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 PO2. 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 microM) 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 PO2 inhibition of K+ channels.
Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid, Spain.
J R
JR
López-López
D A
DA
De Luis
C
C
Gonzalez
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002344:Carotid Body / Q000166:cytology / Q000378:metabolism*; D002478:Cells, Cultured; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007477:Ions; D008564:Membrane Potentials / Q000502:physiology; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*
D007477:Ions; D005576:Colforsin; D003994:Bucladesine; D015761:4-Aminopyridine; D000242:Cyclic AMP; D000254:Sodium-Potassium-Exchanging ATPase