Effects of mitochondrial uncouplers on intracellular calcium, pH and membrane potential in rat carotid body type I cells.
1. Mitochondrial uncouplers are potent stimulants of the carotid body. We have therefore investigated their effects upon isolated type I cells. Both 2,4-dinitrophenol (DNP) and carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP) caused an increase in [Ca2+]i which was largely inhibited by removal of extracellular Ca2+ or Na+, or by the addition of 2 mM Ni2+. Methoxyverapamil (D600) also partially inhibited the [Ca2+]i response. 2. In perforated-patch recordings, the rise in [Ca2+]i coincided with membrane depolarization and was greatly reduced by voltage clamping the cell to -70 mV. Uncouplers also inhibited a background K+ current and induced a small inward current. 3. Uncouplers reduced pHi by 0.1 unit. Alkaline media diminished this acidification but had no effect on the [Ca2+]i response. 4. FCCP and DNP also depolarized type I cell mitochondria. The onset of mitochondrial depolarization preceded changes in cell membrane conductance by 3-4 s. 5. We conclude that uncouplers excite the carotid body by inhibiting a background K+ conductance and inducing a small inward current, both of which lead to membrane depolarization and voltage-gated Ca2+ entry. These effects are unlikely to be caused by cell acidification. The inhibition of background K+ current may be related to the uncoupling of oxidative phosphorylation.
Buckler
K J
KJ
University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK. keith.buckler@physiol.ox.ac.uk
Vaughan-Jones
R D
RD
D019297:2,4-Dinitrophenol / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002344:Carotid Body / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D005711:Gallopamil / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010085:Oxidative Phosphorylation / Q000187:drug effects; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D014475:Uncoupling Agents / Q000494:pharmacology*
D015221:Potassium Channels; D014475:Uncoupling Agents; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D005711:Gallopamil; D019297:2,4-Dinitrophenol