normal), which indicated that excitability was upheld by formation of new Na-permeability sites. The conduction defects in demyelinated fibres can therefore not be related to the size of the demyelination, but to the specific permeability changes in the demyelinated segment.

Action Potentials↗
PubMed1981

Changes in nodal function in nerve fibres of the spontaneously diabetic BB-Wistar rat: potential clamp analysis.

Single myelinated nerve fibres were isolated from the sciatic nerves of the spontaneously diabetic BB-Wistar rat after 17-185 days of overt diabetes. Pronounced demyelination and paranodal changes were found in one rat (diabetes duration 185 days), the others had no structural changes that could be detected light-microscopically. Potential clamp analysis of these fibres showed a decreased Na equilibrium potential (UNa), decreased Na currents caused by large inactivation, and a specific increase in the K-permeability. Measurements with high-K solution outside the node revealed that the decreased UNa was caused by high axoplasmic [Na]. Fibres with increased K-permeability had, in addition, increased nodal leak conductance. Decreased excitability was found in the majority of the fibres and was related to the permeability changes. The present findings indicate that axonal dysfunction (Na-accumulation and inactivation of the Na-permeability) precede the changes (increased K-permeability) related to paranodal demyelination.

Action Potentials↗
PubMed1980

Analysis of peripheral nerve function in streptozotocin diabetic rats.

Conduction velocity of rat sciatic nerve, estimated both in vivo and in vitro, did not change during 2--21 weeks following induction of diabetes by injection of streptozotocin. During this period blood sugars were in the range 17.6--30.4 mM and symptoms of uncontrolled diabetes were noted. The failure of velocity to decrease contrasts strongly with several previous reports, while the failure to increase with age may be explained with the aid of published morphometric data. Experiments on nerve fibers isolated from streptozotocin-diabetic rats rats confirmed that the nerve function was normal in respect of action and resting potential. Potential clamp analysis of nodal membrane similarly indicated that these fibres had normal permeability properties.

Animals↗
PubMed1980

The effect of divalent and trivalent cations on the sodium permeability of myelinated nerve fibres of Xenopus laevis.

The effect of external Ca, Mg, Sr, Ba and La concentration was studied in potential clamp experiments on single myelinated nerve fibres of the frog (Xenopus laevis). An increase in cationic concentration caused a positive shift of the Na permeability (PNa) curve along the potential axis, a decrease in max. PNa and a decrease in the slope of the PNa curve. The effectiveness of Mg, Sr and Ba was similar and about 0.6 compared to that of Ca, whereas La was about 80 times more effective than Ca.

Animals↗
PubMed1980

Potential clamp analysis of membrane currents in rat myelinated nerve fibres.

1. Large myelinated nerve fibres were isolated from rats and the membrane action potential was recorded in single nodes of Ranvier. Potential clamp experiments were performed at 24 degrees C and in one fibre also at 33 degrees C. 2. Positive potential steps were associated with an initial, mainly Na carried, current with an equilibrium potential (Ue) of 40 +/- 13 mV. The INa vs. U curve showed rectification at large positive potentials. 3. The Na permeability (PNa) curve was characteristically S-shaped with a half value at -48 +/- 6 mV and a ceiling value of 3.7 +/- 0.7 cm.sec-1.10(-3). PNa as defined by the constant field equation accounted for the rectification of the INa/U curve. 4. The potential and time dependence of the rapid inactivation (h) process was described quantitatively in terms of its steady state (h infinity) vs. U curve and its rate constants (alpha h and beta h) vs. U curves. h infinity (U = -80 mV) was 0.68 +/- 0.09. 5. The delayed currents were small and the ionic specificity of the delayed permeability changes was not identified. Tentatively calculated PK at large potentials was 0.21 +/- 0.06 cm.sec-1.10(-3). The leak conductance (gL) was 130 +/- 33 mS.cm-2. 6. A temperature rise in one experiment from 24 to 33 degrees C increased the rate constants (alpha h and beta h), but did not significantly change the size of the delayed currents. 7. INa was completely blocked by 25 nM-TTX in the outside solution. External application of 5 mM-TEA only slowly and incompletely blocked the small delayed currents. This effect was not fully reversible. 8. A comparison with frog fibres showed that the node in rat fibres had (a) a lower Ue of the initial current (probably because of a lower Na selectivity of the channel for the initial current), (b) approximately equal max. peak PNa, (c) about 10 mV negatively shifted PNa vs. U and h infinity vs. U curves, (d) quantitatively similar relations between rate constants of inactivation (alpha h and beta h) and U at 20--24 degrees C, (e) PK that was 1/5 of PK in frog fibres, (f) 4--5 times larger leak conductance, (g) membrane action potentials of smiliar amplitude and duration.

