A. R. Gardner-Medwin

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Equations are derived for potassium (K+) dynamics in simplified models of brain tissue. These describe K+ movement in extracellular space, transfer of K+ associated with current flow through cells (the so-called spatial buffer mechanism) and equilibration between extracellular space and cytoplasm. Numerical calculations show that the principal data on K+(More)
The aim of this study was to identify the principal factors that determine the time course of force and power output by muscle during patterns of stimulation and movement similar to those during fish swimming. Fully activated, white muscle fibres isolated from dogfish Scyliorhinus canicula were used to characterize the force-velocity relationship of the(More)
Ion-selective micro-electrodes have been used to measure K+ and Ca2+ activity changes in extracellular space beneath the surface of the neocortex and cerebellar cortex during current flow across the tissue surface in anaesthetized rats. Inward currents produced decreases of [K+]o and outward currents produced increases, with insignificant changes in(More)
A new concept, that of "buffer capacity," is defined for potassium-buffering mechanisms in neural tissue. Buffer capacities for different mechanisms can be added and compared, thus simplifying quantitative assessment of diffusion, cytoplasmic uptake, and spatial buffering under varied conditions. The characteristic frequency components for potassium(More)
The flux of K+ produced by electric current across the pia-arachnoid surface of the neocortex of anaesthetized rats has been studied with K+-selective electrodes in a cup at the surface and with flame photometry. The potential differences developed across three regions of the rat brain (neocortex, cerebellum, hippocampus) have been measured as [K+] was(More)
The membranes of glial cells are highly selectively permeable to potassium. The implications of this and the possible reasons for it are discussed. Glial cells may contribute to buffering the extracellular K+ concentration of brain tissue through several mechanisms. However, the only one that benefits from the K+ selective permeability is the so-called(More)
Gradient echo magnetic resonance (MR) imaging was used to demonstrate propagating waves of cortical spreading depression (SD) in the anaesthetised rat. SD was initiated by remote perfusion with 150 mM KCl applied for 0.5-2 min to the left parietal cortex. Gradient echo MR images were obtained every 12-30 s in either a vertical coronal section or a(More)
The apparent diffusion coefficient (ADC) and relaxation times of water were measured by magnetic resonance imaging (MRI) in the isolated turtle cerebellum during osmotic cell volume manipulation. The aim was to study effects of cell volume changes, a factor in ischemia and spreading depression, in isolation from considerations of blood flow and metabolism.(More)
Magnetic fields were measured with SQUID magnetometry outside the skull of anaesthetised rabbits during initiation and propagation of spreading depression (SD) in the cortex. Slowly changing fields (up to 1.4 pT) were observed during the propagation phase, from 4-8.5 min after initiation of SD with KCl application, with maxima at about 6 min. The peak(More)