Synthesis and release of acetylcholine by the isolated perifused trout caudal neurosecretory system.
The neurons of the caudal neurosecretory system of teleosts contain, in addition to urotensin I and urotensin II, a high concentration of acetylcholine (T. Ichikawa, 1978, Gen. Comp. Endocrinol. 35, 226-233). The isolated urophysis (and attached terminal spinal cord region) of the rainbow trout Oncorhynchus mykiss was incubated with [3H]choline (0.2 MBq/ml) for 45 min at 22 degrees in the presence of the cholinesterase inhibitor, physostigmine. Unreacted choline was removed by perifusion with fish Ringer solution. Incorporation of radioactivity into newly synthesized [3H]acetylcholine was 4.9 +/- 2.1 x 10(5) Bq/g wet tissue wt. When incubations were carried out in the presence of hemicholinium-3, an inhibitor of high-affinity choline uptake, or when physostigmine was omitted from the incubation buffer and/or when [3H]inulin was substituted for [3H]choline, the incorporation of radioactivity was greatly reduced (< 0.5 x 10(5) Bq/g). The release of [3H]acetylcholine from the preparation increased to 338 +/- 59% of basal (P < 0.05) when the concentration of K+ in the perifusion buffer was raised to 41 mM, but neither urotensin I (10(-7) M) nor urotensin II (10(-6) M) had a significant effect on release. The data indicate that the trout caudal neurosecretory system possesses a high-affinity uptake system for choline and that newly synthesized acetylcholine is released in response to a depolarizing stimulus.
Conlon
J M
JM
Regulatory Peptide Center, Creighton University School of Medicine, Omaha, Nebraska 68178, USA.
Balment
R J
RJ
D000109:Acetylcholine / Q000096:biosynthesis / Q000378:metabolism*; D000818:Animals; D002794:Choline / Q000378:metabolism; D018678:Cholinergic Agents / Q000494:pharmacology; D006426:Hemicholinium 3 / Q000494:pharmacology; D066298:In Vitro Techniques; D009490:Neurosecretory Systems / Q000187:drug effects / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D010477:Perfusion; D014579:Urotensins / Q000096:biosynthesis
D018678:Cholinergic Agents; D014579:Urotensins; D006426:Hemicholinium 3; C029676:urotensin I; C029677:urotensin II; D002794:Choline; D000109:Acetylcholine