Neurones to Normoxia and Hypoxia

1. Exposure of 10 R3-R13 neurones to a 115-min period of hypoxia resulted in depolarization of their membrane potentials (EM) from a mean of -46-9 ± 3-1 to-20-8 ± 4-4mV (S.E.). 2. Intracellular potassium ion activities (a^) decreased significantly from 118-9 ± 5 1 to 67-7 ± 8-5rnM-K. This is equivalent to a change in EKirom — 70-9 mV to —54-5 mV, which is insufficient to account for depolarization of approximately 26 mV. 3. During reoxygenation of the saline surrounding the ganglion, there was a continued depolarization of EM to — 11 • 5 ± 3 • 2 mV and progressive fall ina'K to 49-2 ± 4-9 mM. 4. Decreases in the membrane slope resistance were also observed in these depolarizing neurones. The depression in resistance remained irreversible for as long as experiments were conducted. 5. Computations of PN«/PK ratios were made using a steady-state calculation. Increases in the PN»/PK ratio from 0-030 to 0-045 were observed during hypoxic depolarization using a modification of the Goldman equation which neglects the contribution of chloride ions. Subsequent depolarization and loss of a*K during reoxygenation elevated this value to 0-183. Whether or not the observed depression of the membrane resistance is linked to a change in either the sodium or potassium ion permeability is unknown. Release of neurotransmitter and related permeability changes cannot be ruled out as an effect of hypoxia.