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D Geduldig

Publications and source records attributed to D Geduldig.

14 recordsLinked to original sources
PubMed1982

Effects of potassium and chloride on the membrane potentials of P815 mastocytoma tumor cells.

The steady-state transmembrane potentials of P815 mastocytoma cells were recorded when the cells were bathed in salines of different compositions. In the normal growth medium (RPMI 1640 with added fetal calf serum) the mean membrane potential was -8.7 mV (SEM +/- 0.4, n = 22). A family of Tris-buffered salines (TBS), modeled from Dulbecco's modified PBS (289 mosmol, 169 milliionic strength units, pH 7.5), having different K+ and different C1- concentrations, were designed and used to bathe the tumor cells. All of the TBS solutions had constant, but reduced levels of ionized Ca2+. In the absence of external C1-, an increase of external K+ from 2 to 20 mM results in a 5.7 mV depolarization. In the presence of external C1- the same increase in external K+ results in a 2.1 mV depolarization. The presence of 145 mM C1- resulted in a steady-state depolarization (for either level of K) of about 50%. One explanation for these results would be the presence of an inward-going active C1- transport.

Cell Line↗
PubMed1979

A source of large axons for neurophysiology: the North Atlantic squid Illex illecebrosus.

A new axon preparation from the ommastrephid squid (Illex illecebrosusus (Lesueur)) is described. This squid is common in the Northwestern Atlantic and features a number of long, unbranched, and moderately large-diameter axons having no apparent 'twigging.' Although the diameters of these axons are somewhat smaller than those of 'giant' axons coming from some other species of squid, this axon preparation should be considered as an attractive alternative for neurobiologic research.

Animals↗
PubMed1978

Contribution of sodium pump to resting potential of squid giant axon.

The effect of the cardiotonic aglycone, strophanthidin, on sodium and potassium efflux, membrane potential, membrane conductance, potassium permeability, and the shape of the action potential of the giant axon of the squid, Loligo pealei, was examined. Strophanthidin depolarized the membrane to an extent determined by the intracellular sodium concentration, except in axons pretreated with cyanide, in which the effect is abolished. Cyanide itself hyperpolarized the axon membrane. Axons treated with strophanthidin appear to be better potassium electrodes, but this observation is fully accounted for by the stimulating effect of [K]o on an electrogenic sodium pump. The increase in potassium efflux produced by strophanthidin is also well accounted for by the observed membrane depolarization and the known dependence of potassium permeability on membrane potential (e-fold increase in efflux per 6.4 mV depolarization). Strophanthidin has no demonstrable effect on membrane conductance apart from that due to the observed depolarization. These findings support the view that cardiotonic steroids, at least in nerve, are specific inhibitors of the sodium pump, devoid of effects on permeability that might interfere with the study of electrogenic pumping. The alteration in the shape of the action potential after exposure to strophanthidin (deepening of the "underswing") suggests that the strophanthidin-induced membrane depolarization results from the inhibition of a true electrogenic pump, and not from ion redistributions in the vicinity of the membrane.

Action Potentials↗
PubMed1976

Animal studies on bone ingrowth kinetics of ceramic material under dynamic stress.

Two of the primary problems of implants in use today result from the materials used in their construction (metal and polyethylene) and from the necessary additional fixation with bone cement. In order to alleviate these well known difficulties, we studied ceramic material (99.7% Al2O3 with 0.25% MgO) which exhibits several advantages in these areas, but has a diminished bending strength. To take advantage of the ceramic material, we tested a cement-free implantation which should allow unhindered growth of bone tissue to or into the material. In particular, the interface relationship under load bearing was investigated. The course of the tissue differentiation and ingrowth on the surface of the ceramic implants under dynamic stress, was studied by a specifically disegned distance-spacer. These were tested on the femur of foxhounds and sheep, as well as by use of temporary immobilization. Histological investigations in intervals of 4 weeks showed the course of the development of the interface tissue. After removal of the binding materials, the behavior of the implant support is studied in 4-week intervals with free load bearing. Radiological and histological development studies are shown. The results we obtained implicate the use of ceremic impants. But the application in humans still seems to be problematic, as there is a need for designs which are loaded by pressure only.

Aluminum↗
PubMed1975

[The properties required of bioceramics for artificial joints (author's transl)].

