The receptor potential in type I and type II vestibular system hair cells: a model analysis

Several studies have shown that type I hair cells present a large outward rectifying potassium current (g(K,L)) that is substantially activated at the resting potential, greatly reducing cell input resistance and voltage gain. In fact, mechanoelectrical transducer currents seem not to be large enough to depolarize type I hair cells to produce neurotransmitter release. Also, the strongly nonlinear transducer currents and the limited voltage oscillations found in some hair cells did not account for the bidirectionality of response in hair cell systems. We developed a model based in the analysis of nonlinear Goldman-Hodgkin-Katz equations to calculate the hair cell receptor potential and ionic movements produced by transducer current activation. Type I hair cells displaying the large g(K,L) current were found to produce small receptor potentials (3-13.8 mV) in response to mechanoelectrical transducer current input. In contrast, type II cells that lack g(K,L) produced receptor potentials of about 30 mV. Properties of basolateral ionic conductances in type II hair cells will linearize hair bundle displacement to receptor potential relationship. The voltage to obtain the half maximal activation of g(K,L) significantly affects the resting membrane potential, the amplitude, and the linearity of the receptor potential. Electrodiffusion equations were also used to analyze ionic changes in the intercellular space between type I hair cell and calyx endings. Significant K(+) accumulation could take place at the intercellular space depending on calyx structure.