Abstract
Summary
Two morphine antagonists, M5050 and naloxone, are equally potent as morphine in blocking peak transient and late steady-state currents in squid axons. Etorphine (M99), a very potent morphinelike analgesic, was no more potent in this preparation than was morphine. The reduction of ionic currents was completely reversible and not accompanied by depolarization of the nerve membrane. The results of these experiments tend to exclude the squid axonal preparation as a good model for studying the analgesic properties of morphine-like compounds. Two interesting findings were (a) naloxone, unlike all the other compounds, significantly shortens the amount of time required for sodium to reach its peak value following a step-depolarization and (b) M99 and M5050 produce a significant potassium inactivation.
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