ATP-ACTIVATED NONSELECTIVE CATION CURRENT IN NG108-15 CELLS

ATP (1 mM) induced a biphasic increase in intracellular CA(2+) concent ration ([Ca2+](i)), i.e., an initial transient increase decayed to a l evel of sustained in crease, in NG108-15 cells. The transient increase was inhibited by a phospholipase C inhibitor, 1-[6-[[17 beta-3-methox yestra-1,3,5(10)-trien-17-yl]amino] hexyl]-1H-pyrrole-2,5-dione (U7312 2), whereas the sustained increase was-abolished by removal of externa l Ca2+. We examined the mechanism of the ATP-elicited sustained [Ca2+] (i) increase using the fura-2 fluorescent method and the whole-cell pa tch clamp technique, ATP (1 mM) induced a membrane current with the re versal potential of 12.5 +/- 0.8 mV (n = 10) in Tyrode external soluti on. The EC(50) of ATP was similar to 0.75 mM. The permeability ratio o f various cations carrying this current was Na+ (defined as 1) > Li+ ( 0.92 +/- 0.01; n = 5) > K+ (0.89 +/- 0.03; n = 6) > Rb+ (0.55 +/- 0.02 ; n = 6) > Cs+ (0.51 +/- 0.01; n = 5) > Ca2+ (0.22 +/- 0.03; n = 3) > N-methyl-D-glucamine (0.13 +/- 0.01; n = 5), suggesting that ATP activ ated a nonselective cation current. The ATP-induced current was larger at lower concentrations of external Mg2+. ATP analogues that induced the current were 2-methylthio-ATP (2MeSATP), benzoylbenzoic-ATP, adeno sined 5'-thiotriphosphate (ATP gamma S), and adenosine 5'-O-(2-thiodip hosphate), but not adenosine, ADP, alpha,beta-methylene-ATP (AMPCPP), beta,gamma-methylene-ATP (AMPPCP), or UTP, Concomitant with the curren t data, 2MeSATP and ATP gamma S, but not AMPCPP or AMPPCP, increased t he sustained [Ca2+](i) increase. We conclude that ATP activates a clas s of Ca2+-permeable nonselective cation channels via the P-2z receptor in NG108-15 cells.