Gaseous Transmitter Regulation of Catecholamine Secretion by hypoxia in Murine Adrenal Chromaffin Cells

Emerging evidence suggests that gaseous molecules, carbon monoxide (CO) and hydrogen sulfide (H2S) generated by heme oxygenase-(HO)-2 and cystathionine γ-lyase (CSE), respectively, function as transmitters in the nervous system. Present study examined the roles of CO and H2S in hypoxia-induced catecholamine (CA) release from adrenal medullary chromaffin cells (AMC). Studies were performed on AMC from adult (≥6 weeks of age) wild type (WT), HO-2 null, CSE null and HO-2/CSE double null mice of either gender. CA secretion was determined by carbon fiber amperometry and [Ca2+]i by microflurometry using Fura-2. HO-2- and CSE immunoreactivities were seen in WT AMC, which were absent in HO-2 and CSE null mice. Hypoxia (medium pO2 30-38 mmHg) evoked CA release and elevated [Ca2+]i. The magnitude of hypoxic response was greater in HO-2 null mice and in HO inhibitor treated WT AMC compared to controls. H2S levels were elevated in HO-2 null AMC. Either pharmacological inhibition or genetic deletion of CSE prevented the augmented hypoxic responses of HO-2 null AMC and H2S donor rescued AMC responses to hypoxia in HO-2/CSE double null mice. CORM-3, a CO donor, prevented the augmented hypoxic responses in WT and HO-2 null AMC. CO donor reduced H2S levels in WT AMC. The effects of CO donor were blocked by either ODQ or 8pCT, inhibitors of soluble guanylyl cyclase (SGC) or protein kinase G, respectively. These results suggest that HO-2-derived CO inhibits hypoxia-evoked CA secretion from adult murine AMC involving soluble guanylyl cyclase (SGC)-protein kinase G (PKG)-dependent regulation of CSE- derived H2S.