The role of axon-glial cell interactions in perineural potassium homeostasis of the giant axon of the crayfish, Procambarus clarkii / by Sami Hassan.
| Author/creator | Hassan, Sami author. |
| Other author | Kalmus, Gerhard W., degree supervisor. |
| Other author | East Carolina University. Department of Biology. |
| Format | Theses and dissertations |
| Production | 1988. |
| Description | [v], 115 leaves : illustrations ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | The electrical resistance in series with the axon membrane (Rs) is generally modeled as the intercellular pathway for current flow through the perineural glial (Schwann cell) sheath. The Rs of the medial giant axon of the crayfish, Procambarus clarkii, was found to vary with conditions known to affect the electrical properties of the perineural glia. The effect of anisosmotic media and different K+o concentrations on the Rs were also studied to determine if the changes in Rs correlated with glial cell volume regulatory responses and potassium uptake. Rs was estimated from computer analyzed voltage waveforms generated by axial wire-constant current and space clamp techniques. The average Rs for all axons was 6.2 ± 0.5 ohms.cm² (n=128). Values ranged between 2.5 and 34.8 ohms.cm². The Rs of axons with low membrane resistance (Rm < 1500 ohms.cm²) increased an average of 30% when stimulated for 45 sec to 7 min (50Hz) whereas the Rs of high Rm (Rm > 1500 ohms.cm²) axons decreased by an average of 10%. Carbachol (10-⁷M) caused the Rs of low Rm axons to decrease during stimulation but had no effect on high Rm axons. D-tubocurarine (10"⁸M) caused the Rs of high Rm axons to increase during stimulation but had no effect on low Rm axons. Bumetanide, a Na-K-Cl co-transport inhibitor and low (1/3 X normal) K+o, prevented the stimulation-induced increase in Rs of low Rm axons but had no effect on high Rm axons. Axons subjected to anisosmotic physiological solution in the range of 23 to 175% of isosmolar solution demonstrated that Rs of axons changes in a manner similar to that expected for a volume change in isolated cells. In hyperosmotic solution the Rs changes biphasically, initially decreasing then recovering, similar to regulatory volume changes described for glial cells in culture. The increase in Rs following the initial decrease is inhibited by bumetanide. Ouabain (10-³M), an inhibitor of the cell volume decreasing Na-K pump, causes the Rs to increase significantly above that seen for the no drug control. Bumetanide, an inhibitor of the volume increasing Na-K-Cl co-transporter, inhibits the volume regulatory response to anisosmotic media. Treating the axon with 3 X normal K+o causes the Rs to decrease approximately 15% while 5 X normal K+o leads to a 15% increase in Rs. Both ouabain and d-tubocurarine prevent the 3 X normal K+o-induced decrease in Rs while carbachol has little effect. On the other hand ouabain enhances the 5 X normal K+o-induced increase in Rs while carbachol and bumetanide inhibit this response. D-tubocurarine has little effect on the 5 X normal K+o-induced increase in Rs. The study demonstrates that changes in Rs are a reflection of changes in glial cell volume modulated by the ouabain- and bumetanide-sensitive potassium uptake mechanisms. The effects of carbachol and d-tubocurarine on the Rs suggest that their effects are modulated by the glial cell membrane potential and the electrochemical gradient for potassium, which in turn controls the amount of potassium that appears in the perineural space. It is proposed that the Rs of axons varies in response to the activity of the glial potassium uptake mechanisms stimulated by the appearance of potassium in the perineural space during action potential generation. The direction of the change in Rs during stimulation is a function of which potassium uptake mechanism (bumetanide-sensitive or ouabain-sensitive) dominates which in turn is dependent on the quantity perineural potassium and the action of the glial cell cholinergic system on the electrochemical gradient for potassium. |
| General note | Submitted to the faculty of the Department of Biology. |
| General note | Advisor: Gerhard W. Kalmus |
| Dissertation note | M.S. East Carolina University 1988 |
| Bibliography note | Includes bibliographical references (leaves 107-115). |
| Genre/form | dissertations. |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |