Although it is widely accepted that the electrical resonance seen in many types of auditory and vestibular hair cells contributes to frequency selectivity in these sensory systems, unexplained discrepancies in the frequency (f) and sharpness (Q) of tuning have raised serious questions. For example, enzymatically dissociated hair cells from bullfrog (Rana catesbeiana) sacculus resonate at frequencies well above the range of auditory and seismic stimuli to which the sacculus is most responsive. Such disparities, in addition to others, have led to the proposal that electrical resonance alone cannot account for frequency tuning. Using grassfrog (Rana pipiens) saccular hair cells, we show that the reported discrepancies in f and Q in this organ can be explained by the deleterious effects of enzyme (papain) exposure during cell dissociation. In patch-clamp studies of hair cells in a semi-intact epithelial preparation, we observed a variety of voltage behaviors with frequencies of 35-75 Hz. This range is well below the range of resonant frequencies observed in enzymatically dissociated hair cells and more in tune with the frequency range of natural stimuli to which the sacculus is maximally responsive. The sharpness of tuning also agreed with previous studies using natural stimuli. In contrast to results from enzymatically dissociated hair cells, both a calcium-activated K+ (KCa) current and a voltage-dependent K+ (KV) current contributed to the oscillatory responses of hair cells in the semi-intact preparation. The properties of the KCa and the Ca2+ current were altered by enzymatic dissociation. KV and a small-conductance calcium-activated K+ current were apparently eliminated.

Using a semi‐intact epithelial preparation we examined the Ca2+‐activated K+ (KCa) currents of frog (Rana pipiens) saccular hair cells. After blocking voltage‐dependent K+ (KV) currents with 4‐aminopyridine (4‐AP) an outward current containing inactivating (Itransient) and non‐inactivating (Isteady) components remained. The contribution of each varied greatly from cell to cell, with Itransient contributing from 14 to 90 % of the total outward current. Inactivation of Itransient was rapid (τ≈ 2–3 ms) and occurred within the physiological range of membrane potentials (V1/2=−63 mV). Recovery from inactivation was also rapid (τ≈ 10 ms). Suppression of both Itransient and Isteady by depolarizations that approached the Ca2+ equilibrium potential and by treatments that blocked Ca2+ influx (application Ca2+‐free saline or Cd2+), suggest both are Ca2+ dependent. Both were blocked by iberiotoxin, a specific blocker of large‐conductance KCa channels (BK), but not by apamin, a specific blocker of small‐conductance KCa channels. Ensemble‐variance analysis showed that Itransient and Isteady flow through two distinct populations of channels, both of which have a large single‐channel conductance (∼100 pS in non‐symmetrical conditions). Together, these data indicate that both Itransient and Isteady are carried through BK channels, one of which undergoes rapid inactivation while the other does not. Inactivation of Itransient could be removed by extracellular papain and could later be restored by intracellular application of the ‘ball’ domain of the auxiliary subunit (β2) thought to mediate BK channel inactivation in rat chromaffin cells. We hypothesize that Itransient results from the association of a similar β subunit with some of the BK channels and that papain removes inactivation by cleaving extracellular sites required for this association.