The vasoactive peptide urotensin II stimulates spontaneous release from frog motor nerve terminals.
1. The effect of urotensin II (U-II) on spontaneous transmitter release was examined in the frog to see if the biological activity of this vasoactive peptide extended to neural tissues. 2. In normal Ringer solution, frog and human U-II (fU-II and hU-II, respectively) caused concentration-dependent, reversible increases in miniature endplate potential (MEPP) frequency, with hU-II about 22 times more potent than fU-II. hU-II caused a dose-dependent increase in MEPP amplitude, whereas fU-II caused an increase, followed by a decrease with higher concentrations. 3. Increasing extracellular Ca(2+) three-fold had no effect on the MEPP frequency increase to 25 microM hU-II. Pretreatment with thapsigargin to deplete endoplasmic reticulum Ca(2+) caused a 61% reduction in the MEPP frequency increase to 25 microM hU-II. 4. Pretreatment with the phospholipase C inhibitor U-73122 caused a 93% reduction in the MEPP frequency increase to 25 microM hU-II and a 15% reduction in the increase in MEPP amplitude. Pretreating with antibodies against the inositol 1,4,5-trisphosphate (IP(3)) type 1 receptor using liposomal techniques reduced the MEPP frequency increase by 83% but had no effect on MEPP amplitude. 5. Pretreating with protein kinase C inhibitors (bisindolylmaleimide I and III) had no effect on the response to 25 microM hU-II, but pretreating with protein kinase A inhibitors (H-89 and KT5720) reduced the MEPP frequency increase by 88% and completely abolished the increase in MEPP amplitude. 6. Our results show that hU-II is a potent stimulator of spontaneous transmitter release in the frog and that the effect is mediated by IP(3) and cyclic AMP/protein kinase A.
Department of Pharmacology, James H Quillen College of Medicine, East Tennessee State University, PO Box 70577, Johnson City, TN 37614-1708, USA.
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Brailoiu
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Brailoiu
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Miyamoto
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Dun
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000187:drug effects* / Q000378:metabolism; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000378:metabolism; D011894:Rana pipiens; D014579:Urotensins / Q000494:pharmacology* / Q000502:physiology
D004791:Enzyme Inhibitors; D014579:Urotensins; C029677:urotensin II