Effects of Morphine on Internally Perfused Squid Giant Axons 1

Abstract

Summary

Morphine, when applied inside the squid axon depressed the action potential within a few minutes, with 10^-3 M resulting in a partial block (30%) and 10^-2 M, a complete block. This block was reversible and not accompanied by depolarization of the resting membrane potential. Voltage clamp experiments revealed that both components of ionic conductances (g_p , g₈₈ ) were equally depressed by morphine, and the curves relating g_p and g₈₈ to the membrane potential were not significantly shifted along the potential axis. These actions of internally applied morphine resemble those reported for local anesthetics. The results of these experiments support the concept that the receptor for morphine is located on the internal surface of the membrane.