Effects of ACTH-(1-24) on dopamine and noradrenaline release, B-50 phosphorylation and calmodulin binding to B-50 in vitro.
ACTH-(1-24), 1 microM, enhanced the Ca(2+)-dependent release of [3H]dopamine ([3H]DA) from intact septal synaptosomes by approximately 30%, but had no effect on the release of [3H]noradrenaline ([3H]NA) from intact cortical synaptosomes. Since a strong correlation has been reported between B-50 (phosphorylation) and [3H]NA release from intact or streptolysin-O- (SL-O-) permeated cortical synaptosomes, we investigated whether the effects of ACTH-(1-24) on the release of radiolabelled transmitters are mediated by B-50. We observed that the increment in the release of [3H]DA from SL-O-permeated septal synaptosomes as a result of exposure to a high Ca2+ concentration was much less pronounced than that of the release of [3H]NA from SL-O permeated septal and cortical synaptosomes. ACTH-(1-24) concentration-dependently inhibited [3H]NA release from SL-O-permeated cortical synaptosomes (IC50 value of approximately 10 microM) when ACTH-(1-24) was added 150 s prior to the Ca2+ trigger. Simultaneous addition of ACTH-(1-24), SL-O and Ca(2+)-buffers to cortical synaptosomes did not lead to a change in [3H]NA release at any of the ACTH-(1-24) concentrations tested. ACTH-(1-24) had no effect on B-50 phosphorylation in intact synaptosomes, whereas it concentration-dependently inhibited B-50 phosphorylation in permeated cortical synaptosomes (IC50 value of 100 microM). ACTH-(1-24) inhibited (IC50 value of 10 microM) B-50/calmodulin binding in vitro. We conclude that the effects of high concentrations of ACTH-(1-24) on various biochemical B-50 related parameters are not likely to represent the mechanisms underlying the action of ACTH-(1-24) on neurotransmitter release.
Florijn
W J
WJ
Department of Pharmacology, Rudolf Magnus Institute, Medical Faculty, Utrecht University, The Netherlands.
Hens
J J
JJ
de Graan
P N
PN
Versteeg
D H
DH
Gispen
W H
WH
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D003366:Cosyntropin / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013301:Streptolysins / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium
D001426:Bacterial Proteins; D002147:Calmodulin; D010710:Phosphates; D010761:Phosphorus Radioisotopes; D013301:Streptolysins; C025964:streptolysin O; D014316:Tritium; D003366:Cosyntropin; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D002118:Calcium; D004298:Dopamine; D009638:Norepinephrine