Localized Ca 2 uncaging reveals polarized distribution of Ca 2 - sensitive Ca 2 release sites : mechanism of unidirectional Ca 2 waves

a 2 -induced Ca 2 release (CICR) plays an important role in the generation of cytosolic Ca 2 signals in many cell types. However, it is inherently difficult to distinguish experimentally between the contributions of messenger-induced Ca 2 release and CICR. We have directly tested the CICR sensitivity of different regions of intact pancreatic acinar cells using local uncaging of caged Ca 2 . In the apical region, local uncaging of Ca 2 was able to trigger a CICR wave, which propagated toward the base. CICR could not be triggered in the basal region, despite the known presence of ryanodine receptors. The triggering of CICR C from the apical region was inhibited by a pharmacological block of ryanodine or inositol trisphosphate receptors, indicating that global signals require coordinated Ca 2