Outward currents from hair cells from the horizontal semicircular canal (HSCC) of the toadfish were investigated using whole cell patch clamp methods. Two classes of hair cells are found. One class (approx. 10% of cells) showed only a non-inactivating current (IKCa) which was blocked by 2 mM TEA. A second class had both inactivating and non-inactivating currents. The former (IA) was blocked by 4-AP (1 mM) and the latter (IKCa) by TEA (2- 20 mM). While the majority of the cells expressed both these outward currents, due to IA inactivation both currents are functionally present in the same cell only between -60 and -40 mV. At more depolarized membrane potentials, IA was inactivated, suggesting that a single hair cell may have two distinct signalling modes, one dominated by IA at more hyperpolarized membrane potentials and the other by IKCa at depolarized values where ICa is beginning to grow, increasing both amplitude and activation rate of IKCa. The switch between modes will be determined by the amplitude and frequency characteristics of the stimulus and possibly also by actions of efferent transmitters. In current clamp mode, 10% of the HSCC hair cells showed high Q and high frequency resonance, from 44 to 360 Hz at 12°C. These cells expressed only one outward calcium dependent, non-inactivating, TEA sensitive current, characteristic of IKCa. A suggested role for high frequency resonance is as positive feedback to produce a high frequency updating of the stereociliary compliance to most faithfully transduce angular acceleration.
Bibliographical noteFunding Information:
This work was carried out at the Marine Biological laboratory in Woods Hole, MA and supported by NSF 9120497 (A.S.) and NIMH MH 48190 (J.M. and R.P.). The authors wish to thank Drs. Conchita Zuazaga and Lucia Tabares for their help with the manuscript and Stephen M. Highstein for the photograph of the HSCC hair cells in Fig. 8.
- A current
- Calcium activated potassium current
- Patch clamp analysis
- Potassium current
- Sensory hair cells
- Vestibular system