Figure 1

Influence of honokiol on cellular responses to activation of M3 muscarinic receptors. CHO cells expressing the human M3 receptor were loaded with fura-2 to detect changes in cytosolic calcium concentration. The cells were untreated (A) or treated with the indicated concentrations of honokiol for 10 min immediately prior to measuring calcium content (B). A: Control calcium responses to M3 receptor activation. Carbamylcholine (10 μmol/l) was added at the time indicated by the first arrow. This lead to a rapid and sustained increase in cytosolic calcium from 30 to 600-900 nmol/l. Addition of 5 mM EDTA to the medium (second arrow) decreased cytosolic calcium concentration. This is consistent with the interpretation that the sustained increase in calcium concentration following receptor activation is dependent on the influx of extracellular calcium through SOCE channels [12]. Each line represents the response of a single cell from typical experiment repeated over 100 times. B: Honokiol (inset) selectively depresses sustained calcium entry. The initial calcium response to receptor activation (arrow) was largely unaffected by honokiol at concentrations up to 20 μmol/l, but 10 μmol/l honokiol blocked the sustained entry, suggesting a selective blockade of SOCE. At higher concentrations both the initial and sustained responses were depressed. Each line represents the average response of 18-23 cells from a typical experiment; 4 experiments yielded essentially similar results.