UTP activates phospholipase C-Ca2+ system through a receptor different from the 53-kDa ATP receptor in PC12 cells

Extracellular ATP (a purine nucleotide) and UTP (a pyrimidine nucleotide) both activated phospholipase C with a similar potency and efficacy; however, in contrast to ATP which induced a remarkable norepinephrine release, UTP-induced norepinephrine release was small in PC12 cells, a rat pheochromocytoma cell line. ATP, its derivatives (2-methylthioadenosine 5'-triphosphate (MeSATP) and 2'- and 3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP)) and UTP increased intracellular Ca2+ in the presence of 2 mM extracellular Ca2+ with the potency order of ATP > MeSATP > BzATP = UTP. Under the low extracellular Ca2+ conditions, the Ca2+ response to purine nucleotides was markedly reduced, but the UTP response was not. The [32P]BzATP labeling of a 53-kDa putative ATP receptor coupled to a channel system (Majid, M.A., Okajima, F., and Kondo, Y. (1992) Biochim. Biophys. Acta 1136, 283-289) was markedly inhibited by ATP, but not by UTP. These results suggest that UTP activates the phospholipase C-Ca2+ system through a receptor different from the 53-kDa ATP receptor.