Millisecond analyses of Ca2+ initiation sites evoked by muscarinic receptor stimulation in exocrine acinar cells

High speed laser confocal microscopy (8 ms/image) was applied to the dissoc iated parotid acini as a model to study Ca2+ signaling mechanisms in non-ex citable exocrine secretory cells. Immunofluorescence microscopy showed the localization of IP3 receptor type 2 along the apical membrane region. Musca rinic stimulation with carbachol evoked a rise in [Ca2+](i) that was initia ted from apical region and propagated into basal region as Ca2+ waves. This was most clearly observed when extracellular Ca2+ was omitted. Carbachol a lso triggered the abrupt increase of [Ca2+], simultaneously at both basal a nd apical regions in many acini. Within an acinus, each cell responded sync hronously, The present results suggest that one Ca2+ initiation site in the rat parotid acinar cell is apical region, corresponding to the localizatio n of IF, receptors. Another Ca2+ initiation site is basal region, which see ms to be related to Ca2+ entry from extracellular medium and/or Ca2+ releas e hom basally located organelles such as nuclei and endoplasmic reticulum. (C) 1999 Academic Press.