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Rapid membrane repair in two transected giant axons
by Krause, Todd Lawrence, Ph.D., The University of Texas at Austin, 1993, 209 pages; AAT 9323456
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Advisor: Bittner, George D.
School: The University of Texas at Austin
School Location: United States -- Texas
Index terms(keywords): Loligo pealei, Sepioteuthis lessoniana, Lumbricus terrestris
Source: DAI-B 54/04, p. 1822, Oct 1993
Source type: DISSERTATION
Subjects: Neurology, Cellular biology, Anatomy & physiology, Animals
Publication Number: AAT 9323456
Document URL: Shibboleth Authentication Request
ProQuest document ID: 747462731
Abstract (Document Summary)
For a nerve cell to survive transection, toxic changes in intracellular concentrations of ions or macromolecules must be prevented by the formation of a barrier (seal) at the site of damage. Despite the importance of sealing to the survival of damaged neurons and other cell types, sealing has not been well characterized and its mechanism is unknown in any cell type.
Using several functional (membrane potential, input resistance, complex input-impedance, and injury current density) and morphological (phase contrast microscopy, video-enhanced differential interference contrast microscopy, light microscopy and electron microscopy) measures, I assessed sealing in two invertebrate giant axons--the giant axon of squid (Loligo pealei and Sepioteuthis lessoniana) and the medial giant axon of earthworm (Lumbricus terrestris). The functional and morphological data together strongly suggest that when transected in standard salines, the squid axon does not seal within 2.5 hr, whereas the earthworm axon seals within 1 hr. Neither axon seals within 2.5 hr when transected in divalent cation free saline. Further, my data do not support the conventional notion that sealing occurs by constriction and fusion of axolemmal membranes at the cut end. Rather, my data indicates that earthworm axon seals by forming a plug of large $(\ge$5 $\mu$m) injury-induced vesicles at the cut axonal end.
I also assessed the ability of naturally occurring mechanisms of seal formation to facilitate the reconnection of lesioned axons by artificial means (i.e. polyethylene glycol). When the natural ability of earthworm axon to seal-off its cut end was controlled by adjusting the ionic concentration of the bath saline, lesioned axons were efficiently reconnected using polyethylene glycol. The extent of axonal reconnection was extensively characterized using morphological (light microscopy, electron microscopy, passive diffusion of intraxonally injected dye across the reconnection site) and functional (membrane potential, action potential and electrotonic potential conduction through the reconnection site) measures.
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Functional characterization of Electrophorus electrocyte sodium channels
by Shenkel, Scott, Ph.D., Yale University, 1992, 147 pages; AAT 9235556
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Advisor: Sigworth, Frederick J.
School: Yale University
School Location: United States -- Connecticut
Index terms(keywords): Electrophorus electricus
Source: DAI-B 53/07, p. 3350, Jan 1993
Source type: DISSERTATION
Subjects: Anatomy & physiology, Animals, Neurology, Biophysics
Publication Number: AAT 9235556
Document URL: Shibboleth Authentication Request
ProQuest document ID: 744439081
Abstract (Document Summary)
The first voltage gated Na channel to be purified biochemically and to be cloned and sequenced is that present in the electrocytes of the electric organ of the electric eel Electrophorus electricus. To complement what is known about its structure my work has focused on the study of the functional properties of the electrocyte Na channel based on electrophysiological measurements of purified, modified reconstituted channels in planar lipid bilayers and unmodified channels in patches of intact electrocyte membrane.
Na channels modified by mild trypsin-treatment and then incorporated into planar lipid bilayers have properties of steady-state voltage-dependence of activation, single-channel conductance, and sensitivity to tetrodotoxin and saxitoxin similar to those of unmodified Na channels in nerve and muscle cell membranes. One exception is the unusually high P$\sb{\rm Na}$/P$\sb{\rm K}$ selectivity ratio of 41, which is two to four times the values previously reported for Na channels in nerve and muscle cells.
My patch-clamp experiments on intact electrocytes have shown that the high P$\sb{\rm Na}$/P$\sb{\rm K}$ observed in the trypsinized channels in bilayers is a real property of the channels in the intact cell membrane. In addition, the trypsinized channels in bilayers and native channels have similar properties of steady-state voltage-dependence of activation and single-channel conductance. Furthermore, the properties of activation, inactivation and single-channel conductance of the electrocyte Na channel are similar to those of Na channels in nerve and muscle cell membranes. A surprising finding is the large variation in P$\sb{\rm Na}$/P$\sb{\rm K}$ among patches from the electrocytes observed under identical recording conditions. My results support the conclusion that there is heterogeneity in the selectivty properties of the Na channels.
