Changes in extracellular potassium accumulation produced by opioids and naloxone in frog spinal cord: relation to changes of Na-K pump activity.

Superfusion of the isolated spinal cord of the frog with Ringer solution containing ouabain or naloxone elevated resting [K]e and depolarized the dorsal roots, while the application of enkephalins or morphine decreased [K]e and hyperpolarized the dorsal roots. During repetitive electrical stimulation (10-100 Hz) ouabain and naloxone increased the transient changes of [K]e and enhanced dorsal root potentials. When stimulation stopped, the clearance of K+ was slowed, the poststimulation K+ undershoot disappeared and poststimulation hyperpolarization of dorsal roots was diminished. The opposite effects were found during the application of enkephalins or morphine. Our results imply that the activity of the membrane Na-K pump is reduced after application of naloxone, while opioids enhance it.