Mitochondrial function in type I cells isolated from rabbit arterial chemoreceptors.

Area of Science:

• Cell biology
• Neuroscience
• Physiology

Background:

• The carotid body is the primary peripheral arterial oxygen sensor.
• Mitochondrial electron transport's oxygen sensitivity is hypothesized to be the basis for carotid body transduction.
• Type I cells are the primary cells within the carotid body responsible for oxygen sensing.

Purpose of the Study:

• To investigate the changes in mitochondrial NAD(P)H autofluorescence in isolated type I cells in response to varying partial pressures of oxygen (PO2).
• To determine if the observed changes in mitochondrial autofluorescence are linked to intracellular calcium ([Ca2+]i) levels.
• To assess the role of mitochondrial electron transport in the oxygen-sensing mechanism of the carotid body.

Main Methods:

• Measurement of NAD(P)H autofluorescence (excitation 340-360 nm, emission peak 450 nm) in isolated type I cells under varying PO2 conditions.
• Comparison of responses to anoxia and cyanide to ascertain the mitochondrial origin of autofluorescence.
• Assessment of the relationship between hypoxia-induced mitochondrial changes, intracellular calcium ([Ca2+]i), and responses to K(+)-induced depolarization.
• Utilized carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP) to measure resting oxygen consumption.

Main Results:

• NAD(P)H autofluorescence increased with decreasing PO2, indicating altered mitochondrial function below approximately 60 mmHg.
• The hypoxia-induced mitochondrial changes were independent of the rise in intracellular calcium ([Ca2+]i).
• Responses in chromaffin cells and dorsal root ganglion neurons showed minimal autofluorescence changes until PO2 fell below 5 mmHg, highlighting the specific sensitivity of type I cells.

Conclusions:

• The oxygen sensitivity of mitochondrial electron transport in carotid body type I cells is a primary mechanism for arterial oxygen sensing.
• Mitochondrial NAD(P)H autofluorescence serves as a reliable indicator of oxygen-dependent changes in mitochondrial function.
• The observed hypoxia-induced mitochondrial responses are intrinsic to type I cells and not secondary to calcium influx.