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Journal of Experimental Biology 107,1-8 (1983)
Published by Company of Biologists 1983

Responses of Regularly-Firing Aplysia R₃-R₁₃ Neurones to Normoxia and Hypoxia

PHILIP E. COYER ¹

¹ Department of Neurology and the Neurosciences Program, University of Alabama in Birmingham, Birmingham, Alabama 35294, U.SA.

1. Exposure of 10 R₃-R₁₃ neurones to a 115-min period of hypoxia resulted in depolarization of their membrane potentials (E_M) from a mean of –46.9±3.1 to –20.8±4.4mV (S.E.).

2. Intracellular potassium ion activities (aⁱ_K) decreased significantly from 118.9±5.1 to 67.7±8.5mM-K⁺. This is equivalent to a change in E_K from –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 in aⁱ_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 P_Na/PK ratios were made using a steady-state calculation. Increases in the P_Na/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 aⁱ_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 neuro transmitter and related permeability changes cannot be ruled out as an effect of hypoxia.