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 dissociated parotid acini as a model to study Ca2+ signaling mechanisms in non-excitable exocrine secretory cells. Immunofluorescence microscopy showed the localization of IP3 receptor type 2 along the apical membrane region. Muscarinic stimulation with carbachol evoked a rise in [Ca2+]i that was initiated from apical region and propagated into basal region as Ca2+ waves. This was most clearly observed when extracellular Ca2+ was omitted. Carbachol also triggered the abrupt increase of [Ca2+]i simultaneously at both basal and apical regions in many acini. Within an acinus, each cell responded synchronously. The present results suggest that one Ca2+ initiation site in the rat parotid acinar cell is apical region, corresponding to the localization of IP3 receptors. Another Ca2+ initiation site is basal region, which seems to be related to Ca2+ entry from extracellular medium and/or Ca2+ release from basally located organelles such as nuclei and endoplasmic reticulum.
Takemura
H
H
Department of Pharmacology, Sapporo Medical University, South 1, West 17, Sapporo, 060-8556, USA. takemura@saped.ac.jp
Yamashina
S
S
Segawa
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D008297:Male; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D000442:Octanols / Q000494:pharmacology; D010306:Parotid Gland / Q000033:anatomy & histology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors
D000442:Octanols; D011976:Receptors, Muscarinic; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium