Cyclic AMP modulates but does not mediate the inhibition of [3H]norepinephrine release by activation of alpha-2 adrenergic receptors in cultured rat ganglion cells.
The purpose of this study was to determine whether a decrease in cyclic AMP accumulation mediates the inhibition of norepinephrine release in response to alpha-2 adrenergic receptor activation in cultured rat superior cervical ganglion cells. Superior cervical ganglia from neonatal rats were dissociated and cultured on collagen-coated plastic strips. Neurotransmitter release was assessed by measuring the fractional overflow of tritium in superfused cells prelabeled with [3H]norepinephrine. Intracellular cyclic AMP accumulation was measured using radioimmunoassay. Electrical field stimulation at 1 Hz, 30 pulses, 1 ms duration at 20 min intervals produced an increase in the fractional overflow of tritium that was composed predominantly of intact [3H]norepinephrine. The alpha-2 adrenergic receptor agonist UK-14,304 dose-dependently attenuated the increase in fractional tritium overflow elicited by electrical field stimulation. The adenylyl cyclase activator, forskolin, increased cyclic AMP accumulation in superior cervical ganglion cells and UK-14,304 dose-dependently inhibited forskolin-stimulated cyclic AMP accumulation. UK-14,304 had no effect on basal cyclic AMP accumulation or cyclic AMP accumulation during electrical field stimulation. Forskolin (1-10 microM) or the non-hydrolysable cAMP analog, 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (1-100 microM), slightly increased basal and dose-dependently potentiated the increase in fractional tritium overflow in response to electrical stimulation. Despite enhancement by forskolin and 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate of fractional tritium overflow caused by electrical field stimulation, UK-14304 (1-10 microM) reduced release to a similar degree as that observed in the absence of forskolin or 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate.(ABSTRACT TRUNCATED AT 250 WORDS)
Schwartz
D D
DD
University of Tennessee, Department of Pharmacology, College of Medicine, Memphis 38163.
Malik
K U
KU
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D000068438:Brimonidine Tartrate; D002478:Cells, Cultured; D002854:Chromatography, Paper; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D004558:Electric Stimulation; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000378:metabolism*; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000032:analysis / Q000378:metabolism*; D011810:Quinoxalines / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D013873:Thionucleotides; D005576:Colforsin; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000068438:Brimonidine Tartrate; D000242:Cyclic AMP; D009638:Norepinephrine