Search PubMed⌕ Search

Biomedical subjects

R Gruener

Publications and source records attributed to R Gruener.

49 records · Page 3Linked to original sources
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↗
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

Effect of external and internal pH changes on K and Cl conductances in the muscle fiber membrane of a giant barnacle.

The membrane potential and conductance of the giant muscle fiber of a barnacle (Balanus nubilus Darwin) were analyzed in relation to changes in the external (3.5-10.0) and the internal (4.7-9.6) pH, under various experimental conditions. A sharp increase in membrane conductance, associated with a large increase in conductance to Cl ions, was observed when the external pH was lowered to values below 5.0. The ratio of Cl to K conductance in normal barnacle saline is between (1/6)-1/7 at pH 7.7, whereas at pH 4.0 the ratio is about 6-9. The behavior of the membrane in response to pH changes in a Cl-depleted muscle fiber shows that the K conductance decreases with decreasing external pH for the whole range of pH examined. A steep increase in Cl conductance is also observed when the internal pH of the fiber is lowered below 5.0. The K to Cl conductance ratio increases with increasing internal pH in a manner very similar to that found when the external pH is raised above 5.0. These facts suggest that the membrane is amphoteric with positive and negative fixed charge groups having dissociation constants such that at pH greater than 5, negative groups predominate and cations permeate more easily than anions, while at lower pH positive groups predominate, facilitating the passage of anions through the membrane.

Biological Transport, Active↗
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↗