Interaction between calcium, neutral endopeptidase and the substance P mediated ciliary response in human respiratory...

Following irritation of the airway, the ciliostimulatory effects of the tachykinin, substance P (SP), are thought to be secondary to mucus release. We hypothesized that SP also induces small increases in ciliary beat frequency (CBF) via a calcium-mediated process. Brushed ciliated cells from the nasal epithelium of healthy human subjects were suspended in tissue culture fluid and the acute effects of SP upon these cells were studied in a mucus-free environment. In some preparations, changes in CBF in response to SP were measured with a video-based system. The effect of an SP antagonist, of Ca2+ channel block with verapamil, and of the calcium analogue lanthanum on the SP response were also tested. In other preparations, the ciliated cells were preloaded with Fura-2, a dye which fluoresces with Ca2+ ions, and the response of intracellular Ca2+ to SP was monitored. SP (10(-9)-10(-6) M) transiently increased CBF in a dose-dependent manner, with the maximal response occurring at 10 min. The response was small, with a maximum increase of 8.9%. The SP receptor antagonist (D-pro2,D-trp7,9)-SP (10(-5) M) abolished this effect. Verapamil (10(-5) M) attenuated the response to SP (10(-7) M), whilst lanthanum chloride (250 microM) abolished it. Inhibition of SP destruction by phosphoramidon (10(-6) M) also eliminated the transient rise in CBF. However, compared to SP alone, the combination of SP and phosphoramidon induced a novel delayed lanthanum-sensitive rise in CBF. In other experiments, SP (10(-7) M) induced a transient increase in free intracellular Ca2+ concentration (maximal rise 73%), which returned to baseline before the expected onset of the CBF response. We conclude that substance P induces either a transient or sustained increase in CBF dependent on the rate of destruction of this peptide around tachykinin receptors. These receptors are likely to be linked to lanthanum- and verapamil-sensitive pathways for the entry of Ca2+ into cells. The small magnitude of the rise in CBF makes its physiological role uncertain at present.