Cytochrome b558 (p22phox) in the guinea-pig adrenal medulla

Paraganglionic cells are sensitive to hypoxia, and the involvement of a pla smalemmal cytochrome b558-like protein in oxygen sensing by these cells has been suggested, but neither the identity of the immunoreactive protein det ected by immunohistochemistry nor its anticipated subcellular (i.e., plasma lemmal) localization were directly proven. Thus, we extended these studies to the largest paraganglion, i.e., the adrenal medulla, in the guinea-pig, which, due to its size and accessibility, allowed us to address both of the se issues utilizing antisera raised against synthetic peptides of the small (22 kD) subunit of cytochrome b558, p22phox. Cytochrome b558 was originall y identified in granulocytes and macrophages, and antisera against this pha gocyte p22phox were utilized. Immunoreactivity to p22phox was observed in a ll adrenal medullary endocrine cells, and the identity of the immunoreactiv e protein to the small cytochrome b558-subunit was confirmed by Western blo tting. Immune-electron microscopy of ultrathin cryosections and of resin-em bedded tissue demonstrated its subcellular localization in the dense core v esicles of endocrine A-cells but not in the plasma membrane. In conclusion, the present study documents the presence of the small subunit of cytochrom e b558 in guinea-pig adrenal medullary cells, but its subcellular vesicular localization does not support the initial interpretation of cytochrome b55 8 serving as a plasmalemmal oxygen sensor. (C) 1999 Wiley-Liss, Inc.