Drosophila neurons respond differently to hypoxia and cyanide than rat neurons

Compared with mammalian species, Drosophila melanogaster exhibits marked tolerance to hypoxia or anoxia. However, the underlying cellular mechanisms of tolerance are still largely unknown. In order to assess the electrophysiologic response to O(2) lack in Drosophila neurons and compare them to those in mammals, we used neurons from embryonic cultures of both Drosophila and rat. We studied the effects of hypoxia on membrane potential V(m), input resistance R(m), rheobase, and action potential characteristics before, during and after 3 to 5 min of hypoxia (measured PO(2)<20 Torr). In Drosophila neurons, on the one hand, V(m) reversibly hyperpolarized with hypoxia by an average of about 20 mV and input resistance decreased by 71% from control. In most cells studied, action potential (AP) amplitude decreased, its duration increased, and its threshold shifted in a hyperpolarized direction before AP generation was attenuated. On the other hand, V(m) in rat cortical neurons reversibly depolarized by an average of 10 mV with hypoxia. Input resistance was reversibly reduced by 58% and, in most cells studied, AP amplitude also decreased and its duration increased. In contrast to the effects of hypoxia on V(m), CN caused a depolarization by 22 mV and a slight increase in R(m) in Drosophila. In the rat, CN was similar to hypoxia in its effect on R(m). We conclude that (1) rat and Drosophila neurons decrease their excitability in hypoxia by activating different mechanisms; (2) the most likely explanation for the hyperpolarization and the decrease in R(m) in Drosophila neurons is the activation of a K(+) conductance; this activation, by itself, cannot explain the results in rat neurons and (3) hypoxia and cyanide have similar effects in rat neurons but are divergent in their effects in Drosophila neurons.