DIFFERENCES BETWEEN THE ACTIONS OF THIOPENTAL AND PENTOBARBITAL IN SQUID GIANT-AXONS

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  • 1 January 1980
    • journal article
    • research article
    • Vol. 214  (3) , 657-663
Abstract
The action of thiopental and pentobarbital on the giant nerve fiber of the squid Doryteuthis plei under membrane potential control conditions was investigated. The effect of pentobarbital was similar to that reported by other investigators, the replacement of the O2 in C2 by a S atom bestows excitatory properties on the molecule. Thiopental depolarizes the nerve fibers and produces spontaneous repetitive discharges. With concentrations (0.2 mM) of thiopental, the amplitude of the action potential, spontaneous or otherwise, does not change much; but its falling phase is drastically prolonged. Under voltage clamp conditions, it is possible to show that at rest or during activity the thiobarbiturate exhibits a high affinity for K channels. The apparent Kd of pentobarbital on Na and K conductances are, respectively, 1.89 and 0.63 mM, but those of thiopental are 0.52 mM and 32.6 .mu.M. Both barbiturates act as competitive synergists to suppress the increase in Na and the K conductance which occurs during activity.

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