Inhibition by Zn2+ of uridine 5'-triphosphate-induced Ca(2+)-influx but not Ca(2+)-mobilization in rat phaeochromocytoma cells.
1. Uridine 5'-triphosphate (UTP)-evoked increase in intracellular Ca2+ concentration ([Ca]i) and release of dopamine were investigated in rat phaeochromocytoma PC12 cells. UTP (1-100 microM) evoked an increase in [Ca]i in a concentration-dependent manner. This response was decreased to about 30% by extracellular Ca(2+)-depletion, but not abolished. This [Ca]i rise was mimicked by 100 microM ATP but not by 100 microM 2-methyl-thio-ATP or alpha,beta-methylene-ATP in the absence of external Ca2+, suggesting that the response was mediated by P2U purinoceptors, a subclass of P2-purinoceptors. 2. The UTP-evoked [Ca]i rise consisted of two components; a transient and a sustained one. When external Ca2+ was removed, the sustained component was abolished while the transient component was decreased by about 70% but did not disappear. These results suggest that UTP induces Ca(2+)-mobilization and, subsequently, Ca(2+)-influx. 3. The UTP-evoked increase in [Ca]i was not affected by Cd2+ (100 and 300 microM) or nicardipine (30 microM), inhibitors of voltage-gated calcium channels, but was significantly inhibited by Zn2+ (10-300 microM) in the presence of external Ca2+. Zn2+, however, did not affect the Ca2+ response to UTP in the absence of external Ca2+. 4. UTP (30 microM-1 mM) evoked the release of dopamine from the cells in a concentration-dependent manner. This dopamine release was abolished by Ca(2+)-depletion or Zn2+ but not by Cd2+ or nicardipine. 5. Taken together, the data demonstrate that UTP stimulates P2U-purinoceptors and induces a rise in [Ca]i both by Ca(2+)-mobilization and Ca(2+)-influx in PC12 cells. The dopamine release evoked by UTP requires external Ca2+ which may enter the cells through pathways sensitive to Zn2+ but insensitive to Cd2+ or nicardipine.
Koizumi
S
S
Division of Pharmacology, National Institute of Health Sciences, Tokyo, Japan.
Nakazawa
K
K
Inoue
K
K
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000310:Adrenal Gland Neoplasms / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D016257:Fura-2 / Q000737:chemistry; D009529:Nicardipine / Q000494:pharmacology; D016716:PC12 Cells / Q000166:cytology / Q000187:drug effects*; D010673:Pheochromocytoma / Q000378:metabolism*; D051381:Rats; D011983:Receptors, Purinergic / Q000187:drug effects / Q000378:metabolism; D013498:Suramin / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology*; D015032:Zinc / Q000494:pharmacology*
D011983:Receptors, Purinergic; D013873:Thionucleotides; D013498:Suramin; D000255:Adenosine Triphosphate; D009529:Nicardipine; D015032:Zinc; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium; D016257:Fura-2; D014544:Uridine Triphosphate; D004298:Dopamine; C008501:2-methylthio-ATP