Relative mitochondrial membrane potential and Ca2+i in type I cells isolated from the rabbit carotid body.

In the accompanying paper (Duchen FCCP) increased fluorescence by up to 80-120%, while fluorescence was reduced by blockade of the F0 proton channel of the mitochondrial ATP synthase complex (oligomycin). 3. delta psi m depolarized rapidly with anoxia, and was usually completely dissipated within 1-2 min. The depolarization of delta psi m with anoxia (or CN-) and repolarization on reoxygenation both followed a time course well characterized as the sum of two exponential processes. Oligomycin (0.2-2 micrograms/ml) hyperpolarized delta psi m and abolished the slower components of both the depolarization with anoxia and of the subsequent repolarization. These data (i) illustrate the role of the F1-F0 ATP synthetase in slowing the rate of dissipation of delta psi m on cessation of electron transport, (ii) confirm blockade of the ATP synthetase by oligomycin at these concentrations, and (iii) indicate significant accumulation of intramitochondrial ADP during 1-2 min of anoxia. 4. Depolarization of delta psi m was graded with graded changes in PO2 below about 60 mmHg. The stimulus-response curves thus constructed strongly resemble those for Ca2+i and NAD(P)H with PO2. The change in delta psi m closely followed changes in PO2 with time. 5. The rate of rise of Ca2+i in response to anoxia is strongly temperature sensitive. The rate of depolarization of delta psi m with anoxia similarly increased at least two- to fivefold on warming from 22 to 36 degrees C. The change with FCCP was not significantly altered by temperature. 6. These data show that the mitochondrial membrane potential changes over a physiological range of PO2 values in type I cells. This contrasts with the behaviour in dissociated chromaffin cells and sensory neurons, in which no change was measurable until the PO2 fell close to zero.(ABSTRACT TRUNCATED AT 400 WORDS)