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Biomedical subjects

R Gruener

Publications and source records attributed to R Gruener.

At least 19 recordsLinked to original sources
PubMed1991

Electrophysiological properties and cholinergic responses in guinea-pig celiac ganglion neurons in primary culture.

Prevertebral neurons enzymatically dissociated from celiac ganglia of adult guinea-pigs were maintained in long-term primary culture. Cells were plated at a density of 95 +/- 15 cm-2, and intracellular electrical activity was measured between 2 and 7 weeks after dissociation. Neurite outgrowth began within 24 h of enzymatic dissociation. Cell survival dropped below 50% after more than two weeks in culture. The resting potential (-53 mV +/- 0.8), time constant (12 ms +/- 1.3), input resistance (47 M omega +/- 8.6), rheobase (0.33 nA +/- 0.02), degree of accommodation, spike amplitude (70 mV +/- 3.0), after hyperpolarization amplitude (-9.5 mV +/- 0.55), and after hyperpolarization duration (88 ms +/- 7.6) in these cells were not different from those recorded from neurons in intact celiac ganglia. A larger proportion (greater than 90%) of cells exhibited fast accommodation (phasic) in response to depolarizing current pulses. Unevoked (spontaneous) depolarizations and action potentials were observed. The cells responded to pressure ejected acetylcholine. Two types of responses consisted of an early rapid depolarization which was attenuated by hexamethonium and a later slow depolarization which was attenuated by atropine. We conclude that prevertebral neurons from guinea-pigs can be maintained in long-term primary culture, that they retain electrophysiological properties similar to intact ganglia and exhibit complex responsivity to acetylcholine.

Acetylcholine↗
PubMed1991

Vector-averaged gravity alters myocyte and neuron properties in cell culture.

To investigate whether changes in the gravitational field of developing neurons and myocytes affect cellular development, we rotated cultures of embryonic spinal neurons and myocytes in a horizontal clinostat. Rotation in the clinostat produces, from the cells' perspective, a "vector-free" gravity environment by continuous averaging of the vector. In this way, rotation in the clinostat simulates the microgravity of space where the gravity vector is substantially reduced. At rotation rates of 1-50 rpm, cellular and nuclear areas of myocytes were significantly enlarged and the number of presumptive nucleoli increased. In neurons, frequent and large swellings appeared along neuritic shafts. Some of these changes were reversible after cessation of rotation. Since our data are generally consistent with findings from other cell types subjected to spaceflight, we suggest that the vector-free gravity environment of the clinostat appears to simulate, at least in part, the microgravity of space. Our data further show that cellular processes are sensitive to altered gravity and suggest that cell development in the microgravity of space may be significantly altered.

Animals↗
PubMed1990

Vector-free gravity disrupts synapse formation in cell culture.

Terrestrial organisms evolved under and are subjected to the constancy of gravity. The organisms having adapted to this environmental factor, it is possible that embryonic development may be modified by exposure to altered gravity. To test the effects of gravity on embryonic development, we monitored the formation of nerve-associated acetylcholine receptor patches (NARPs) as an index of synaptogenesis. Embryonic spinal neuron and myotomal myocyte cocultures were placed in a horizontally rotating clinostat. From the cell's perspective, this results in the cancellation of the gravitational vector because of continuous averaging, thus mimicking the reduced gravitational force encountered in space. NARPs from cultures in which nerve-muscle contact was established before the onset of rotation were unaffected. In contrast, cultures in which nerve contact took place during rotation showed a marked inhibition of NARPs. Moreover, in the myocytes which did exhibit NARPs, the area of the patch was significantly reduced compared with control sister cultures. Several paradigms were used to ascertain that these findings did not result simply from loss of contact between neurites and myocytes, accelerated diffusion of a putative aggregating factor secreted by neurites, or from turbulence in the medium. Our data suggest that the process of synapse formation is sensitive to the gravitational vector. Embryonic development of the nervous system, in space, may therefore be markedly different from that normally occurring on earth.

Animals↗
PubMed1986

Halothane-induced changes in acetylcholine receptor channel kinetics are attenuated by cholesterol.

