抄録
Phosphatidylinositol 4,5-bisphosphate (PIP2) regulates ion transporters and channels in addition to second messenger systems. Previous reports indicated that PIP2 is expressed in hair bundles, the mechanically sensitive organelle of hair cells. Whether PIP2 regulates mechanoelectrical transduction channels of hair cells has hitherto not been investigated. Therefore, we have characterized the distribution of PIP2 in hair bundles and determined a physiological role of PIP2 in transduction. According to our immunocytochemical data, hair cells from bullfrog sacculi expressed PIP2 in hair bundles, except on basal part of the hair bundles. This labeling disappeared when hair cells were treated with PI4-kinase inhibitors, phenylarsine oxide and quercetin, which block PIP2-replenishment. Reciprocal distribution of PIP2 and the lipid phosphatase Ptprq suggests why PIP2 is absent from stereocilia bases. Our whole-cell patch-clamp recording data from isolated hair cells show that adaptation of transduction currents became significantly slower when PIP2 was depleted with PI4-kinase inhibitors. In addition, in the bullfrog utricle, the central striolar hair cells, which adapt more rapidly to maintained hair bundle displacement, have much less Ptprq than peripherally located extrastriolar hair cells, which do not adapt or adapt only very slowly. These results suggest that differences in adaptation rate could arise from variations in the concentration of PIP2 in hair bundles. [Jpn J Physiol 54 Suppl:S169 (2004)]
