KATP-channels play a minor role in the protective hypoxic shut-down of cerebellar activity in eider ducks (Somateria mollissima)

Eider duck (Somateria mollissima) cerebellar neurons are highly tolerant toward hypoxia in vitro, which in part is due to a hypoxia-induced depression of their spontaneous activity. We have studied whether this response involves ATP-sensitive potassium (KATP) channels, which are known to be involved in the hypoxic/ischemic defense of mammalian neural and muscular tissues, by causing hyperpolarization and reduced ATP demand. Extracellular recordings in the Purkinje layer of isolated normoxic eider duck cerebellar slices showed that their spontaneous neuronal activity decreased significantly compared to in control slices when the KATP channel opener diazoxide (600 μM) was added (F1,70 = 92.781, p < 0.001). Adding the KATP channel blocker tolbutamide (400 μM) 5 min prior to diazoxide completely abolished its effect (F1,55 = 39.639, p < 0.001), strongly suggesting that these drugs have a similar mode of action in this avian species as in mammals. The spontaneous activity of slices treated with tolbutamide in combined hypoxia/chemical anoxia (95% N2-5% CO2 and 2 mM NaCN) was not significantly different from that of control slices (F1,203 = 0.071, p = 0.791). Recovery from hypoxia/anoxia was, however, slightly but significantly weaker in tolbutamide-treated slices than in control slices (F1,137 = 15.539, p < 0.001). We conclude that KATP channels are present in eider duck cerebellar neurons and are activated in hypoxia/anoxia, but that they do not play a key role in the protective shut-down response to hypoxia/anoxia.