Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2003. / Includes bibliographical references (leaves 126-136). / Hair cells are the exquisitely-sensitive mechanosensory transducers of the inner ear. While the electrophysiology of hair cells has been extensively studied, little is known about the vital background processes that maintain the steady-state intracellular ionic environment. This study explored Na-coupled ion transport processes in isolated goldfish hair cells both in the steady state and in response to perturbations. Intracellular Na⁺ concentration ([Na⁺]i) and pH (pHi) were measured using the fluorescent probes SBFI and BCECF, respectively. The total steady-state Na⁺ entry, determined by measuring the initial rate of increase in [Na⁺]i during inhibition of Na⁺,K⁺-ATPase, was 9 mM/min, a rate higher than in many other epithelial cells involved in rapid ion transport. To uncover the entry pathways for such a high Na⁺ influx, pharmacological agents and manipulations of extracellular composition were used to dissect apart the contributions of various transporters or channels. A combination of Na⁺ entry via transduction channels, the Na⁺/H⁺ exchanger, and the Na⁺/Ca²⁺ exchanger accounted for 3/4 of the total steady-state Na⁺ entry. Consistent with a significant component via the Na⁺/Ca²⁺ exchanger, nifedipine, a blocker of L-type calcium channels, also reduced the Na⁺ entry rate. Since the Na⁺/H⁺ exchanger in goldfish hair cells, in contrast to many other cell types, displayed significant activity in the steady state, interactions between regulation of [Na⁺]i and pHi were examined during recovery from intracellular acid loads. The rate of Na+ entry or acid extrusion via the Na⁺/H⁺ exchanger increased by a factor of 6 during recovery from an acid load. In most cells, [Na⁺]i doubled after the acid load and subsequently recovered, even though the / (cont.) was not exogenously inhibited. These results indicate that intracellular acidification inhibits the Na⁺, K⁺-ATPase, and therefore poses a potential conflict for maintenance of intracellular Na⁺ homeostasis. Although hair cells were traditionally described as passive resistors, this thesis demonstrates that goldfish hair cells have a significant metabolic load, even in the steady state, arising from the activities of specific Na⁺-coupled transporters and channels. Under certain pathophysiological circumstances, such as ischemia or acoustic trauma, increased Na⁺ influx via these pathways may overwhelm the ion-homeostatic capabilities of hair cells. / by Diane Elizabeth Ronan. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/28599 |
| Date | January 2003 |
| Creators | Ronan, Diane Elizabeth, 1970- |
| Contributors | Edmund A. Mroz., Harvard University--MIT Division of Health Sciences and Technology., Harvard University--MIT Division of Health Sciences and Technology. |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | 136 leaves, 6167036 bytes, 6184108 bytes, application/pdf, application/pdf, application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/7582 |
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