The high Na channel density in the intact electrocyte has allowed the recording of gating currents in isolated membrane patches. The properties of these gating currents were found to be similar to those of the squid giant axon and other preparations.
by Krause, Todd Lawrence, Ph.D., The University of Texas at Austin, 1993, 209 pages; AAT 9323456
» More Like This - Find similar documents
Advisor: Bittner, George D.
School: The University of Texas at Austin
School Location: United States -- Texas
Index terms(keywords): Loligo pealei, Sepioteuthis lessoniana, Lumbricus terrestris
Source: DAI-B 54/04, p. 1822, Oct 1993
Source type: DISSERTATION
Subjects: Neurology, Cellular biology, Anatomy & physiology, Animals
Publication Number: AAT 9323456
Document URL: Shibboleth Authentication Request
ProQuest document ID: 747462731
Abstract (Document Summary)
For a nerve cell to survive transection, toxic changes in intracellular concentrations of ions or macromolecules must be prevented by the formation of a barrier (seal) at the site of damage. Despite the importance of sealing to the survival of damaged neurons and other cell types, sealing has not been well characterized and its mechanism is unknown in any cell type.
Using several functional (membrane potential, input resistance, complex input-impedance, and injury current density) and morphological (phase contrast microscopy, video-enhanced differential interference contrast microscopy, light microscopy and electron microscopy) measures, I assessed sealing in two invertebrate giant axons--the giant axon of squid (Loligo pealei and Sepioteuthis lessoniana) and the medial giant axon of earthworm (Lumbricus terrestris). The functional and morphological data together strongly suggest that when transected in standard salines, the squid axon does not seal within 2.5 hr, whereas the earthworm axon seals within 1 hr. Neither axon seals within 2.5 hr when transected in divalent cation free saline. Further, my data do not support the conventional notion that sealing occurs by constriction and fusion of axolemmal membranes at the cut end. Rather, my data indicates that earthworm axon seals by forming a plug of large $(\ge$5 $\mu$m) injury-induced vesicles at the cut axonal end.
I also assessed the ability of naturally occurring mechanisms of seal formation to facilitate the reconnection of lesioned axons by artificial means (i.e. polyethylene glycol). When the natural ability of earthworm axon to seal-off its cut end was controlled by adjusting the ionic concentration of the bath saline, lesioned axons were efficiently reconnected using polyethylene glycol. The extent of axonal reconnection was extensively characterized using morphological (light microscopy, electron microscopy, passive diffusion of intraxonally injected dye across the reconnection site) and functional (membrane potential, action potential and electrotonic potential conduction through the reconnection site) measures.
........................
Functional characterization of Electrophorus electrocyte sodium channels
by Shenkel, Scott, Ph.D., Yale University, 1992, 147 pages; AAT 9235556
» More Like This - Find similar documents
Advisor: Sigworth, Frederick J.
School: Yale University
School Location: United States -- Connecticut
Index terms(keywords): Electrophorus electricus
Source: DAI-B 53/07, p. 3350, Jan 1993
Source type: DISSERTATION
Subjects: Anatomy & physiology, Animals, Neurology, Biophysics
Publication Number: AAT 9235556
Document URL: Shibboleth Authentication Request
ProQuest document ID: 744439081
Abstract (Document Summary)
The first voltage gated Na channel to be purified biochemically and to be cloned and sequenced is that present in the electrocytes of the electric organ of the electric eel Electrophorus electricus. To complement what is known about its structure my work has focused on the study of the functional properties of the electrocyte Na channel based on electrophysiological measurements of purified, modified reconstituted channels in planar lipid bilayers and unmodified channels in patches of intact electrocyte membrane.
Na channels modified by mild trypsin-treatment and then incorporated into planar lipid bilayers have properties of steady-state voltage-dependence of activation, single-channel conductance, and sensitivity to tetrodotoxin and saxitoxin similar to those of unmodified Na channels in nerve and muscle cell membranes. One exception is the unusually high P$\sb{\rm Na}$/P$\sb{\rm K}$ selectivity ratio of 41, which is two to four times the values previously reported for Na channels in nerve and muscle cells.
My patch-clamp experiments on intact electrocytes have shown that the high P$\sb{\rm Na}$/P$\sb{\rm K}$ observed in the trypsinized channels in bilayers is a real property of the channels in the intact cell membrane. In addition, the trypsinized channels in bilayers and native channels have similar properties of steady-state voltage-dependence of activation and single-channel conductance. Furthermore, the properties of activation, inactivation and single-channel conductance of the electrocyte Na channel are similar to those of Na channels in nerve and muscle cell membranes. A surprising finding is the large variation in P$\sb{\rm Na}$/P$\sb{\rm K}$ among patches from the electrocytes observed under identical recording conditions. My results support the conclusion that there is heterogeneity in the selectivty properties of the Na channels.
The high Na channel density in the intact electrocyte has allowed the recording of gating currents in isolated membrane patches. The properties of these gating currents were found to be similar to those of the squid giant axon and other preparations.