Developmental regulation of O₂ sensing in neonatal adrenal chromaffin cells from wild-type and NADPH-oxidase-deficient mice

Abstract.

In mammals, adrenomedullary chromaffin cells (AMC) express a neutrophil-like NADPH oxidase and secrete catecholamines, which play a vital role in the ability of the neonate to survive hypoxic stress. To test whether NADPH oxidase functions as an O₂ sensor, and whether mouse AMC express a developmentally regulated O₂-sensing mechanism similar to rats, we compared the effects of hypoxia on cultured AMC from wild-type (WT) and transgenic oxidase-deficient (OD) mice, lacking the gp91^phox subunit of NADPH oxidase. Hypoxia (pO₂ ≅5 mmHg) caused a reversible inhibition of outward K⁺ current by ≅27% (n=6) in WT and ≅29% (n=9) in OD neonatal (P1-P5) chromaffin cells. O₂-sensitive K⁺ currents included both Ca²⁺-dependent (I _BK) and a delayed rectifier-like K⁺ current (I _KV). Additionally, hypoxia depolarized WT and OD chromaffin cells and caused reversible broadening of the action potential. Exposure of both WT and OD neonatal AMC cultures to hypoxia (5% O₂) for ≅1 h caused four- to sixfold stimulation of catecholamine (CA) secretion as determined by HPLC. In contrast, hypoxia had no significant effect on K⁺ currents or CA secretion in juvenile (P14-P15) AMC. Thus, mouse AMC possess a developmentally regulated O₂-sensing mechanism, but NADPH oxidase does not function as the primary O₂ sensor in these cells.