The single-channel recording technique was used to investigate the role of membrane lipids in the action of general anesthetics on ion channels. We examined the effects of halothane on acetylcholine receptor channels in Xenopus laevis myocytes in which the plasma membrane cholesterol level had been changed by pretreatment with cholesterol-rich or cholesterol-free liposomes. We found that the alteration in acetylcholine receptor channel kinetics, elicited in the presence of clinically-relevant concentrations of halothane, is attenuated when membrane cholesterol is increased and enhanced when membrane cholesterol concentration is decreased. These findings support the idea that general anesthetics interact with synaptic receptor channels indirectly through the lipid domains in which these synaptic proteins are embedded.

Animals↗
PubMed1979

Conduction velocities in single fibers of diseased human muscle.

Focal sarcolemmal lesions, segmental degeneration, and fiber splitting are observed in Duchenne muscular dystrophy and have been proposed to be major contributory causes of dysfunction of this disease. The presence of these abnormalities should affect impulse conduction along the sarcolemma. To test this prediction, we measured conduction velocities of the action potential in normal and diseased human intercostal muscle fibers by means of intracellular microelectrodes. The resting potentials of fibers from patients with Duchenne dystrophy, Becker dystrophy, and motor neuron disease were partially depolarized, and conduction velocities in these fibers were slower than normal. When the membrane potential was artifically hyperpolarized, the conduction velocity in Becker dystrophy fibers was not significantly different from normal. However, conduction velocity values in Duchenne dystrophy or motor neuron disease fibers were significantly lower than normal regardless of the level of membrane hyperpolarization. These data are analyzed in light of the presence of morphologic lesions in the diseased muscle fibers.

Action Potentials↗
PubMed1978

Interpretation of light scattering associated with prolonged neural activity and temperature changes.

Changes in light scattering from lobster giant axon which accompany the action potential were observed during periods of prolonged stimulation and as a function of temperature. At an initial temperature of 10 degrees C most (more than 90%) axons produced positive light scattering signals which increased in amplitude when the temperature was lowered. At 2 and 5 degrees C approximately half of the axons produced positive scattering signals. The remaining half produced negative scattering signals which became positive when the temperature was raised to 10 degrees C. The amplitude of the negative signals followed sigmoid transition to positive values as a function of time. The time and temperature dependence of the signal are interpreted in terms of differential changes between the indices of refraction of the membrane matrix and the open or closed early activation channel.

Action Potentials↗
PubMed1977

Light scattering and excitation in lobster giant axon. Effects of ion substitution.

Changes in the light scattering signal from single giant axons of lobster were observed during the propagation of the action potential in order to correlate membrane excitability with possible structural changes reflected in the optical properties of the axolemma. Substitution of guanidine and aminoguanidine for sodium resulted in a decreased action potential amplitude to 69 and 50% of control values, respectively. The amplitude of the light signal was, however, not significantly changed by these substitutions and is, therefore, reported to be independent of the transmembrane potential and current. The venom of the scorpion Leiurus quinquestriatus caused a marked prolongation of the action potential and the light scattering signal without significantly altering their amplitudes. A two-state model of the early (sodium) activation channel is suggested, in which the light scattering signal is correlated with a possible difference in the scattering efficiency between the states of the channel.

Action Potentials↗
PubMed1976

Muscle insensitivity to tetrodotoxin: induction by alpha-bungarotoxin and removal by submechanical threshold stimulation.

Intramuscular injection of alpha-bungarotoxin (alphaBGT) into rat extensor digitorum longus muscles produced pharmacological blockade of neuromuscular transmission and resulted in denervation-like changes (Berg, D. and Hall, Z. (1975), J. Physiol. (London) 244:659-676). More than 80% of fibers from alphaBGT-injected muscles produced action potentials (ap's) in the presence of tetrodotoxin (TTX, 1 X 10(-6) M). Chronic electrical stimulation of these muscles, below the level necessary to elicit a contraction, resulted in a marked return toward normal of sarcolemmal sensitivity to TTX. After 4 days of submechanical threshold stimulation, less than 45% of alphaBGT-injected fibers produced ap's in the presence of TTX, whereas more than 80% of unstimulated fibers from contralateral control muscles exhibited resistance to TTX. These findings indicate that in addition to sarcolemmal sensitivity to acetylcholine, sensitivity of the sodium conductance mechanism to TTX is also directly influenced by muscle activity independent of contraction.

