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Biomedical subjects

B Frankenhaeuser

Publications and source records attributed to B Frankenhaeuser.

16 recordsLinked to original sources
PubMed1982

Inactivation of the potassium transport system of myelinated nerve in the presence of a cyclic ionophore.

A potassium carrying ionophore dicyclohexano-18-crown-6 was found to affect the specific ionic currents in the node of Ranvier. Its presence caused an inactivation of the potassium permeability mechanism and a decrease of the sodium permeability. The rate of inactivation of the potassium permeability depended on crown ether concentration, on membrane potential and on temperature. At large concentrations, the rate of inactivation was of the same order of size as the normal rate of activation. The recovery from the inactivated state was slow, it took a few seconds, and recovery time depended on holding potential. The inactivation was caused by potential steps in positive direction. The uncomplexed crown ether is uncharged and does not move due to a potential gradient. The mechanism by which the crown ether makes the inactivation potential dependent remains obscure. A few other ionophores were tested but they did not affect the membrane currents.

Animals↗
PubMed1976

The effects of neuraminidase and protamine chloride on potential clamp parameters of the node of Ranvier (Xenopus laevis).

The effects of neuraminidase and protamine chloride on the ionic currents associated with step changes in membrane potential were studied. Neuraminidase (a hydrolase which cleaves glycosidically bound sialic acid) had negligible effects on the permeability properties. The polycation protamine chloride decreased the sodium as well as the potassium currents. The sodium equilibrium potential decreased during the experiments which indicates a gain in internal sodium concentration. The analysis showed that the effects on the currents were caused by a decrease of the specific permeability changes. No shift along the potential axis of the potential dependent parameters was observed.

Action Potentials↗
PubMed1975

Steady state current rectification in potential clamped nodes of Ranvier (Xenopus laevis).

The membrane potential in single nodes of Ranvier was changed in rectangular pulse steps while the membrane currents, associated with the potential steps, were measured. Changes were made in the ionic composition of the external and the internal medium. The latter changes were obtained by free diffusion through a cut internode. The steady state currents, described on the basis of potassium and leak permeability, were affected by the solution composition in a characteristic way. Increased inside concentration of sodium and lithium caused a striking rectification of the outward steady state currents at large potential steps. Instantaneous potassium currents in high [K+]o at a second potential step to E approximately equal to minus 80 mV were not affected by [Na+]1. Neither [Na+]o nor [K+]i affected the potential at which this rectification appeared. Increased [K+]o shifted the region for rectification along the potential axis in positive direction. These findings form strict limitations for satisfactory models describing the mechanism for the steady state current in myelinated nerve.

Animals↗
PubMed1975

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. [Ca], [Na] and [K] all affected the position of the steady-state Na inactivation (h) curve on the potential axis. The curve was displaced in positive direction by high ionic concentration. 3. The shift associated to different [Ca] was largest in low [Na] and [K]. Similarly the shift associated to different [Na] and [K] was largest in low [Ca]. 4. The maximum peak sodium permeability (max. peak - PNa) was affected by the [Ca], [Na] and [K]. It was greater in (i) low [Ca], (ii) high ([Na] + [K]) and (iii) high [Na]:[K] ratio. 5. The effect of [Ca] on peak - Na was mainly a consequence of a change in PNa (which is the value of PNa if activation were complete, m = 1, and inactivation fully removed, h = 1).

Animals↗
PubMed1966

Potentiometric measurement of membrane action potentials in frog muscle fibres.

1. A potentiometric method for recording membrane action potentials from small segments of isolated skeletal muscle fibres has been described.2. The value of the method in muscle physiology has been appraised by recording from fast and slow skeletal muscle fibres of the frog under a variety of conditions.3. Artifacts associated with this method have been described and their sources investigated.

Animals↗
PubMedDate not supplied

Non-stationary fluctuation analysis of the Na current in myelinated nerve fibers of Xenopus laevis: experiments and stochastic simulations.

Na current fluctuations under voltage-clamp conditions during pulse steps in the potential range from -65 to -30 mV were measured in myelinated nerve fibers of Xenopus laevis. The covariance functions for four consecutive 1 ms intervals were calculated. The time courses of the covariance functions were well fitted with monoexponential functions with time constants between 0.5 and 3 ms, larger at the end of the pulse and larger at more positive potentials. To analyze the underlying channel kinetics we simulated current fluctuations at a step to -35 mV of eight published Na channel models and calculated corresponding covariance functions. None of the models did explain the experimental fluctuation results. We therefore developed a new Na channel model that satisfactorily described the results. Features that distinguished this model from the other tested ones were a slower deactivation rate, and an inactivation transition directly from a closed state.

Animals↗