PROPERTIES OF A TRANSIENT K+ CURRENT IN CHEMORECEPTOR CELLS OF RABBIT CAROTID-BODY

1. Adult rabbit carotid body chemoreceptor cells, enzymatically dispersed and short-term cultured, exhibit an inactivating outward K+ current that is reversibly inhibited by low P(O2). In the present work we have characterized the biophysical and pharmacological properties of this current using the whole-cell voltage clamp recording technique. 2. Inactivating current was recorded after blockage of Ca2+ currents with extracellular Co2+, Cd2+, or after complete washing out of Ca2+ channels. 3. The threshold of activation of this inactivating current was about -40 mV. Current activated very quickly (mean rise time 4-8 +/- 0-42 ms at +60 mV) but inactivated more slowly. Inactivation was well fitted by two exponentials with time constants of 79-7 +/- 6.6 and 824 +/- 42-8 ms (at +40 mV). The inactivation process showed a little voltage dependence. 4. The steady-state inactivation was well fitted by a Boltzman function. Inactivation was fully removed at potentials negative to -80 mV and was complete at voltages near -10 mV; 50 % inactivation occurred at -41 mV. 5. Recovery from inactivation had several components and was voltage dependent. Initial recovery was fast, but full recovery, even at -100 mV, required more than 30 s. 6. Inactivating current was selectively blocked by 4-aminopyridine (4-AP), in a dose-dependent manner (IC50, 0-2 mm). The duration of chemoreceptor cells action potentials was augmented by 1 mm 4-AP from 2-3 +/- 0-36 to 7.0 +/- 0-25 ms at 0 mV. Tetraethylamonium (TEA), at concentrations above 5 mm, blocked inactivating and non-inactivating components of the whole K+ current. 7. Inactivating current was modulated by cyclic AMP (cAMP). Bath application of 2 mm dibutyryl cAMP reduced peak amplitude by 18.7 +/- 2.9 % (at +30 mV) and slowed down the rise time of the current. The effect was not voltage dependent. Forskolin (10-20 mum) also affected inactivating current, by accelerating the inactivation process. In the same preparations neither dibutyryl cAMP nor forskolin affected Ca2+ currents. 8. It is concluded that modulation of K+ channels by cAMP might play a physiological role potentiating the low P(O2) inhibition of K+ channels.