Histamine stimulates a biphasic calcium response in the human tracheal epithelial cell line CF/T43

We have studied the cytosolic free Ca2+ concentration ([Ca2+]i) response to histamine and other inflammatory mediators in a cystic fibrosis tracheal epithelial cell line (CF/T43) using digital fluorescence imaging. Brief pulses of histamine increased [Ca2+]i in a concentration-dependent manner with threshold, half-maximal, and maximal responses at approximately 5 microM, 120 microM, and 10 mM, respectively. The calcium response to sustained histamine exposure was markedly biphasic, consisting of an early peak (to approximately 2.4 microM [Ca2+]i) followed by a smaller second peak that lasted 45-60 s. Neither peak was directly dependent on Ca2+ influx. In contrast, stimulation with bradykinin gave a single peak followed by a smooth decay back to baseline levels. Sustained perfusion with histamine did not affect the bradykinin response, which is known to be mediated by inositol 1,4,5-trisphosphate (IP3). The H1-type histamine receptor blockers mepyramine, diphenhydramine, and (+)-chlorpheniramine were potent antagonists of the histamine response. Diphenhydramine was also a weak agonist at high concentrations (> or = 1 mM) and gave a biphasic response similar to that with histamine. The H2-type receptor blocker cimetidine and the H3-type receptor blocker thioperamide had no effect. Indomethacin failed to inhibit the second phase of the histamine-stimulated [Ca2+]i response, suggesting that the second [Ca2+]i peak is not due to secondary production of prostaglandins. Neomycin, which inhibits IP3 production, completely abolished the [Ca2+]i response to bradykinin stimulation but did not affect the second phase of the histamine response. The biphasic nature of the histamine response, the insensitivity of the second [Ca2+]i peak to neomycin, and the independence of bradykinin and histamine responses suggest that histamine may modulate [Ca2+]i through multiple IP3 and non-IP3 pathways.