Influence of honokiol on cytosolic calcium concentrations in calcium-free BSS in response to thapsigargin-induced depletion of calcium from the ER and to the subsequent reintroduction of extracellular calcium. CHO-M3 cells were untreated or treated with various concentrations of honokiol, as indicated, for 10 min before measuring calcium content. The cells were switched to a calcium-free BSS 3 min before imaging. Thapsigargin (1 μmol/l) was added at the time indicated by the first arrow. Calcium was added to the extracellular medium (final concentration = 2 mmol/l) at the time indicated by the second arrow. Each line represents the average from four experiments, each with 15-22 cells per measurement.