Biomedical subjects

C E Morris

Publications and source records attributed to C E Morris.

69 records · Page 4Linked to original sources

PubMed1986

Multiple conductance states of the acetylcholine receptor channel complex.

The acetylcholine-activated channel of vertebrate skeletal muscle, as manifested in cultured, developing cells, is able to adopt more than one conductance state. This paper briefly reviews the evidence for such multiple conductance channels and presents results showing that the amplitude of subconductance states does not depend on agonist size and (or) valence. This seems to rule out the possibility that subconductances occur during partial occlusion of the channel (by agonist molecules) and supports the idea that subconductances represent discrete, allosterically activated channel conformations.

Animals↗

PubMed1984

Central nervous system features of a nicotine-resistant insect, the tobacco hornworm Manduca sexta.

The purpose of this study is to look for structural correlates of the demonstrated nicotine-insensitivity of larval Manduca sexta CNS, an insensitivity which is only slightly perturbed by desheathing (a technique used to disrupt perineurial diffusion barriers). The general organization of the hornworm ganglion is found to conform to the conventional insect pattern, but the following points are noted and discussed in terms of their potential relationship to nicotine-insensitivity: the damage caused to perineurial cells by desheathing is extremely localized, with cells immediately adjacent to the torn region showing good ultrastructural integrity; ionic lanthanum does not gain access to the subperineurial extracellular space following desheathing; lanthanum penetrates the ganglion in the cytoplasm of tracheal cells damaged peripherally during desheathing, but is excluded from the extracellular space surrounding such tracheal cells; smooth endoplasmic reticulum is much in evidence in perineurial cells and tracheal cells, sites where it might be implicated in nicotine detoxification; individual basal perineurial cells appear to cover extensive regions of the ganglion, thereby limiting intercellular diffusion.

Animals↗

PubMed1983

Successive openings of the same acetylcholine receptor channel are correlated in open time.

Previous analysis of single-channel current records has shown that both the opening and closing transitions of chemically activated ion channels are operated by fast and slow kinetic processes. The fast component in the kinetics of channel opening has been interpreted as the reopening of a channel that has just closed. The fast component in the kinetics of channel closure has many possible explanations and is therefore more difficult to interpret. We can gain insight into the closing process by asking whether the lifetimes of successive openings of an acetylcholine receptor channel are correlated in open-state lifetime. Five kinetic models of channel closure are considered. Two of these models predict uncorrelated open-state lifetimes, one predicts correlated open-state lifetimes, and for two others a range of behavior is possible. Acetylcholine receptor channel data from cultured rat muscle are analyzed to show that open-state lifetimes are correlated, eliminating two models of channel gating.

Acetylcholine↗

PubMed1983

Single-channel currents activated by curare in cultured embryonic rat muscle.

Single cholinergic receptor channel currents activated by curare were recorded in tissue-cultured embryonic rat muscle, directly confirming curare's action as a weak cholinergic agonist. In embryonic muscle, curare, in addition to its classical action as a competitive cholinergic antagonist, produces small sustained depolarizations which can be blocked by alpha-bungarotoxin. The single-channel events are of short duration but otherwise exhibit the major features observed with other cholinergic agonists. The single-channel events are blocked by alpha-bungarotoxin. Two values of unit conductance, 30.4 +/- 3.5 pS and 47 +/- 6 pS, were measured in cells from different cultures. Histograms of open-state duration are well fit by a distribution which is a sum of two exponentials, with time constants of 0.33 +/- 0.08 msec for the fast component and 1.84 +/- 0.43 msec for the slow component.

Action Potentials↗

PubMed1981

Revised transcription map of the late region of bacteriophage T7 DNA.

The genes in the late region of the bacteriophage T7 genome are transcribed by a phage-specified RNA polymerase in two temporal classes (II and III). Through the use of an agarose-formaldehyde gel system that permits the resolution of high-molecular-weight RNAs, transcription of template DNA that had been cut with various restriction endonucleases, and transcription of isolated restriction fragments from the class II region, six previously unreported promoters utilized by the phage RNA polymerase in vitro have been mapped between 28 and 46% of the T7 genome. No evidence could be found for the existence of a promoter at 61% that had previously been reported to give rise to a diffuse band (species I RNA) in acrylamide-agarose gels.

Chromosome Mapping↗

PubMed1976