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G D Fischbach

Publications and source records attributed to G D Fischbach.

At least 91 records · Page 5Linked to original sources
PubMed1978

A transition temperature for acetylcholine channel conductance in chick myoballs.

1. The temperature dependence of ACh channel conductance (gamma) and channel open time (tau) was determined by analysing ACh induced membrane current fluctuations in voltage clamped chick myoballs. 2. gamma decreased from 25-30 pmho at 37 degrees C to less than 5 phmo at 10 degrees C. An Arrhenius plot of gamma vs. temperature exhibited a clear break or 'transition temperature' at 20 degrees C. 3. tau increased from 2 msec at 37 degrees C to 16 msec at 10 degrees C. The Arrhenius plot of tau vs. temperature was linear. No transition temperature was detected. 4. Submicellar concentrations of the non-ionic detergent, Triton X-100 reversibly blocked ACh respnses. The effect was all-or-none at the molecular level. 5. These results are consistent with the possibility that the fluidity of membrane lipids in the ACh receptor micro-environment may influence the degree to which the channel can open.

Acetylcholine↗
PubMed1978

Accumulation of acetylcholine receptors and acetylcholinesterase at newly formed nerve-muscle synapses.

Nerve-muscle synapses form and the postsynaptic membrane begins to differentiate rapidly in vitro. New clusters of AChRs have been located at transmitting synapses within 3 hours after a competent neurite contacted a receptive myotube. Receptors within new subneural clusters are not identical with receptors at adult end-plates: they are metabolized rapidly and their mean channel open time is prolonged. In this sense synapse formation must be considered a drawn out affair. AChE also accumulates at synapses soon after functional contacts are established. The cleft enzyme is apparently regulated differently than receptors in the postsynaptic membrane. Muscle activity is necessary for the early accumulation of AChE, but not for the clustering of receptors. Further studies in vitro should be useful for analysis of the role of muscle activity, of the local neural influence on the postsynaptic membrane, and of the mechanism of the muscle response.

Acetylcholine↗
PubMed1977

The action potential of chick dorsal root ganglion neurones maintained in cell culture.

1. The directly evoked action potential of dissociated, embryonic, chick, dorsal root ganglion (DRG) neurones maintained in cell culture is prolonged compared to spinal cord cell spikes and the re-polarization phase is marked by a plateau. 2. Evidence was obtained that both Ca2+ and Na+ carry inward current across the active soma membrane. Ca2+ because: overshooting spikes persist in tetrodotoxin (TTX) or Na+-free media; in the presence of TTX (or absence of Na+) spike size varies directly with extracellular Ca2+ and spikes are eliminated by Co2+. Na+ because: spikes persist in the presence of Co2+ or Ca2+-free media; in the presence of Co2+ (or absence of Ca2+) spike varies directly with extracellular Na+ and spikes are blocked by TTX. 3. On the other hand, Ca2+ plays less if any role in action potentials conducted along sensory nerve cell processes. Conducted spikes could not be evoked in TTX containing or Na+-free media. 4. A long-lasting depolarization follows the action potential in some neurones. This depolarization is associated with an increase in membrane conductance and appears to drive the membrane potential to ca. -30mV. It persists when conducted impulses are blocked so it is probably not a recurrent synaptic potential. 5. It is suggested that combined Ca2+-Na+ spikes observed in isolated sensory neurones in vitro reflect the action potential of adult sensory cells but the possibility that they represent an early stage in development is also discussed.

Action Potentials↗
PubMed1973

Regulation of muscle acetylcholine sensitivity by muscle activity in cell culture.

Muscle in tissue culture provides a good system for studying longterm changes in surface membrane acetylcholine sensitivity. Muscle fibers stimulated intermittently over prolonged periods are less sensitive to iontophoretically applied acetylcholine and bind less (125)I-labeled alpha-bungarotoxin than inactive fibers.

Acetylcholine↗