PHARMACOLOGICAL CHARACTERIZATION OF HETEROLOGOUSLY EXPRESSED ATP-GATED CATION CHANNELS (P-2X PURINOCEPTORS)

cDNAs encoding P-2X purinoceptors from human bladder smooth muscle and from rat PC-12 cells were expressed in oocytes and human embryonic ki dney 293 cells. Agonist potencies of 2-methylthio-ATP = 2-chloro-ATP = ATP greater than or equal to 2'- and 3'-O-(4-benzoylbenzoyl)-ATP grea ter than or equal to adenosine-5'-O-(3-thio)-triphosphate greater than or equal to P-1,P-5-di(adenosine-5') pentaphosphate >> ADP prevailed for both P-2X purinoceptors. There were two main differences in agonis t sensitivity between the two receptors. First, ATP was 10 times more potent at the receptor from bladder (EC(50), 0.8 mu M) than at the rec eptor from PC-12 cells (EC(50), 8.2 mu M). Second, alpha, beta-methyle ne-ATP and L- and D-beta-, gamma-methylene-ATP were agonists in cells expressing the bladder smooth muscle receptor (EC(50), 1-3 mu M) but w ere ineffective in cells expressing the PC-12 receptor. The P-2 purino ceptor antagonists suramin, pyridoxal phosphate 6-azophenyl-2',4'disul fonic acid, and pyridoxal-5-phosphate acted similarly at both receptor forms, producing noncompetitive inhibition, with IC50 values of 1-5 m u M for suramin and pyridoxal phosphate 6-azophenyl-2',4'-disulfonic a cid and 10-20 mu M for pyridoxal-5-phosphate. 4,4'-Diisothiocyanatosti lbene-2,2'-disulfonic acid distinguished receptor subtypes, producing potent inhibition of the bladder smooth muscle P-2X-mediated response, with an IC50 value of 3 mu M; it inhibited the PC-12 form by < 40% at 100 or 300 mu M. This study thus defines the pharmacological properti es of homo-oligomeric forms of these two types of cloned P-2X receptor channels.