Tryptophan hydroxylase is modulated by L-type calcium channels in the rat pineal gland.
Calcium is an important second messenger in the rat pineal gland, as well as cAMP. They both contribute to melatonin synthesis mediated by the three main enzymes of the melatonin synthesis pathway: tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase. The cytosolic calcium is elevated in pinealocytes following alpha(1)-adrenergic stimulation, through IP(3)-and membrane calcium channels activation. Nifedipine, an L-type calcium channel blocker, reduces melatonin synthesis in rat pineal glands in vitro. With the purpose of investigating the mechanisms involved in melatonin synthesis regulation by the L-type calcium channel, we studied the effects of nifedipine on noradrenergic stimulated cultured rat pineal glands. Tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase activities were quantified by radiometric assays and 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin contents were quantified by HPLC with electrochemical detection. The data showed that calcium influx blockaded by nifedipine caused a decrease in tryptophan hydroxylase activity, but did not change either arylalkylamine N-acetyltransferase or hydroxyindole-O-methyltransferase activities. Moreover, there was a reduction of 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin intracellular content, as well as a reduction of serotonin and melatonin secretion. Thus, it seems that the calcium influx through L-type high voltage-activated calcium channels is essential for the full activation of tryptophan hydroxylase leading to melatonin synthesis in the pineal gland.
Barbosa
Roseli
R
Laboratory of Pharmacology, Butantan Institute, São Paulo, SP, Brazil.
Scialfa
Julieta Helena
JH
Terra
Ilza Mingarini
IM
Cipolla-Neto
José
J
Simonneaux
Valérie
V
Afeche
Solange Castro
SC
D006916:5-Hydroxytryptophan / Q000378:metabolism; D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003563:Cyclic CMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008550:Melatonin / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010870:Pineal Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000031:analogs & derivatives / Q000378:metabolism; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D012701:Serotonin; D003563:Cyclic CMP; C053441:dibutyryl cyclic-3',5'-cytidine monophosphate; D006916:5-Hydroxytryptophan; D014365:Tryptophan Hydroxylase; D000121:Acetylserotonin O-Methyltransferase; D047068:Arylalkylamine N-Acetyltransferase; D009543:Nifedipine; D008550:Melatonin; D007545:Isoproterenol; C006389:N-acetylserotonin; D002118:Calcium; D009638:Norepinephrine