| First Author | Hill JK | Year | 2006 |
| Journal | J Neurosci | Volume | 26 |
| Issue | 39 | Pages | 9944-55 |
| PubMed ID | 17005858 | Mgi Jnum | J:331349 |
| Mgi Id | MGI:7387161 | Doi | 10.1523/JNEUROSCI.2990-06.2006 |
| Citation | Hill JK, et al. (2006) Vestibular hair bundles control pH with (Na+, K+)/H+ exchangers NHE6 and NHE9. J Neurosci 26(39):9944-55 |
| abstractText | In hair cells of the inner ear, robust Ca2+/H+ exchange mediated by plasma-membrane Ca2+-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 HCO3(-), 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 Ca2+ pumping without ATP hydrolysis in the cell. |
