Effects of mitochondrial uncouplers on intracellular calcium, pH and membrane potential in rat carotid body type I cells

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 [Ca 2+ ] i which was largely inhibited by removal of extracellular Ca 2+ or Na + , or by the addition of 2 m m Ni 2+ . Methoxyverapamil (D600) also partially inhibited the [Ca 2+ ] i response. In perforated-patch recordings, the rise in [Ca 2+ ] 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. Uncouplers reduced pH i by 0.1 unit. Alkaline media diminished this acidification but had no effect on the [Ca 2+ ] i response. FCCP and DNP also depolarized type I cell mitochondria. The onset of mitochondrial depolarization preceded changes in cell membrane conductance by 3–4 s. 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 Ca 2+ 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.