Functional mitochondria are required for O2 but not CO2 sensing in immortalized adrenomedullary chromaffin cells

Catecholamine (CAT) release from adrenomedullary chromaffin cells (AMC) in response to stressors such as low O-2 (hypoxia) and elevated CO2/ H+ is critical during adaptation of the newborn to extrauterine life. Using a surrogate model based on a v- myc immortalized adrenal chromaffin cell line (i. e., MAH cells), combined with genetic perturbation of mitochondrial function, we tested the hypothesis that functional mitochondria are required for O-2 sensing. Wild- type MAH cells responded to both hypoxia and increased CO2 (hypercapnia) with K (+) current inhibition and membrane depolarization. Additionally, these stimuli caused a rise in cytosolic Ca2+ and CAT secretion, determined by fura- 2 spectrofluorimetry and carbon fiber amperometry, respectively. In contrast, mitochondria- deficient (rho(0)) MAH cells were hypoxia insensitive, although responses to hypercapnia and expression of several markers, including carbonic anhydrase II, remained intact. Rotenone (1 mu M), a mitochondrial complex I blocker known to mimic and occlude the effects of hypoxia in primary AMC, was effective in wild- type but not rho(0) MAH cells. These data demonstrate that functional mitochondria are involved in hypoxia- sensing by adrenal chromaffin cells. We also show for the first time that, like their neonatal chromaffin cell counterparts, MAH cells are CO2 sensors; however, this property is independent of functional mitochondria.