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

Abstract

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 pH_i 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.