Y. Fukushi et al., NA-DEPENDENT RELEASE OF INTRACELLULAR CA2+ INDUCED BY PURINOCEPTORS IN PAROTID ACINAR-CELLS OF THE RAT(), European journal of pharmacology, 336(1), 1997, pp. 89-97
In rat parotid acinar cells, ATP caused a transient increase in the in
tracellular Ca2+ concentration ([Ca2+](i)) in the absence of external
Ca2+. The ATP-induced Ca2+ response was strongly suppressed by removal
of external Na+. The sequence of potency in increasing [Ca2+](i) was
3'-o-(4-benzoyl) benzoyl-ATP > ATP > uridine 5'-triphosphate (UTP). Ad
enosine, AMP, ADP or alpha,beta-metylene ATP did not cause an increase
in [Ca2+](i). The 3'-o-(4-benzoyl) benzoyl-ATP-induced increase in [C
a2+](i) was abolished by removal of external Na+, but the UTP-induced
response was not. The threshold external Na+ concentration required fo
r ATP- or 3'-o-(4-benzoyl) benzoyl-ATP-induced Ca2+ release was 10-20
mM. ATP but not UTP caused a rise in the intracellular Na+ concentrati
on ([Na+](i)). Ca2+ release stimulated by caffeine or treatment with r
yanodine reduced the Ca2+ release evoked by ATP. These results suggest
that ATP, acting through P-2Z purinoceptors, causes Na+ entry by open
ing cation-permeable channels, and thereafter the increase in [Na+](i)
triggers Ca2+ release from ryanodine-sensitive stores. UTP, acting th
rough P-2U purinoceptors, causes Ca2+ release independent of external
Na+. (C) 1997 Elsevier Science B.V.