Sodium entry pathways in isolated goldfish hair cells

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

Department dc:contributor.department

Harvard University--MIT Division of Health Sciences and Technology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Ronan, Diane Elizabeth, 1970-

Advisor dc:contributor.advisor

• Edmund A. Mroz.

• Harvard University--MIT Division of Health Sciences and Technology.

Statement dc: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.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/28599

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/28599