Digital imaging of intracellular Ca2+ signaling in rat parotid acinar cells

Utilizing digital imaging microscopy, the receptor-mediated changes in cytosolic Ca2+ concentration ([Ca2+](i)) were studied in fura-2-loaded rat parotid acinar cells. The increase in [Ca2+](i) induced by carbachol was initiated in the apical pole of the acinar cells and then spread as a Ca2+ wave toward the basolateral region. A similar polarization of Ca2+ signal was observed when the acinar cells were stimulated with substance P or phenylephrine. As the microsomal Ca2+-ATPase inhibitor thapsigargin did not produce a Ca2+ wave, activation of phosphoinositide hydrolysis is probably essential to trigger the Ca2+ wave. Stimulation with 1 mu M isoproterenol, a concentration which causes the maximum release of amylase, had no effect on [Ca2+](i). Extracellular ATP (0.5 mM) induced a homogeneous increase in [Ca2+](i) throughout the cells in the presence of extracellular Ca2+ but did not change [Ca]i in the absence of extracellular Ca2+, indicating that the ATP-induced rise in [Ca2+](i) is due to Ca2+ entry.