Concentration-dependent effect of UDP on ISC and [Ca2+]i.

(A) Epithelia were initially bathed in normal K-H solution while changes in ISC were recorded. A serosal-to-mucosal-directed Cl gradient was applied across the monolayers by changing the apical K-H solution to one with reduced Cl concentration to facilitate Cl secretion (not shown). Different concentrations of UDP were added to the apical side as indicated. Data presented are representative of at least four independent experiments. (B) UDP-evoked increases in [Ca2+]i were monitored by a microfluorimetric technique using the calcium-sensitive fluorescent dye Fura-2. Cells grown on glass coverslips were initially superfused with normal K-H solution. The K-H solution was then changed to a nominally Ca2+-free K-H solution, and the cells were stimulated with different concentrations of UDP as indicated. Data presented are representative of at least four independent experiments. (C) Concentration-response relationship for the effect of UDP upon ΔISC in 16HBE14o- epithelia. The changes in ISC for the first and second peaks were quantified and plotted against the concentration of UDP used. Each data point represents the mean ± S.E. (n = 4–5). (D) Concentration-response relationship for the effect of UDP upon changes in [Ca2+]i represented by Δratio. Each data point represents the mean ± S.E. (n = 4–5). (E) Application of CysLT1 receptor agonists (10 µM), LTC4 or LTD4, did not cause any discernible increase in ISC and did not affect the subsequent 100-µM UDP-evoked ISC responses. Data presented are representative of at least four independent experiments.

Keyword(s)

udp

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