Cell-specific expression of theα9 n-ACh receptor subunit in auditory hair cells revealed by single-cell RT-PCR

Single-cell reverse transcription polymerase chain reaction was carried out in three different cell types from the organ of Corti of the four-day old rat. For this purpose, pieces of the organ of Corti were mounted under a differential-interference contrast video microscope. Two different mounting configurations were used to allow imaging of cells from two almost orthogonal angles. This method afforded unequivocal recognition of various cell types in the vital tissue, and extraction of nucleus and cytoplasm of specified individual cells with a patch pipette. Messenger RNA encoding the $\alpha $9 acetylcholine (ACh) receptor subunit was detected and sequenced from individual outer hair cells and inner hair cells, but was not found in Deiters' cells. The identical Deiters' cells were positive for a P$_{2\text{X}}$ receptor subunit. This indicates cell-specific expression of the $\alpha $9 subunit in inner hair cells and outer hair cells and supports the hypothesis that this subunit contributes to calcium (Ca$^{2+}$) permeable ionotropic ACh receptors (ACh-R). ACh-dependent Ca$^{2+}$ concentration increase has been observed in both outer hair cells and inner hair cells.