An electrophysiological analysis of the effects of morphine on the calcium dependence of neuromuscular transmission in the mouse vas deferens.
1 The effects of morphine on the Ca-dependence of the synaptic potential amplitude in the mouse vas deferens have been determined. 2 The synaptic potential increased with a power factor of 2.4 for [Ca]o between 0.7 mM and 1.8 mM. Morphine (40 nM) decreased the synaptic potential, without altering the second power relationship between the synaptic potential and [Ca]o. 3 Morphine reversed the depression in the synaptic potential which develops during a short high-frequency (10 Hz) train of impulses to facilitation. Consequently the synaptic potential beyond the tenth impulse was unaffected by morphine. 4 Morphine did not alter the facilitation of the synaptic potential which develops during a short low-frequency (less than or equal to 2 Hz) train of impulses in normal [Ca]o. Consequently morphine decreased the synaptic potential for each impulse by about the same percentage amount. 5 Morphine increased the small facilitation in the synaptic potential which occurs during a short low-frequency (less than or equal to 2 Hz) train of impulses in high [Ca]o. This facilitation approximated the predictions based on the assumption that each impulse leaves residual Ca ions bound to receptors involved in transmitter release from the nerve terminal.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009469:Neuromuscular Junction / Q000502:physiology*; D009638:Norepinephrine / Q000378:metabolism; D017981:Receptors, Neurotransmitter / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*; D014649:Vas Deferens / Q000294:innervation / Q000502:physiology
D017981:Receptors, Neurotransmitter; D009020:Morphine; D002118:Calcium; D009638:Norepinephrine