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1 Pharmacology and Physiology, University of Rochester, Rochester, New York, United States
2 Department of Imaging Sciences, Institute of Optics, University of Rochester, Rochester, New York, United States
* To whom correspondence should be addressed. E-mail: david_yule{at}urmc.rochester.edu.
[Ca2+]i signals are central to the mechanisms underlying fluid and protein secretion in pancreatic and parotid acinar cells. Calcium release was studied in natively buffered cells following focal laser photolysis of caged molecules. Focal photolysis of caged-InsP3 in the apical region resulted in Ca2+ release from the apical trigger zone and after a latent period the initiation of an apical to basal Ca2+ wave. The latency was longer and the wave speed significantly slower in pancreatic compared to parotid cells. Focal photolysis in basal regions evoked only limited Ca2+ release at the photolysis site and never resulted in a propagating wave. Instead, an apical to basal wave was initiated following a latent period. Again, the latent period was significantly longer under all conditions in pancreas than parotid. Although slower in pancreas than parotid, once initiated, the apical to basal wave speed was constant in a particular cell type. Photo-release of caged-Ca2+ failed to evoke a propagating Ca2+ wave in either cell type. However, the kinetics of the Ca2+ signal evoked following photolysis of caged-InsP3 were significantly dampened by ryanodine in parotid but not pancreas, indicating a more prominent functional role for RyR following InsP3R activation. These data suggest that differing expression levels of InsP3R, RyR and possibly cellular buffering capacity may contribute to the fast kinetics of Ca2+ signals in parotid when compared to pancreas. These properties may represent a specialization of the cell type to effectively stimulate Ca2+-dependent effectors important for the differing primary physiological role of each gland.
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