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Biomedical subjects

W Finger

Publications and source records attributed to W Finger.

At least 55 records · Page 3Linked to original sources
PubMed1983

Excitatory postsynaptic channels operated by quisqualate in crayfish muscle.

Small crayfish muscle fibers were voltage clamped and membrane current noise elicited by bath application of quisqualate, a compound structurally related to the excitatory transmitter glutamate, was measured. It was found that quisqualate activates the same excitatory postsynaptic receptors as glutamate but its affinity for these receptors is about one hundred times larger. Noise analysis revealed that the high potency of quisqualate was attributable in part to an increased apparent mean channel open time, tau noise (quisqualate), which was about ten times larger than on activation by glutamate. The channel conductance gamma(quisqualate), however, was about three times smaller than gamma(glutamate). At T = 8 C and E = -60 mV, tau noise (quisqualate) = 9.3 +/- 1.8 ms and gamma(quisqualate) = 9.7 +/- 1.1 pS resulted. tau noise (quisqualate) decreased with hyperpolarization but it was much less voltage dependent than tau noise (glutamate): tau noise (quisqualate) = 6.0 ms . exp (E/362 mV). Both gamma(quisqualate) and alpha = tau noise (quisqualate) increased with temperature (Q10 approximately 1.6). This temperature dependence was characterized by the temperature independent activation energies E gamma = 29.1 +/- 1.7 kJ/mol and E alpha = 33.9 +/- 1.3 kJ/mol. Concanavalin A which blocks desensitization of the quisqualate/glutamate receptors did not influence tau noise (quisqualate) significantly.

Animals↗
PubMed1983

Glutamate activated postsynaptic channels in crayfish muscle investigated by noise analysis.

Excitatory synaptic channels in crayfish muscle were investigated under various experimental conditions. Small muscle fibres of length l less than or equal to 0.6 mm were voltage clamped, spatial control of the voltage being sufficient up to at least 500 Hz. Excitatory synaptic current was induced by superfusion of glutamate. The power density spectra of this current could be fitted by single component Lorentz curves. The analysis revealed a mean open time tau noise = 0.93 ms and a conductance gamma = 32.3 pS of the glutamate operated ion channels (membrane potential E = -60 mV, temperature T = 8 degrees C). Both the conductance gamma and the channel closing rate alpha = tau -1 noise increased significantly with temperature (Q10 approximately 2). The temperature dependence of gamma and alpha could be described by Arrhenius equations with the temperature independent activation energies E gamma = 42.3 kJ/mol and E alpha = 50.2 kJ/mol. alpha also dependent on the membrane potential, increasing about e-fold when the membrane was hyperpolarized by 120 mV. The potential dependence varied considerably from fibre to fibre. The mean channel open time tau noise agreed with the time constant of decay tau (sEPSC) of spontaneous excitatory postsynaptic currents (sEPSCs).

Animals↗
PubMed1983

Effects of concanavalin A on glutamate operated postsynaptic channels in crayfish muscle.

Small crayfish muscle fibres were voltage clamped, and synaptic current noise induced by bath application of glutamate was measured. Desensitization of the glutamate receptors was blocked by preincubating the fibres with 0.3-1.0 mumol/l concanavalin A (Con A) for at least 30 min. The power density spectra of the glutamate current noise could be fitted by single component Lorentz curves. The lectin Con A did not influence significantly the conductance gamma of the glutamate channels but increased their mean open time, tau noise. The respective mean values found at T = 8 degrees C and E = -60 mV were gamma = 23.5 +/- 7.0 pS and tau noise = 1.5 +/- 0.2 ms. Both the conductance gamma and the closing rate alpha = tau -1 noise increased with temperature (Q10 approximately 1.9). This temperature dependence was characterized by the activation energies E gamma = 35.2 +/- 7.1 kJ/mol and E alpha = 46.9 +/- 2.1 kJ/mol. The potential dependence of tau noise was almost completely abolished by Con A.

Animals↗
PubMed1983

A comparison of enzyme immunoassay and bioassay for the quantitative determination of antibodies to tetanus toxin.

Antibodies to tetanus toxin were induced in sheep by hyperimmunization over 24 weeks. Bleeds taken at weeks 4, 8, 20 and 30 were assayed for antibody titre by both an enzyme immunoassay (EIA) using a newly-described urease enzyme/substrate system and by bioassay in mice. There was a very good correlation between the two assay systems and, with the exception of the week 4 Bleeds, the relationship was the same at all stages of hyperimmunization regardless of titre, adjuvant, or whether toxin or toxoid was used as immunogen or for coating the plates. The results establish that the EIA can replace the bioassay for the determination of tetanus antitoxin in ovine sera.

Animals↗
PubMed1983

Accuracy of stone-casts produced from selected addition-type silicone impressions.

