Electrophysiological responses of dissociated type I cells of the rabbit carotid body to cyanide.
1. The carotid body is the major peripheral sensor of arterial PO2 in the mammal and is excited by cyanide (CN-). Type I cells, the presumed sites for transduction, were freshly dissociated from the carotid body of the adult rabbit and studied with the whole-cell patch clamp technique. 2. Type I cells were hyperpolarized by CN-, the action potential was shortened, and there was an increased after-hyperpolarization. 3. Under voltage clamp control, CN- increased a voltage-dependent outward current, which showed pronounced outward rectification. Tail currents increased by CN- reversed close to the predicted EK, the reversal potential of the CN--induced current depended on extracellular [K+], and the current was blocked by intracellular TEA+ and Cs+. 4. The i-V relation of the CN--induced conductance strongly mirrored that of voltage-gated Ca2+ entry, and the response was abolished by removal of extracellular Ca2+. We conclude that the increased gK is Ca2+ -dependent (gK(Ca]. 5. The Ca2+ current was attenuated by CN-, and showed an increased rate of inactivation. Thus, the increased gK(Ca) must result from an alteration in Ca2+ homeostasis independent of the Ca2+ current, and not an increased Ca2+ entry through voltage-activated channels. 6. Carbachol also hyperpolarized cells and increased a K+ conductance. 7. At depolarized holding potentials a steady-state outward current was increased by CN-. The current reversed close to EK, and was associated with increased current fluctuations. Noise analysis showed that a channel conductance of 3 pS carries the current. 8. The response to CN- was not impaired by the inclusion of 5 mM-MgATP in the patch pipette. 9. If signals to the CNS are initiated by the calcium-dependent release of transmitters from type I cells, transduction would appear to be the direct consequence of the energy dependence of Ca2+ homeostasis.
Biscoe
T J
TJ
Department of Physiology, University College London.
Duchen
M R
MR
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D002344:Carotid Body / Q000166:cytology / Q000187:drug effects*; D003486:Cyanides / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D011817:Rabbits; D012966:Sodium Cyanide / Q000494:pharmacology*
D015220:Calcium Channels; D003486:Cyanides; D002217:Carbachol; D012966:Sodium Cyanide