Abstract
Utilizing digital imaging microscopy, the receptor-mediated changes in cytosolic Ca 2+ concentration ([Ca 2+] i) were studied in fura-2-loaded rat parotid acinar cells. The increase in [Ca 2+] i induced by carbachol was initiated in the apical pole of the acinar cells and then spread as a Ca 2+ wave toward the basolateral region. A similar polarization of Ca 2+ signal was observed when the acinar cells were stimulated with substance P or phenylephrine. As the microsomal Ca 2+-ATPase inhibitor thapsigargin did not produce a Ca 2+ wave, activation of phosphoinositide hydrolysis is probably essential to trigger the Ca 2+ wave. Stimulation with 1 μM isoproterenol, a concentration which causes the maximum release of amylase, had no effect on [Ca 2+] i. Extracellular ATP (0.5 mM) induced a homogeneous increase in [Ca 2+] i throughout the cells in the presence of extracellular Ca 2+ but did not change [Ca 2+] i in the absence of extracellular Ca 2+, indicating that the ATP-induced rise in [Ca 2+] i is due to Ca 2+ entry.
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