Animals↗
PubMed1978

Effect of the nonionic detergent triton X-100 on sodium permeability of the myelinated nerve fibre of Xenopus laevis.

The effect of the nonionic detergent Triton X-100 (TX-100) on the Na permeability (PNa) properties of the nodal membrane in myelinated nerve fibres of Xenopus laevis was analysed with potential clamp technique. Application of TX-100 caused a rapid initial decrease in PNa that was reversible at wash out as well as a slow irreversible block. Both effects dependend on [TX-100] and duration of exposure. The reversible reduction of PNa at the steady state was 50% at 40--60 micrometer TX-100. The slope of the Hill plot for the reaction was 1.75 indicating a deviation from a first order reaction. The equilibrium dissociation constant (KD) for n = 1.75 was 0.9 X 10(-7) (M1.75). KD calculated from the rate constants for onset and offset of the reversible reaction (KD = k2/k1) was 1.5 X 10(-7) (M1.75). The possibility that the action of TX-100 involves membrane proteins is discussed.

Animals↗
PubMed1977

Slow action of Ca on myelinated nerve fibres of Xenopus laevis.

Single myelinated nerve fibres were isolated and the nodal currents were recorded with potential clamp technique. Rapid solution changes were performed by use of a recording chamber so shaped that it had a minimal dead space. A volume ten times larger than the dead space flowed past the node within about 20 ms. The half-time of the change in Na current (INa)amplitude associated with changes between solutions of different [Na]:s was 100-150 ms, whereas the half-time of the change in INa associated with changes between solutions of different [Ca]:s was 200-300 ms. The external [Ca] affects INa through its action on the Na permeability properties of the nodal membrane. The difference in rate of effect between changes in [Na] and [Ca] was also noticeable when simultaneous changes were performed. These findings are discussed with regard to the properties of the nodal gap.

Animals↗
PubMed1977

Slow mechanism for sodium permeability inactivation in myelinated nerve fibre of Xenopus laevis.

1. Single myelinated nerve fibres were isolated and the nodal currents were recorded under potential clamp conditions. The effect of membrane potential on the Na permeability (PNa) mechanism was analysed. 2. The available PNa increased slowly during negative polarization of the membrane. The time course of this change was about 10(3) times slower than the time course of the mechanism for the usual PNa inactivation (h-system). The slow PNa changes could be distinguished from changes in h because of the difference in rate. 3. The slow PNa variation was independent of the state of the h-system and was largely due to a slow inactivation system, which empirically could be described as separate from the other permeability variables. 4. In the steady state the slow inactivation appeared almost absent at a holding potential of -120 mV, whereas it was 30% complete at the resting potential (-70 mV) and 80% complete at a holding potential of -20 mV. 5. Changes in the slow inactivation system showed an approximately exponential time course. At 10-12 degrees C the time constant was about 3 sec with U = -70 mV, 7 sec with U = -100 mV and 1-5 sec with U = -127 mV. 6. High Ca shifted the steady state slow inactivation curve in the positive direction along the potential axis.

Animals↗