The effect of BayK 8644, a chemical widely used to activate L-type Ca 21 channels, on cytosolic free Ca 21 concentrations ([Ca 21 ] i ) in human oral cancer cells (OC2) has not been explored to date. The present study examined whether BayK 8644 altered basal [Ca 21 ] i levels in suspended OC2 cells by using fura-2. BayK 8644 (10 pM-10 mM) increased [Ca 21 ] i in a concentration-dependent manner. The Ca 21 signal was reduced partly by removing extracellular Ca 21 . BayK 8644-induced Ca 21 influx was blocked by nifedipine, but was not altered by the store-operated Ca 21 entry inhibitors, econazole and SKF96365; protein kinase C modulators phorbol 12-myristate 13-acetate (PMA) and GF109203X; the protein kinase A inhibitor H89; and the phospholipase A 2 inhibitor, aristolochic acid. In Ca 21 -free medium, after pretreatment with 1 mM BayK 8644, 1 mM thapsigargin (an endoplasmic reticulum Ca 21 pump inhibitor)-induced [Ca 21 ] i rises were abolished; and conversely, thapsigargin pretreatment abolished BayK 8644-induced [Ca 21 ] i rises. Inhibition of phospholipase C with U73122 did not change BayK 8644-induced [Ca 21 ] i rises. Collectively, in OC2 cells, BayK 8644 induced [Ca 21 ] i rises by causing phospholipase C-independent Ca 21 release from the endoplasmic reticulum; and Ca 21 influx via L-type Ca 21 channels.