Previous results indicate that the functional properties of myelinated axons are considerably more complex than previously believed. The purpose of this study was to further examine the functional properties of potassium conductances in dorsal and ventral root (DRA; VRA) frog myelinated axons by intracellular microelectrode recording. The voltage responses to hyperpolarizing current injection demonstrated: (1) a nonlinear voltage current (V/I) relationship in the region just below resting membrane potential; (2) a linear peak and steady state V/I relationship below $ approx$ $-$95 mV; (3) a large effective capacitance of the internodal membrane; and (4) an attenuation of the voltage response reflecting the activation of a voltage dependent anomalous rectifying conductance (G$ sb{ rm AR}$). G$ sb{ rm AR}$ is dependent on the presence of sodium and potassium ions in the external medium and is blocked by cesium but not barium ions. (5) An afterhyperpolarizing potential (AHP) after a train of action potentials was accounted for by the presence of a sodium dependent potassium conductance (G$ sb{ rm K(Na)}$). The functional role of the voltage dependent potassium conductances and G$ sb{ rm K(Na)}$ was examined. G$ sb{ rm AR}$ appears to regulate the length of a post tetanic AHP. Early accommodation (EAcc) is regulated by G$ sb{ rm Kf1}$ in DRA and VRA. Late accommodation (LAcc) and adaptation (Adp) is regulated by G$ sb{ rm Ks}$ in both DRA and VRA. G$ sb{ rm Kf2}$ may also contribute to EAcc and Adp. Action potential repolarization in DRA and VRA is governed by G$ sb{ rm Kf2}$ and G$ sb{ rm Kf1}$ respectively. G$ sb{ rm K(Na)}$ may also contribute to LAcc and Adp. An evaluation of our experimental results using a computer model based Hodgkin-Huxley type equations suggests that the gating of the sodium conductance plays only a minor role in accommodation and adaptation. These results indicate that potassium conductances play a pivotal role in regulating the excitabilit
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.74560 |
| Date | January 1990 |
| Creators | Poulter, Michael Owen |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Pharmacology and Therapeutics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001116115, proquestno: AAINN66467, Theses scanned by UMI/ProQuest. |
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