Animals↗
PubMed1975

Hyperthyroid myopathy. Intracellular electrophysiological measurements in biopsied human intercostal muscle.

Morphological and electrophysiological studies were performed on intercostal muscle biopsies from 2 thyrotoxic patients. The diseased fibers had numerous areas of subsarcolemmal glyogen accumulations and abnormal membranous projections. Both Type I and Type II muscle fibers were atrophied. Diseased fibers were substantially depolarized and when artifically hyperpolarized showed earlier inactivation of the sodium conductance as a function of membrane potential, and a critical depolarization potential more depolarized than in normal fibers. When stimulated at 20 pulses/sec, or faster, the diseased fibers could not generate normal action potentials due to membrane depolarization and the appearance of a marked after-hyperpolarization. Muscle weakness associated with hyperthyroidism is attributed to the reduced membrane excitability.

Adult↗
PubMed1975

Excitability modulation by taurine. Transmembrane measurements of neuromuscular transmission.

The presence of taurine, a non-essential amino acid, in nerve and muscle has been previously associated with inhibition of activity in the central nervous system, with the etiology of epileptogenic foci, and with the muscle weakness of muscular dystrophy. We present here data showing a small and probably insignificant effect of taurine on neuromuscular transmission per se, but significant hyperpolarization of the membrane potential in both taurine-incubated and taurine-loaded muscles. In addition, we found that taurine reduces the time course of the muscle action potential. The results are interpreted in terms of neuromuscular transmission and excitation-contraction coupling consequent to these phenomena. This interpretation is compatable with the hypothesis that taurine is involved in the genesis of muscular dystrophy where the membrane potential is depolarized. Our results and interpretation can also explain the anti-arrhythmic action of taurine on cardiac muscle.

Action Potentials↗
PubMed1975

Intercostal muscle biopsy in human neuromuscular disease. Histochemical and electron microscopic studies.

External intercostal muscle biopsies were examined histochemically and by electron microscopy. The use of this muscle allowed correlation with physiological and pharmacological studies on the same specimens. Changes observed in musclar dystrophy and motor neurone disease resembled those previously described in biopsied limb muscle and underline the particular usefulness of this preparation in the study of human neuromuscular disease.

Adenosine Triphosphatases↗
PubMed1975

Excitability modulation by taurine: action on axon membrane permeabilities.

Taurine, a ubiquitous sulfonic amino acid, has been described as a regulator of membrane activity in both normal and pathologic states of nerve and muscle. The common feature of its effects on brain activity and its interaction with muscle, can be summarized in terms of a stabilizing function on excitable membranes. In this paper, we report data on the ionic mechanisms by which taurine modulates membrane behavior of the lobster giant axon. Our data show that taurine increases membrane permeabilities to potassium and chloride but not to sodium. This increase is transient, showing membrane desensitization during taurine application. A reversal potential for the taurine response was observed at about -85 mV, causing the membrane potential to stabilize near the resting level. In addition, taurine causes a reduction of the action potential duration, resulting primarily from an acceleration of the depolarization phase. These ionic actions of taurine may explain its overall inhibitory effects in the central nervous system and in the retina and may account for its antiarrhythmic properties.

Action Potentials↗
PubMedDate not supplied

Electrophysiologic properties of intercostal muscle fibers in human neuromuscular diseases.

Electrophysiologic properties of biopsied normal and diseased intercostal muscle fibers were examined using intracellular microelectrode techniques. The resting potentials of all diseased muscle fibers were found to be depolarized. Those from Duchenne dystrophy patients showed the largest depolarization, followed by those from patients with myotonic muscular dystrophy, myotonia congenita, and motor neuron disease. All of the diseased fibers except those from myotonia congenita patients demonstrated an imparied ability to generate action potentials. In the latter fibers, the higher-than-normal membrane resistance was associated with hyperexcitability. When the membrane was hyperpolarized to the normal range, however, action potential characteristics in all fibers were near normal, except in motor neuron disease. All action potentials were blocked by tetrodotoxin. These findings--i.e., that all fibers were capable of generating action potentials when hyperpolarized, and that all action potentials were blocked by tetrodotoxin--suggest the relative intactness, in the disease studied here of the regenerative sodium conductance mechanism.

Action Potentials↗