INTERACTION BETWEEN CALCIUM, NEUTRAL ENDOPEPTIDASE AND THE SUBSTANCE-P MEDIATED CILIARY RESPONSE IN HUMAN RESPIRATORY EPITHELIUM

Following irritation of the airway, the ciliostimulatory effects of th e tachykinin, substance P (SP), are thought to be secondary to mucus r elease, We hypothesized that SP also induces small increases in ciliar y beat frequency (CBF) via a calcium-mediated process. Brushed ciliate d cells from the nasal epithelium of healthy human subjects were suspe nded in tissue culture fluid and the acute effects of SP upon these ce lls were studied in a mucus-free environment, In some preparations, ch anges 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 t ested, In other preparations, the ciliated cells were preloaded with F ura-2, a dye which fluoresces with Ca2+ ions, and the response of intr acellular Ca2+ to SP was monitored. SP (10(-9)-10(-6) M) transiently i ncreased CBF in a dose-dependent manner, with the maximal response occ urring at 10 min, The response was small, with a maximum increase of 8 .9%. The SP receptor antagonist (D-pro(2),D-trp(7,9))-SP (10(-5) M) ab olished this effect, Verapamil (10(-5) M) attenuated the response to S P (10(-7) M), whilst lanthanum chloride (250 mu M) abolished it, Inhib ition of SP destruction by phosphoramidon (10(-6) M) also eliminated t he transient rise in CBF, However, compared to SP alone, the combinati on of SP and phosphoramidon induced a novel delayed lanthanum-sensitiv e 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 respo nse. We conclude that substance P induces either a transient or sustai ned increase in CBF dependent on the rate of destruction of this pepti de around tachykinin receptors. These receptors are likely to be linke d to lanthanum- and verapamil-sensitive pathways for the entry of Ca2 into cells, The small magnitude of the rise in CBF makes its physiolo gical role uncertain at present.