Sensory hair cells transduce mechanical information into electrical signals through mechanically gated ionic channels which is called as the mechano-electrical transduction (MET) channels. The mechanical displacement of the hair bundle towards the taller stereocilia generates inward-going MET currents. This currents generate depolarizing transduction potential which are transmitted to the central nervous system for further information processing. The angular displacement of the hair bundle is the primary factor in the gating of MET channel. The wide variety of monovalent cations including small organic cations and divalent cations were permeable through the MET channel (non-selective cation channel). Ca2+ permeability was about four times by monovalent cations. The single channel conductance of the MET determined by the step-like single channel currents was 50-100 pS. There are two hypothesis about the site of the MET channels; one is the base of the hair bundle and the other is the top of the hair bundle. The adaptation of the MET current was observed when steady displacement was applied to the hair bundle. Adaptation was dependent on the membrane potential and only observed in inward-going MET currents. Ca2+ influx through the MET channel is associated to the adaptation.