Search PubMed⌕ Search

Biomedical subjects

R Epstein

Publications and source records attributed to R Epstein.

At least 145 records · Page 8Linked to original sources
PubMed1970

Desensitization of gamma aminobutyric acid (GABA) receptors in muscle fibers of the crab Cancer borealis.

Carcinus muscle fibers respond to gamma-aminobutyric acid (GABA) with a conductance increase that subsides rather rapidly. In the larger fibers which have low input resistance the decrease may disappear within 2 min. The inhibition of the excitatory postsynaptic potentials (EPSP's) by GABA nevertheless persists as long as the drug is applied. The subsidence of the increased conductance indicates that the membrane of the inhibitory synapses has become desensitized to GABA. The persistence of inhibition of the EPSP's appears to be due to an action of the drug on the presynaptic terminals of the excitatory axons which reduces or blocks the secretory activity that releases the excitatory transmitter.

Aminobutyrates↗
PubMed1970

Heterosynaptic facilitation and post-tetanic potentiation in Aplysia nervous system.

1. Heterosynaptic facilitation was defined as an increase of amplitude of a test excitatory post-synaptic potential (EPSP) after the activation of a pathway (heterosynaptic pathway) different from that which produced the test EPSP. This phenomenon has been studied in Aplysia central nervous system under conditions which excluded the participation of post-tetanic potentiation.2. A unitary test was produced in the left and right giant cells, by indirect stimulation of an interneurone located in the peri-oesophageal ring.3. During heterosynaptic stimulation, orthodromic and antidromic activation of the test interneurone was prevented by (1) isolating the synaptic afferent region of the test interneurone from the tested synapse on the right giant cell by a sucrose block applied on the left pleurovisceral connective, and (2) using physiological stimulation of a piece of skin as a heterosynaptic stimulus. Under these conditions which prevented any firing in the test interneurone, heterosynaptic facilitation is observed as a 200% increase of amplitude of the test EPSP in the right cell which lasted more than 15 min. When instead of the physiological stimulus a supramaximal electrical stimulation of the nerves afferent to the abdominal ganglion was used, the increase of amplitude of the test EPSP could reach as much as 500% of its original amplitude. The effectiveness of such heterosynaptic stimulus was smaller when it was applied in the absence of a block of the left pleuro-visceral connective.4. It was possible to produce heterosynaptic facilitation when the preparation was cooled to 7-9 degrees C or if Li(+) replaced Na(+) in the medium. Both of these changes suppressed post-tetanic potentiation.5. It was concluded that heterosynaptic facilitation is a phenomenon different from post-tetanic potentiation. Heterosynaptic facilitation is similar to heterosynaptic inhibition seen in other cells in the same preparation, except for the polarity of action. Both phenomena seem to result from comparable mechanisms, probably acting on the quantity of transmitter released.

Action Potentials↗
PubMed1968

Relationship between protein and ribonucleic acid synthesis during outgrowth of spores of Bacillus cereus.

The rate of protein and ribonucleic acid (RNA) synthesis was examined during the outgrowth of spores of Bacillus cereus T in a chemically defined medium. RNA synthesis started 2.5 min after the initiation of germination, and protein synthesis after 4 min. Addition of a complete amino acid supplement and uracil supported high rates of RNA and protein synthesis throughout outgrowth. To determine the relationship between the rate of protein (k) and RNA synthesis, the kinetics of formation of various classes of RNA were followed during outgrowth. Ribosomal RNA (rRNA) comprised a relatively constant fraction of the total RNA throughout outgrowth (71 to 78%). The classes of RNA synthesized during this period were determined by germinating spores in radioactive uracil and then at intervals following their stability to actinomycin D. Initially, labile RNA comprised the largest fraction of newly formed RNA (DeltaRNA), and this proportion decreased during outgrowth. The ratio of k/rRNA or k/Delta stable RNA varied considerably during outgrowth, whereas the ratio of k/labile RNA remained constant. The data suggest that the rate of protein synthesis is not rigidly coupled to either total or newly synthesized rRNA (ribosomes) during the early stages of outgrowth.

Amino Acids↗