The present study has shown that there is no correlation between the free curing contraction of three selected addition-type silicone impression materials and the effective contraction determined as the accuracy of stone dies produced in dental impressions of these materials. Depending on specific rheologic properties, the free curing contraction of an impression material can be partly compensated for by flow.

Calcium Sulfate↗
PubMed1983

Evaluation of glass ionomer luting cements.

In the present study the three glass ionomer luting cements available on the Scandinavian market in June, 1982 were evaluated by comparison with a zinc phosphate and a zinc carboxylate cement. The following properties were tested: effective maximum grain size, retention, strength, bond strength to dentin, disintegration in and absorption of water and solubility in 0.001 n lactic acid. The glass ionomer cements proved to be fully acceptable luting materials.

Absorption↗
PubMed1982

Enhanced release of inhibitory and excitatory transmitter quanta in the crayfish neuromuscular junction by glycine and GABA.

High concentrations of glycine (greater than or equal to 0.1 mol/l) applied to the bathing medium of voltage-clamped muscle fibres elicited high rates of spontaneous inhibitory miniature currents (sIPSCs) which were identified by means of the noise analysis technique. The rate of spontaneous excitatory miniature currents (sEPSCs) was not raised appreciably in presence of these high concentrations of glycine. Contrary to the effect of glycine, high concentrations of GABA (greater than or equal to 0.1 mol/l) desensitized inhibitory postsynaptic receptors and induced high rates of sEPSCs. When, in addition to GABA, glycine was also applied at high concentrations, the discharge of sEPSCs was suppressed. Moreover, glycine reduced significantly the current noise intensity elicited by activation of excitatory postsynaptic membrane channels with 1.10(-4) mol/l glutamate. The experiments suggest an inhibitory action of glycine on the excitatory receptor--channel complex in the postsynaptic membrane.

Animals↗
PubMed1982

A modified phosphate-bonded casting investment.

An experimental phosphate-bonded casting investment with negligible setting expansion and a thermal expansion of 1.6%, sufficient to compensate for the solid thermal shrinkage of conventional dental gold alloys and high-precious alloys for the porcelain fused to metal technique, is described. When used in a ringless casting technique the investment makes it possible to produce cast restorations with a consistent slidefit. In combination with a die spacer technique the new investment make if possible routinely to produce cast restorations with a consistent and known degree of loosefit.

Chemical Phenomena↗
PubMed1982

Effect of casting methods on accuracy of peridental restorations.

The present study has shown that the accuracy of peridental gold alloy castings depends 1) on the type of casting machine used, 2) on the diameter of the casting sprue, and 3) on the strength properties of the investment material. The dependence between the accuracy and the three factors mentioned is based on erosion of the investment mold by the inflow of the liquid casting alloy. The vacuum casting technique proved to be a more gentle casting method than centrifugal and vacuum/pressure techniques.

Chemical Phenomena↗
PubMed1981

Analysis of miniature spontaneous inhibitory postsynaptic currents (sIPSCs) from current noise in crayfish opener muscle.

Deviating from the normal situation, some crayfish muscle fibres showed spontaneous inhibitory activity: discharge of large inhibitory postsynaptic currents, IPSCs, alternating with long lasting bursts of current noise. Analysis of the bursts of current noise revealed that they are composed of spontaneous miniature unit currents, sIPSCs. In the burst periods the sIPSCs occurred with an average rate of 3.5--10 k Hz and had an amplitude of about alpha = 90 pA at a driving force delta E = 10 mV. The peak conductance gamma alpha = alpha/delta E of the sIPSCs was gamma alpha = 9.2 nS +/- 0.5 (S.D., n = 5) for membrane potentials between E = --60 mV and E = --80 mV. gamma alpha seemed to decrease when the membrane was hyperpolarized. The time constants of decay, tau of the sIPSCs were identical with tau of the IPSCs. Further, tau and its potential dependence agreed with the mean lifetimes of inhibitory postsynaptic channels operated by gamma-aminobutyric acid (GABA) [Dudel et al. 1977, 1980]. Synchronized opening of about 750 inhibitory synaptic channels generates a sIPSC. Analysis of this anomalous bursting inhibitory activity thus yields the size of the inhibitory quantum of transmission, which could not be obtained from IPSCs.

Animals↗
PubMed1980

Efficacy of the two-microelectrode voltage clamp technique in crayfish muscle.

