Reversible changes in the intracellular potassium ion activities and membrane potentials of Aplysia L2-L6 neurones in response to normoxia and hypoxia.

1. Exposure of 7 L2-L6 neurones to hypoxia for 65 min resulted in hyperpolarization of the membrane potential (EM) from a mean of -49.1 +/- 2.1 to -54.1 +/- 3.6 mV (S.E.). 2. Intracellular potassium ion activities (aiK) increased significantly from 137.7 +/- 4.0 to 155.6 +/- 3.4 mM-K+. This is equivalent to a change in EK from -74.2 mV commensurate with the observed hyperpolarization of 5 mV. 3. The reversibility of these responses was noted by reoxygenating the solution surrounding the ganglion for a period of 55 min. 4. In another group (n = 7) of L2-L6 neurones, the responses in aiK, EM, and EK were slower, although following hypoxia for 90-110 min, similar changes in the levels of these membrane phenomena were recorded. 5. PNa/PK ratios were computed for both L2-L6 groups of neurones using a modified version of the Goldman equation. There were only slight decreases in this ratio with hypoxia, which were not significantly different from the control (normoxia). Therefore, we conclude that this period of hypoxia is capable of stimulating the sodium pump of these cells since the membrane potentials seem to hyperpolarize according to the increase in aiK. However, tonic release of neurotransmitter, which could hyperpolarize these neurones and attract intracellular potassium, cannot be ruled out as an effect of hypoxia.