Pharmacological evidence suggests the presence of IP, insensitive stores in exocrine cells that are sensitive to the ryanodine receptor (RyR)/Ca2+ release channel ligand, caffeine (Wakui et al. 1990. Cell 63:1025). In the present study, we have identified a RyR in mouse parotid acinar cells using membrane receptor binding analysis. Binding of [3H] ryanodine (Ry) was Ca2+, salt, pH, and temperature dependent. [3H]Ry bound specifically to membranes with high affinity (6 nM); receptor density equaled 275 fmol/mg protein. Caffeine and ATP, activators of Ry binding, were less effective than the inhibitors Mg2+ and ruthenium red. 4-CI-3-ethylphenol markedly enhanced Ry binding consistent with its Ca2+ release effect in non-excitable cells. A putative endogenous ligand of RyR/Ca2+ release channel, cADPR (10 nM-10 μM), was found not to effect Ry binding; at 2.5 μM cADPR, binding of Ry did not differ from control over a broad range of free [Ca2+]. Bastadin, a novel modulator of skeletal FK506 binding protein (FKBP12)/RyR complex, increased Ry binding 3-4 fold. The immunosuppressant FK506, in addition to enhancing Ry binding alone, antagonized the action of bastadin suggesting that an imrnunophilin modulates receptor binding of Ry. These findings of specific Ry binding and the actions of known modulators support the presence of a RyR in acinar cells of the parotid, and suggest an alternative mechanism for Ca2+ release from intracellular stores to the cytosol during regulated secretion.
|Original language||English (US)|
|State||Published - 1996|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology