Modeling channel properties in vestibular calyx terminals

Two types of hair cell have been described in the vestibular end organs of amniotes, but the coding of sensory signals by different hair cell types is not well understood. Type I hair cells are contacted by cup-shaped afferent calyx terminals, whereas type II hair cells are contacted by bouton terminals. The whole cell patch-clamp technique has been used to record voltage-dependent ionic currents from calyx terminals. Type I hair cells along with their calyces were non-enzymatically dissociated from the semicircular canals and utricles of Mongolian gerbils. Voltage-dependent currents identified in whole cell voltage-clamp included transient inward sodium currents and outward potassium currents. Potassium currents were pharmacologically blocked by cesium in the patch electrode solution. The NEURON simulation environment was used to model the properties of the calyx terminal. A series of interconnected cylindrical compartments was designed to represent the inner and outer calyx membrane, the base of the calyx and a short axon segment. Kinetic parameters for the Na+ current were optimized with a genetic algorithm to match kinetic data from the whole cell recordings.