■ OBJECTIVES: The voltage dependent Ca++ channels (VDCCs) play essential roles in excitable cells. However, the physiological properties of voltage-dependent Ca++ current in mature outer hair cells (OHCs) are still obscure. The expression of high-voltage activated L-type and R-type VDCC has reported, whereas the auditory hair cells have relatively lower resting potentials. We examined if low-voltage activated T-type calcium channels express in the rat auditory hair cells.

■ METHODS: To clarify the characteristics of the mature OHCs, we performed PCR, in situ hybridization, western blotting and immunohistochemistry with the rat mature cochleae.

■ RESULTS: The mRNA expression of each T-type Ca++ channels were examined using a reverse transcription (RT)-PCR technique. Positive signals were detected with primers of CaV3.1, but were not detected with primers of CaV3.2 and CaV3.3. In situ hybridization study showed localization of CaV3.1 in inner and outer hair cells. Immunoblot analyses with membrane extracts from mature cochleae were performed, using an anti-CaV3.1 antibody. The antibody recognized a single ~242 kDa band.  Immunohistochemistry with the same antibody showed localization of CaV3.1 in OHCs lateral membrane. We concluded that both inner and outer hair cells expressCaV3.1 at the mRNA level, but only OHCs expresses CaV3.1 at the protein level.