Differential effects of chronic ethanol exposure on ATP- and bradykinin-induced increases in intracellular calcium levels in PC-12 cells.

The present study investigated the regulation of intracellular calcium levels ([Ca2+]i) by ethanol, ATP, and bradykinin (BK) in PC-12 cells. Acute addition of 150 mM ethanol increased [Ca2+]i but did not alter ATP- and BK-induced increases in [Ca2+]i. After a 4-day exposure to 150 mM ethanol, the maximal response to ATP was decreased 39.7 +/- 8.12% (p < 0.01), whereas that to BK was increased 43.8 +/- 6.81% (p < 0.01). There was no change in the EC50 values for either ATP or BK after chronic ethanol exposure. Addition of excess ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) to remove extracellular free calcium prevented the ATP-induced increase in [Ca2+]i. In contrast, BK produced an increase in [Ca2+]i in the presence of excess EGTA, suggesting that BK releases calcium from internal stores. Consistent with this suggestion, chronic ethanol exposure enhanced BK-induced phosphoinositide hydrolysis. ATP, however, did not increase phosphoinositide hydrolysis. Pretreatment with 10 microM nifedipine, which blocked depolarization-evoked increases in [Ca2+]i, reduced ATP- and BK-induced increases in [Ca2+]i but did not alter the response to chronic ethanol exposure. Although acute addition of ethanol reduced KCl-stimulated increases in [Ca2+]i and 45Ca2+ uptake, chronic ethanol exposure did not alter the depolarization-induced increase in [Ca2+]i or 45Ca2+ uptake. The present study demonstrates that chronic ethanol exposure inhibits calcium influx through voltage-independent cationic channels associated with purinergic receptors and enhances BK-stimulated phosphoinositide hydrolysis, with a subsequent release of calcium from internal stores.