A model of signal processing at the isolated hair cell of the frog semicircular canal.

A computational model has been developed to simulate the electrical behavior of the type II hair cell dissected from the crista ampullaris of frog semicircular canals. In its basolateral membrane, it hosts a system of four voltage-dependent conductances (g A , g KV , g KCa , g Ca ). The conductance behavior was mathematically described using original patch-clamp experimental data. The transient K current, IA, was isolated as the difference between the currents obtained before and after removing IA inactivation. The remaining current, IKD, results from the summation of a voltage-dependent K current, IKV, a voltage-calcium-dependent K current, IKCa, and the calcium current, ICa. IKD was modeled as a single lumped current, since the physiological role of each component is actually not discernible. To gain a clear understanding of its prominent role in sustaining transmitter release at the cytoneural junction, ICa was modeled under different experimental conditions. The model includes the description of voltage- and time-dependent kinetics for each single current. After imposing any starting holding potential, the system sets the pertinent values of the variables and continually updates them in response to variations in membrane potential. The model reconstructs the individual I-V curves obtained in voltage-clamp experiments and simulations compare favorably with the experimental data. The model proves useful in describing the early steps of signal processing that results from the interaction of the apical receptor current with the basolateral voltage-dependent conductances. The program is thus helpful in understanding aspects of sensory transduction that are hard to analyze in the native hair cell of the crista ampullaris.