Imaging of intracellular Ca2+ waves induced by muscarinic receptor stimulation in rat parotid acinar cells.
Changes in cytosolic Ca2+ concentration ([Ca2+]i) following muscarinic receptor stimulation were studied with digital imaging microscopy in small clusters of Fura-2 loaded rat parotid acinar cells. In the absence of extracellular Ca2+, the increase in [Ca2+]i evoked by a high concentration (10 microM) of carbachol (CCh) was initiated in the apical pole of the acinar cells about 0.4 s after stimulation and then rapidly spread as a Ca2+ wave toward the basolateral region. The [Ca2+]i reached the maximum high level throughout the cells 1-2 s after stimulation. As Ca2+ was eliminated from the extracellular medium, the Ca2+ wave was a result of Ca2+ release from intracellular stores. The magnitude and velocity of the Ca2+ wave decreased with decreasing concentration of CCh, and the increase in [Ca2+]i induced by low CCh concentrations (< or = 0.5 microM) was always larger in the apical region of acinar cells than in the basal region. The Ca2+ wave was also observed in isolated single acinar cells, indicating that the maintenance of acinar structure is not essential for the development of the Ca2+ wave. Thapsigargin (ThG), an inhibitor of the endoplasmic reticulum Ca2+ pump, caused a slow and homogeneous increase in [Ca2+]i throughout the cells. Addition of ThG after CCh, or addition of CCh after ThG, did not stimulate further increases in [Ca2+]i, suggesting that the inositol-1,4,5-trisphosphate (InsP3) and ThG-sensitive Ca2+ stores overlap in parotid acinar cells. The present study supports the hypothesis that formation of InsP3 is essential to trigger the Ca2+ wave and that the development of the Ca2+ wave may be attributed to regional differences in InsP3 sensitivity of Ca2+ stores. The agonist-induced Ca2+ wave is probably a general phenomenon in exocrine acinar cells.
Tojyo
Y
Y
Department of Dental Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan. tojyo@hucc.hokudai.ac.jp
Tanimura
A
A
Matsumoto
Y
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002217:Carbachol / Q000378:metabolism / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism; D018721:Muscarinic Agonists / Q000378:metabolism / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D000252:Calcium-Transporting ATPases; D002118:Calcium