We have previously reported that La 3+ inhibited the ATP-induced rise in intracellular Ca 2+ levels ([Ca 2+ ](i)) measured by fura-2 fluorimetry in Madin Darby canine kidney (MDCK) cells. Here we further investigated the ATP-induced Ca 2+ signal. ATP caused a rise in [Ca 2+ ](i) dose-dependently between 1 μM-1 mM. The rises induced by 10 μM-1 mM ATP were inhibited by Ca 2+ removal. The pleateau phase of the ATP response was primarily maintained by Ca 2+ influx because it was reduced or eliminated by Ca 2+ removal. ATP failed to elevate [Ca 2+ ](i) after the endoplasmic reticulum Ca 2+ store had been depleted by 2,5-di-tert-butylhydroquinone or cyclopiazonic acid, suggesting that the ATP-induced Ca 2+ influx was capacitative Ca 2+ entry. Capacitative Ca 2+ entry was directly measured by addition of 5 mM CaCl 2 to cells pretreated with ATP (0.1 mM) in Ca 2+ -free medium. This capacitative Ca 2+ entry was inhibited by econazole (25 μM) or SKF96365 (50 μM). The ATP response was significantly enhanced by extracellular alkalization to pH 8 or pretreatment with gly-phe-β- naphthylamide. Pretreatment with carbonylcyanide m-chlorophenylhydrazone (CCCP) or extracellular Na + removal had no enhancement, implicating that efflux via plasmalemmal Ca 2+ pumps (but not Na + /Ca 2+ exchange) and buffering by lysosomes (but not mitochondria) might be involved in the decay of the ATP response.
|Number of pages||7|
|Journal||Chinese Journal of Physiology|
|Publication status||Published - 1999 Jan 1|
All Science Journal Classification (ASJC) codes
- Physiology (medical)