1. Effect of Brefeldin A on Melatonin Secretion of Chick Pineal Cells
- Author
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Yoshitaka Fukada, Takaoki Kasahara, Masayuki Murata, Toshiyuki Okano, Tsuyoshi Hirota, and Satoshi Kagiwada
- Subjects
endocrine system ,medicine.medical_specialty ,Arylamine N-Acetyltransferase ,Circadian clock ,Golgi Apparatus ,Pineal Gland ,Biochemistry ,Pinealocyte ,Melatonin ,Pineal gland ,symbols.namesake ,chemistry.chemical_compound ,Internal medicine ,medicine ,Animals ,Secretion ,RNA, Messenger ,Circadian rhythm ,Molecular Biology ,Cells, Cultured ,Protein Synthesis Inhibitors ,Brefeldin A ,Chemistry ,General Medicine ,Golgi apparatus ,Circadian Rhythm ,medicine.anatomical_structure ,Endocrinology ,symbols ,Chickens ,hormones, hormone substitutes, and hormone antagonists ,medicine.drug - Abstract
Melatonin is secreted from the pineal gland in a circadian manner. It is well established that the synthesis of melatonin shows a diurnal rhythm reflecting a daily change in serotonin N-acetyltransferase (NAT) activity, and the overall secretion of melatonin requires a cellular release process, which is poorly understood. To investigate the possible involvement of Golgi-derived vesicles in the release, we examined the effect of brefeldin A (BFA), a reversible inhibitor of Golgi-mediated secretion, on melatonin secretion of cultured chick pineal cells. We show here that treatment with BFA completely disassembles the Golgi apparatus and reduces melatonin secretion. In more detailed time course experiments, however, the inhibition of melatonin secretion is only observed after the removal of BFA in parallel with the reassembly of the Golgi apparatus. This inhibition of melatonin secretion is not accompanied by accumulation of melatonin in the cells. These observations indicate that chick pineal melatonin is released independently of the Golgi-derived vesicles, and suggest inhibition of melatonin synthesis after the removal of BFA. By measuring the activities and mRNA levels of melatonin-synthesizing enzymes, we found that the removal of BFA specifically inhibits NAT activity at the protein level. On the other hand, BFA causes no detectable phase-shift of the chick pineal oscillator regulating the circadian rhythm of melatonin secretion. The results presented here suggest that the Golgi-mediated vesicular transport is involved in neither the melatonin release nor the time-keeping mechanism of the circadian oscillator, but rather contributes to the regulation of NAT activity.
- Published
- 2001