In:
The Journal of Neuroscience, Society for Neuroscience, Vol. 26, No. 39 ( 2006-09-27), p. 9944-9955
Abstract:
In hair cells of the inner ear, robust Ca 2+ /H + exchange mediated by plasma-membrane Ca 2+ -ATPase would rapidly acidify mechanically sensitive hair bundles without efficient removal of H + . We found that, whereas the basolateral membrane of vestibular hair cells from the frog saccule extrudes H + via an Na + -dependent mechanism, bundles rapidly remove H + in the absence of Na + and HCO 3 − , even when the soma is acidified. K + was fully effective and sufficient for H + removal; in contrast, Rb + failed to support pH recovery. Na + /H + -exchanger isoform 1 (NHE1) was present on hair-cell soma membranes and was likely responsible for Na + -dependent H + extrusion. NHE6 and NHE9 are organellar isoforms that can appear transiently on plasma membranes and have been proposed to mediate K + /H + exchange. We identified NHE6 in a subset of hair bundles; NHE9 was present in all bundles. Heterologous expression of these isoforms in yeast strains lacking endogenous exchangers conferred pH-dependent tolerance to high levels of KCl and NaCl. NHE9 preferred cations in the order K + , Na + ≫ Rb + , consistent with the relative efficacies of these ions in promoting pH recovery in hair bundles. Electroneutral K + /H + exchange, which we propose is performed by NHE9 in hair bundles, exploits the high-K + endolymph, responds only to pH imbalance across the bundle membrane, is unaffected by the +80 mV endocochlear potential, and uses mechanisms already present in the ear for K + recycling. This mechanism allows the hair cell to remove H + generated by Ca 2+ pumping without ATP hydrolysis in the cell.
Type of Medium:
Online Resource
ISSN:
0270-6474
,
1529-2401
DOI:
10.1523/JNEUROSCI.2990-06.2006
Language:
English
Publisher:
Society for Neuroscience
Publication Date:
2006
detail.hit.zdb_id:
1475274-8
SSG:
12
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