Tests of hip joint simulator proove the outstanding friction--and wear-behaviour of high density high purity allumina ceramics, being well known for many years from the field of engineering. According to a comparison of the characteristical physical properties of these special oxide ceramics with the requirements of materials for artificial joints, it is to be expected that wear components being made of high density alumina ceramics will show a very good behaviour in long time runs. This paper will also discuss the problems of body compatability breifly, which have been solved so far already.

Aluminum↗
PubMed1973

Electrogenic sodium pump in squid giant axon.

Squid giant axon possesses a hyperpolarizing electrogenic sodium pump which is stimulated by internal sodium and by external potassium. This conclusion is based on the following observations: strophanthidin depolarizes the membrane and enhances the depolarizing effect of 5 or 10 millimolar external potassium; the magnitude of these effects is directly related to the internal sodium concentration; both effects are abolished by cyanide.

Animals↗
PubMed1970

Voltage clamp of the Aplysia giant neurone: early sodium and calcium currents.

1. The membrane properties of the Aplysia giant neurone were studied under controlled voltage conditions. Emphasis was placed on the early transient currents resulting from step polarizations applied while the ganglion was immersed in different test solutions.2. Early inward-going currents were observed when the neurone was bathed in normal saline (containing both Na and Ca), in Ca-free (Na-containing) saline, in Na-free (Ca-containing) saline, and in the normal saline to which tetrodotoxin 10(-5) g/ml. was added. When both Na and Ca are absent from the bathing solution no evidence for early inward-going current could be found.3. When tetrodotoxin is added to the normal saline, the maximum inward-going current is reduced, and no further reduction of this current is observed when the external Na-concentration is subsequently halved in the presence of the drug. When the external Ca-concentration is increased fivefold in the presence of the drug, the maximum transient current increases significantly.4. Hyperpolarizing prepulses result in a membrane inactivation in the presence of tetrodotoxin or in the absence of Na. In the presence of Na (and absence of tetrodotoxin) no such voltage-dependent inactivation occurs, and for this case, inactivation results only from depolarizing prepulses.

Animals↗
PubMed1968

A ouabain-sensitive membrane conductance.

1. Changes in membrane conductance and potential of sodium-loaded frog muscle fibres were found when the external recovery solution was changed: from cold to warm, to warm plus ouabain, to cold plus ouabain. Comparisons of these measurements for different external solutions were made by leaving the electrodes implanted in the same fibre during all solution changes. (The recovery solutions contained 10 mM-K and 82 mM-Cl.)2. The membrane potential became more negative on warming, less negative when ouabain was added, and still less negative when the ouabain-containing recovery solution was cooled. The membrane conductance increased on warming, increased further on addition of ouabain, and decreased when the ouabain-containing recovery solution was cooled.3. The increase of conductance which occurred on warming decreased with increasing periods in cold recovery. The increase of conductance which occurred on addition of ouabain decreased if the ouabain was added to the recovery solutions of muscles which were more fully recovered.4. The ouabain-sensitivity of the membrane conductance may be dependent upon the sodium-pump rate, or the extent of recovery of the sodium-loaded muscle fibre in the potassium- and chloride-containing recovery solutions.5. It is suggested that if the potassium conductance of the membrane increases with decreasing sodium-pump rates, then during the initial part of the recovery period a non-electrogenic mechanism must be producing a substantial part of the early net potassium influx.

Animals↗
PubMed1968

Sodium and calcium components of action potentials in the Aplysia giant neurone.

1. Action potentials resulting from direct stimulation can be recorded from the soma of the Aplysia giant neurone (located in the visceral ganglion) in sodium-free and in calcium-free external solutions. The neurones were impaled by internal micro-electrodes throughout the change of external solutions.2. Complete replacement of either sodium or calcium in the bathing medium with Tris results in only a partial reduction of spike overshoot. Simultaneous replacement of both sodium and calcium reversibly and quickly abolishes the spike.3. The sodium component of the spike in a calcium-free medium is blocked by tetrodotoxin; the drug has no effect on the calcium-dependent spike in sodium-free medium. Externally applied cobalt chloride blocks only the calcium-dependent component.4. In calcium-free media, the overshoot value varies with sodium concentration in the manner predicted for a sodium electrode. In sodium-free media, the membrane behaves like a calcium electrode.5. These results suggest that, during the normal action potential, both sodium and calcium act as carriers of the inward-directed current.

Action Potentials↗