Heme oxygenase-1 (HO-1) mediated respiratory responses to hypoxia in the goldfish, Carassius auratus.

In this study we investigated the role of heme oxygenase-1 (HO-1) in modulating the hypoxic and hyperoxic ventilatory responses of goldfish (Carassius auratus) acclimated to 7 and 25°C. HO-1 was present in the neuroepithelial cells (NECs; putative branchial O2 chemoreceptors) of fish acclimated to 7°C only. Hypoxia exposure increased gill HO-1 activity in 7°C fish (14.0±1.4 to 42.5±3.2pmolbilirubinmin(-1)mgprotein(-1)). Inhibition of HO-1 activity with zinc protophorphyrin IX (ZnPPIX) increased the ventilation frequency response to acute hypoxia (30mmHg); frequency increased from 48.3±5.1 to 137.4±16.0 breaths per min (BPM) in hypoxic 7°C fish treated with ZnPPIX compared to 46.2±4.2 to 77.9±5.3 BPM in control fish. Unlike in the control (untreated) 7°C fish exposed to hyperoxia, fish injected with ZnPPIX did not significantly decrease breathing frequency. Inhibiting HO-1 activity was without effect on the hypoxic or hyperoxic ventilatory responses of fish acclimated to 25°C. Based on these observations, we suggest that HO-1 plays an inhibitory role in regulating breathing frequency but only in goldfish acclimated to 7°C.