Crayfish muscle fibres of different dimensions were voltage clamped and white noise current was injected into the fibres at various distances from the voltage clamp current electrode. The clamp current was measured and power spectral densities were calculated. This method revealed the efficacy of the voltage clamp in these fibres. In large fibres (l = 1.8-2.0 mm; diameter = 100-180 micrometer) a space clamp was achieved only for a band width delta f = 40 Hz. At a distance of 100 micrometer from the clamp electrodes delta f was 250-500 Hz. In fibres of medium size (l = 1.0-1.3 mm; diameter = 60-120 micrometer) delta f was about 80 Hz and about 800 Hz at a distance of 100 micrometer. In experiments with very small muscle fibres (l = 400-600 micrometer; diameter = 30-50 micrometer) delta f was more than 500 Hz. The improvement of the space clamp for the smaller muscle fibres resulted mainly from the reduced total membrane capacity, cm, of these fibres. The limitations of the space clamp could be derived from the impedance properties of the fibres. The band width of the space clamp correlated with the band width for which the square of the absolute impedance, /Zp/2, of the muscle fibre could be described by a simple RC-model. This correlation was demonstrated in a model circuit. Power density spectra of membrane current fluctuations were measured also. To optimize the resolution of these measurements the contribution of instrumental noise was minimized. The effects of instrumental noise are discussed.

Animals↗
PubMed1980

Inhibitory synaptic channels activated by gamma-aminobutyric acid (GABA) in crayfish muscle.

Small crayfish muscle fibres were voltage clamped and synaptic current elicited by superfused GABA solutions was measured. Analysis of the fluctuations of synaptic current and of relaxations of the current after voltage steps yielded analogous results. The current has two components. The first component is characterized by the opening of synaptic channels with a single channel conductance gamma = 9 pS and an average open time tau = 5 ms, measured at 23 degrees C and - 100 mV. tau depends on the membrane potential, tau E = tau 0 x eE/epsilon, and epsilon was about +100 mV in the average. The channel open time agrees with the time constant of decay of the inhibitory postsynaptic current (IPSC) elicited by a nerve stimulus. The current is carried by chloride ions. The second current component is much slower, the average channel open time was tau s = 33 ms at 23 degrees C and -60 mV. The open time tau s of the slow component also was shortened on hyperpolarization. The reversal potential for the current component was more positive than -50 mV. This slow component also seems to be a synaptic one.

Animals↗
PubMed1980

Closing of membrane channels effected by gamma-amino-butyric acid (GABA) in crayfish muscle.

In a small crayfish muscle fibers current elicited by superfusion of GABA was studied. In the majority of the fibers the GABA induced synaptic current relaxed after voltage steps in agreement with the known voltage and time dependence of the inhibitory chloride channels. In about 20% of the preparations, however, at low GABA concentrations of 5-50 mumol/l an anomalous i--response occurs, namely a reduced total membrane conductance in response to GABA. This i--response can be described by a closing of membrane channels, in which the average closed time increases on hyperpolarization. Equivalent conductance reductions are also observed in measurements of the power spectral density of the current noise. In addition to the noise spectrum of the inhibitory chloride current (Dudel et al. 1980), a spectrum with a higher value of the corner frequency appeared, which seems to represent the i- component. In contrast to the inhibitory chloride current, the i--response is not blocked by picrotoxin. The receptors and channels which mediate the i--response thus seem to be different from those of the inhibitory iCl. Several lines of evidence indicate that the i--response is due to the closing of potassium channels. The i--response counteracts the inhibitory effect of GABA at low GABA concentrations and can distort the dose-response curve.

Animals↗
PubMed1980

Strength properties of some gypsum-bonded casting investments.

The present investigations show that there is no correlation between on the one hand the wet and the dry compressive strength of the three gypsum-bonded investments studied and on the other the compressive strength of the investments at burn-out temperature. The study also demonstrated that there is no correlation between the compressive strength and the fracture resistance of sharp edges of the investment mold when exposed to the impact of the casting alloy entering the mold. The inconveniences caused by the fracture of such edges are prevented by a moderate rounding of the corresponding parts in the preparation.

Calcium Sulfate↗
PubMed1980

Effect of the setting expansion of dental stone upon the die precision.

The present investigation has shown that the setting expansion of two dental stones when measured according to the ADA Specification No. 25, was lower than the expansion determined by a dial gauge method. The values from this latter test and the percentage deviation of the diameter of full crown stone dies (produced in individual silicone impressions) from the base diameter of the original preparation were identical. A reduction of the effective expansion to a value of 0.05% or less is desirable and proved possible for the stone materials studied without altering other important properties.

Calcium Sulfate↗
PubMed1980

Surface roughness of gold alloy castings.

The present investigation has shown that the surface of gold alloys cast in both a new and probably improved investment and in two commercial gypsum-bonded investments fulfills all conventional clinical requirements as regards retention and precision of the cemented restorations and easy polishability. With a view to retention the sometimes slightly rougher surfaces of castings in the new investment are advantageous.

Dental Casting Investment↗
PubMed1980

An improved dental casting investment.

In the present investigation a gypsum-bonded investment is presented with negligible setting expansion and a thermal expansion of 1.7%. This investment can and should be used without a steel casting ring. In combination with an earlier described die-spacing technique the new investment facilitates the production of gold inlays and crowns which, independent of type, will show a suitable degree of loose-fit in or on the preparations in the patient's mouth.

Calcium Sulfate↗