DIFFERENTIAL-EFFECTS OF CHRONIC ETHANOL EXPOSURE ON ATP-INDUCED 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 1 50 mm ethanol increased [Ca2+]i but did not alter ATP- and BK-induced increases in [Ca2+]i. After a 4-day exposure to 1 50 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 < 0.0 1). 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)-NS,NS,NS',NS'-tetraacetic acid (EGTA) to remove extr acellular free calcium prevented the ATP-induced increase in [Ca2+]i. In contrast, BK produced an increase in [Ca2+], in the presence of exc ess EGTA, suggesting that BK releases calcium from internal stores. Co nsistent with this suggestion, chronic ethanol exposure enhanced BK-in duced phosphoinositide hydrolysis. ATP, however, did not increase phos phoinositide hydrolysis. Pretreatment with 10 muM nifedipine, which bl ocked 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-stim ulated increases in [Ca2+]i and Ca-45(2+) uptake, chronic ethanol expo sure did not alter the depolarization-induced increase in [Ca2+]i or C a-45(2+) uptake. The present study demonstrates that chronic ethanol e xposure inhibits calcium influx through voltage-independent cationic c hannels associated with purinergic receptors and enhances BK-stimulate d phosphoinositide hydrolysis, with a subsequent release of calcium fr om internal stores.