Decrease of calcium conductance induced by opioid agonists has been reported by others for μ-, δ-, and κ-opioid receptors. On the other hand, only μ- and δ-opioid receptors have been reported to increase potassium conductance. Intracellular recordings were made from guinea pig substantia gelatinosa neurons in a brain slice. A subset of cells (29 of 83) were hyperpolarized by the κ-opioid receptor agonist U69593 with an EC50 of 23 nM. The κ-opioid receptor antagonist norbinaltorphimine (10 nM) blocked the hyperpolarization by U69593 but had no effect on the μ-opioid hyperpolarization present in these cells. Naloxone (300 nM) shifted the U69593 dose-response curve to the right, giving an estimated Kd for naloxone of 7.5 and 8.1 nM measured in two cells. The hyperpolarization caused by U69593 was mediated by a potassium conductance as determined with voltage clamp experiments. This demonstrates, depending on the cell type, that all three major opioid receptors (μ, δ, and κ) can increase potassium conductance as well as decrease calcium conductance.
|Original language||English (US)|
|Number of pages||4|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Dec 1 1993|
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