AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 3 540-R545, Copyright © 1991 by American Physiological Society
Conduction blockade in myelinated fibers by gaseous and volatile substances
F. G. Carpenter
Department of Pharmacology, University of Alabama, Birmingham 35294.
The minimum ambient partial pressure required to reversibly disrupt
conducted responses in myelinated nerve fibers (Pblock) was determined for
11 gases and chloroform. For all but one substance, Pblock was inversely
proportional to their nonaqueous solubility; large-diameter fibers were
less vulnerable than fibers of small diameter. No "anesthetic" effect was
displayed by SF6. At the Pblock for three of the agents, the time for
completion of their anesthetic action (tb) was proportional to their
lipid-to-aqueous solubility ratio. When the ratio was large, tb was longer
than when the ratio was small; blockade became complete after the partial
pressure of the agent in the lipid or nonaqueous phase of the axon membrane
became equal to Pblock. The access of these substances to an nonaqueous
site was neither pH nor frequency dependent, but in the case of SF6 access
did appear to be limited by its molal volume.
