A calcium channel in human submandibular duct cell line, HSG cells, not regulated by P-2U purinergic receptor-mediated intracellular calcium mobilization

Signal transduction via Pt purinergic receptors was investigated in HSG cells, a continuous cell line originally derived from an irradiated human salivary gland. Ligand specificity for nucleotide receptors in HSG cells was investigated with various nucleotides and their analogues. Inositol 1,4,5-trisphosphate (IP3) production was significantly increased by ATP, UTP and ATP gamma S. The ligand specificity of this effect agreed well with that of the P-2U purinergic receptor. On the other hand, Ca-45(2+) influx was stimulated by ATP, UTP > ATP gamma S, ADP, UDP > ADP beta S > AMPPNP, GTP, TTP > CTP, GDP, TDP, AMPPCP, AMPCPP. This ligand specificity of Ca-45(2+) influx was much broader than IP3 production. Also pertussis and cholera toxin had no effect on both IP3 production and Ca-45(2+) influx by ATP or UTP. 3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (Bz-ATP) stimulates Ca-45(2+) influx more effectively than IP3 formation. A 53-kDa membrane protein was photolabelled with [alpha-P-32]Bz-ATP. This 53-kDa protein is a putative P-2 purinergic receptor. In particular, the labelling was inhibited by a ligand profile that corresponded to that for Ca-45(2+) influx. These findings suggest that nucleotides stimulate Ca-45(2+) influx and IP3 formation by separate pathways via pertussis and cholera toxin-insensitive G proteins. Thus, in HSG cells, IP3 formation is coupled to the P-2U subclass, while Ca-45(2+) influx is coupled to another subclass, such as P-2X, that regulates calcium channels. (C) 1997 Elsevier Science Ltd.