Excitability changes reveal decreased sodium permeability in neuropathy.

Nerve excitability was tested in isolated sciatic nerves of rats with acute uremia. Larger than normal stimulating pulses were required to elicit a maximal compound potential, whereas the relative refractory period was unaffected. The threshold range, relative to the absolute threshold, was a good measure of the decreased excitability and may be a useful clinical method.

Experimental uremic neuropathy. Part 1. Decreased nerve conduction velocity in rats.

Acute and chronic renal failure were induced in adult male albino rats by conventional surgical methods. The glomerular filtration rate of rats with chronic uremia was reduced to approximately 15% of normal. Despite this drastic degree of renal failure, the motor nerve conduction velocity (MCV) increased from 47.

Experimental uremic neuropathy. Part 2. Sodium permeability decrease and inactivation in potential clamped nerve fibers.

Potential recordings and potential clamp of isolated myelinated fibers from the sciatic nerve of acutely uremic rats showed a marked decrease in excitability related to a decrease in the specific Na permeability (P Na) of the nodal membrane. Mean value of the available P Na in the resting node of the uremic rats was 24% of the P Na in a control group. This change explained the decreased nerve conduction velocity in the acutely uremic rat.

Neuropathy-functional abnormalities in the BB rat.

The spontaneously diabetic rat gets a decreased motor-nerve conduction velocity after the onset of diabetes as compared with age- and weight-matched controls. This finding has indicated that these rats develop a neuropathy; but morphological investigations have failed to show structural abnormalities that could explain the decrease in conduction velocity. Measurements of the nervous function revealed a decreased excitability of isolated fibers from sciatic nerves of rats with diabetes duration ranging from 18 days to 6 months.

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.

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.

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.

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.

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.

Confusion, myoclonus and speech arrest: epileptic manifestations after metrizamide myelography.

The importance of accurate diagnosis of epileptic manifestations, even if unusual, as complications of diagnostic metrizamide exploration of the CSF space is emphasized on the basis of 2 case histories.

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.

Convulsants (benzylpenicillin and pentylenetetrazol) on potential clamped myelinated axons from the rat.

The effect of two convulsants, benzylpenicillin and pentylenetetrazol, was tested in potential clamp experiments on single rat myelinated nerve fibres. 10 mM concentrations did not affect the permeability properties of the nodal membrane. The convulsive action is therefore probably not mediated through changes in the excitability of central axons.

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.

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.

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.

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.

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.

Effects of ionic concentration on sodium permeability properties of myelinated nerve fibres of Xenopus laevis.

1. The nodal currents of single myelinated nerve fibres were recorded under potential clamp conditions, and the effect of [Ca], [Na] and [K] in the external solution on some of the Na permeability properties were analysed. 2.