Opioid peptides with differential affinity for mu and delta receptors decrease sensory neuron calcium-dependent action potentials.

M A Werz; R L Macdonald

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PubMed · 6313900

Opioid peptides with differential affinity for mu and delta receptors decrease sensory neuron calcium-dependent action potentials.

M A Werz·R L Macdonald

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Abstract

Previously, it has been reported that opioid peptides decrease the calcium component of action potentials in a dose-dependent and naloxone-reversible manner consistent with mediation by opiate receptors. To clarify the relation of mu and delta opiate receptors to decreases of somatic calcium-dependent action potential duration, we investigated the potency of two opioid peptides which have different affinities for mu and delta opiate receptors, Leu-enkephalin and morphiceptin. We predicted that Leu-enkephalin would be about 1000-fold more potent than morphiceptin on dorsal root ganglion (DRG) neurons if delta receptors mediated decreases of DRG neuron somatic calcium-dependent action potentials, but that these ligands would be approximately equipotent if mu receptors mediated opiate actions. Additionally, because naloxone has been reported to have a higher affinity for mu receptors in comparison with delta receptors, we investigated agonist sensitivity to naloxone antagonism. When morphiceptin and Leu-enkephalin were tested at equimolar concentrations on individual DRG neurons, a heterogeneous pattern of response to the two opioid peptides was obtained. The response pattern ranged from Leu-enkephalin and morphiceptin producing equal effects to Leu-enkephalin, but not morphiceptin, decreasing action potential duration. DRG neurons that responded only to Leu-enkephalin were approximately 100-fold less sensitive to naloxone antagonism than DRG neurons that responded equally well to both opioid peptides. DRG neurons that responded to both opioid peptides but better to Leu-enkephalin were intermediate in sensitivity to naloxone antagonism. Our results suggest that both mu and delta opiate receptors mediate decreases in somatic calcium-dependent action potentials of DRG neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

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Action Potentials Animals Calcium Cells, Cultured Endorphins Enkephalin, Leucine Ganglia, Spinal In Vitro Techniques Mice Naloxone Neurons, Afferent Receptors, Opioid Receptors, Opioid, delta Receptors, Opioid, mu Time Factors Journal Article Research Support, U.S. Gov't, Non-P.H.S.Research Support, U.S. Gov't, P.H.S.

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M A Werz, R L Macdonald. 1983. Opioid peptides with differential affinity for mu and delta receptors decrease sensory neuron calcium-dependent action potentials.. https://pubmed.ncbi.nlm.nih.gov/6313900/

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