Intracellular fluctuations of [Ca2+] are critical for signal transduction in secretory cells. We have recently demonstrated that following ATP stimulation the [Ca2+]G inside mucin granules of goblet cells oscillate. In isolated mucin granules, IP3 stimulation results in similar [Ca2+]G oscillation and oscillatory Ca2+ release to the medium. The oscillation of [Ca2+]G results from a Ca2+/K+ ion exchange process taking place in the polyanionic mucin matrix of the granule. Outflow of Ca2+ to the medium takes place via an IP3-receptor-Ca-channel, and inflow of K+ into the granule takes place via a SKCa -channel present in the granular membrane (Nguyen, Chin & Verdugo, Nature in press). Since pH can strongly modulate the yield of ion-exchange processes in ion-exchange resins and in mucin gels (Katchalsky et al J. Polymer Sci. 7:571,1951; Tam & Verdugo Nature 292:340, 1981), the present experiments were designed to test if pH also oscillates in mucin granules. Isolated mucin granules were loaded with the pH-sensitive probe Lysosensor Green DND-189 (Molecular Probes). Using thin digital optical sectioning techniques (200 nm), we observed that the fluorescence ratio (F/Fi) of Lysosensor Green DND-189 inside mucin granules oscillates. These preliminary results indicate that intragranular pH also undergoes oscillations similar to the Ca2+-oscillations reported by Ca2+-sensitive probes. Thus, pH could play an important role in the modulation of IP3-induced Ca2+-oscillations and release in/from secretory granules.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - Feb 1999|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)