Melatonin biosynthesis in photoreceptor-enriched chick retinal cell cultures: role of cyclic AMP in the K(+)-evoked, Ca(2+)-dependent induction of serotonin N-acetyltransferase activity.
The roles of cyclic AMP and calcium in the regulation of serotonin N-acetyltransferase (NAT) activity were studied in low density monolayer cultures of chick retinal photoreceptors and neurons. Photoreceptor-enriched retinal cell cultures were prepared from embryonic day 6 retinas and cultured for 6 days. NAT activity in these cultures could be induced by treatment with cyclic AMP protagonists, 8Br-cyclic AMP, forskolin, and 3-isobutyl-1-methylxanthine (IBMX), or by treatment with depolarizing concentrations of extracellular K+. The stimulatory effect of K+, which involves Ca2+ influx through dihydropyridine-sensitive channels, was mediated at least in part by cyclic AMP, as indicated by the following observations. Depolarizing concentrations of K+ stimulated the formation of cyclic AMP, and the stimulatory effects of K+ on both cyclic AMP formation and on NAT activity were synergistically potentiated by the cyclic nucleotide phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). MDL 12,330A, a putative adenylate cyclase inhibitor, inhibited K(+)-evoked cyclic AMP accumulation and induction of NAT activity over the identical concentration range. In contrast, MDL 12,300A failed to inhibit the induction of NAT elicited by 8Br-cyclic AMP. H-89, an inhibitor of cyclic AMP-dependent protein kinase, antagonized the induction of NAT activity by either forskolin or K+ with equal potency for both stimuli. These results suggest that cyclic AMP plays an essential role in the induction of NAT activity that occurs as a consequence of membrane depolarization. Cyclic AMP and Ca2+ may also interact at a step distal to adenylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)
Gan
J
J
Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322-3090, USA.
Alonso-Gómez
A L
AL
Avendano
G
G
Johnson
B
B
Iuvone
P M
PM
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000187:drug effects; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D004790:Enzyme Induction; D015640:Ion Channel Gating; D008550:Melatonin / Q000096:biosynthesis*; D008564:Membrane Potentials / Q000502:physiology; D010786:Photoreceptor Cells / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*
D000242:Cyclic AMP; D001191:Arylamine N-Acetyltransferase; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D008550:Melatonin; D011188:Potassium; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine