Action potentials in single axons: Effects of hyperbaric air and hydrostatic pressure

Resting potential and action potential parameters of crayfish (Procambarus acutus) single axon were examined under hyperbaric air and hydrostatic pressure to 8.6 atmospheres absolute to determine if evidence for the basis of neurological dysfunctions that may occur in diving in this pressure range is detectable at the membrane level. Hyperbaric air increased the maximum rates of depolarization and repolarization of the action potential (2.2 ± 0.2) and (2.1 ± 0.2)%/atm, respectively. Hydrostatic pressure had an opposite effect, decreasing the maximum rates of depolarization and repolarization by (0.57 ± 0.13) and (0.9 ± 0.3)%/atm, respectively. Action potential duration was decreased (0.91 ± 0.19)%/atm by hyperbaric air. Action potential amplitude, resting potential, and threshold were unchanged by increasing pressure. Increasing the nitrogen tension alone produced results consistent with hyperbaric air compression. Thus, increased hydrostatic and nitrogen pressure oppositely affect the rates of polarization of the action potential in a reversible manner at pressures in the range encountered by human divers.