Na('+)-Li('+) countertransport is apparently responsible for the fact that the concentration of Li('+) inside Li('+)-treated red blood cells is less than expected for a passive distribution. It has been suggested that a similar countertransport mechanism should be found in nervous tissue. In this study, I examined whether countertransport or the ouabain-sensitive Na('+)-K('+) pump maintains the transmembrane Li('+) gradient in Li('+)-treated olfactory nerves from garfish (Lepisosteus osseus). I also examined how phloretin changes transmembrane distributions of monovalent cations and nerve excitability. From the results, I find that Li('+) apparently is distributed nonpassively in the olfactory nerve, since the ratio of Li('+) (,i)/ Li('+) (,o) across axons is 1.5-2.1. A ratio of 10:1 expected for a passive distribution at an assumed membrane potential of -60 mV. The nonpassive gradient for Li('+) is phloretin-sensitive, ouabain-insensitive, and Na('+)-dependent. Thus, the mechanism maintaining this gradient may be an Na('+)-Li('+) countertransport similar to that postulated for RBC. Transmembrane Na('+) and K('+) gradients also decrease in solutions containing high concentrations of phloretin, probably due to a phloretin-induced increase in membrane permeability to cations. Low concentrations of phloretin (0-50 uM) decrease impulse velocity, action potential magnitude, and rheobasic threshold, and increase the membrane time constant, of the nerve. At short stimulus durations, excitation threshold in phloretin increases, and at long durations, it decreases. Comparisons of electrophysiological effects between 0-50 mM phloretin and 0-50 mM LiCl (from earlier investigations) suggests that phloretin decreases nerve excitability by decreasing membrane conductances to Na('+) and K('+), while Li('+) decreases excitability by blocking the Na('+)-K('+) pump and / decreasing transmembrane Na('+) gradients. Two major contributions of this work are the presentation of evidence for Na('+)-Li('+) countertransport in axons, and examination of the effects of phloretin on the propagated nerve impulse. / Source: Dissertation Abstracts International, Volume: 46-04, Section: B, page: 1079. / Thesis (Ph.D.)--The Florida State University, 1985.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_75572 |
| Contributors | ROBERTS, EUGENE L., JR., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 271 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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