The forceresting of the isolated human bronchi was significant decreased by higher concentration BAPTA–AM (100 μM), *, P < 0.05 compared with control. Lower concentration BAPTA–AM (10 μM and 20 μM) reduced IF similar to nominally zero Ca2+- buffer. BAPTA–AM 100 μM vs. 10 μM, # P < 0.05. Data were the mean ± SE. Mean of 4 experiments, with tissue from 4 individuals. Zero Ca2+ buffer or PSS containing 10 μM, 20 μM and 100 μM BAPTA–AM caused a significant fall in PSS buffer basal tone in ASM (P < 0.001 and P < 0.01, respectively, data not shown).