Expression and subcellular localization of the ryanodine receptor in rat pancreatic acinar cells

The ryanodine receptor (RyR) is the principal Ca2+-release channel in excit able cells, whereas the inositol 1,4,5-trisphosphate (InsP(3)) receptor (In sP(3)R) is primarily responsible for Ca2+ release in non-excitable cells, i ncluding epithelia. RyR also is expressed in a number of non-excitable cell types, but is thought to serve as an auxiliary or alternative Ca2+-release pathway in those cells. Here we use reverse transcription PCR to show that a polarized epithelium, the pancreatic acinar cell, expresses the type 2, but not the type 1 or 3, isoform of RyR. We furthermore use immunochemistry to demonstrate that the type 2 RyR is distributed throughout the basolater al and, to a lesser extent, the apical region of the acinar cell, but is ex cluded from the trigger zone, where cytosolic Ca2+ signals originate in thi s cell type. Since propagation of Ca2+ waves in acinar cells is sensitive t o ryanodine, caffeine and Ca2+, these findings suggest that Ca2+ waves in t his cell type result from the co-ordinated release of Ca2+, first from InsP (3)Rs in the trigger zone, then from RyRs elsewhere in the cell. RyR may pl ay a fundamental role in Ca2+ signalling in polarized epithelia, including for Ca2+ signals initiated by InsP(3).