Effects of bradykinin on intracellular calcium regulation in human ciliated airway epithelium

The Ca2+-mobilizing action of bradykinin (BK) was investigated in ciliated human nasal epithelial (HNE) cells utilizing fura-2 fluorescence and microspectrofluorimetry. In ciliated cells, basal intracellular Ca2+ concentration ([Ca2+](i)) was 123 ± 3 nM (n = 142). BK caused [Ca2+](i) to increase (spike) rapidly (within 6 s) to >550 nM by releasing Ca2+ from intracellular pools. The mean effective dose for the process was 1.5 x 10-7 M BK. The spike was due to the activation of a β2-receptor. The spike was unaffected by inhibitors of either cyclooxygenase or voltage-gated Ca2+ channels. After the spike, [Ca2+](i) decreased to a plateau level (120-250 nM). This plateau persisted (up to 10 min) until the addition of La3+ (0.3 x 10-3 M) or until the removal of either extracellular Ca2+ or the agonist. No changes in adenosine 3',5'-cyclic monophosphate (cAMP) levels were detected after BK exposure. Additional studies revealed that indomethacin (10-6 M), isoproterenol (10-5 M), forskolin (10-5 M), and dibutyryl cAMP (1 mM) had no effect on [Ca2+](i) in ciliated HNE cells. In summary, these data suggest that 1) BK mediates both Ca2+ release from internal pools and Ca2+ entry into the cytoplasm from the extracellular space, and 2) unlike the response to cultured dog airway epithelia, the release of [Ca2+](i) in response to BK does not appear to be mediated by either cyclooxygenase pathway or adenylate cyclase-cAMP systems.