Ryanodine receptor expression is associated with intracellular Ca2+ release in rat parotid acinar cells

1 Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York 14214; and 2 Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120 The ryanodine receptor mediates intracellular Ca 2+ mobilization in muscle and nerve, but its physiological role in nonexcitable cells is less well defined. Like adenosine 3',5'-cyclic monophosphate and inositol 1,4,5-trisphosphate, cyclic ADP-ribose (0.3-5 µM) and ADP (1-25 µM) produced a concentration-dependent rise in cytosolic Ca 2+ in permeabilized rat parotid acinar cells. Adenosine and AMP were less effective. Ryanodine markedly depressed the Ca 2+ -mobilizing action of the adenine nucleotides and forskolin in permeabilized cells and was likewise effective in depressing the action of forskolin in intact cells. Cyclic ADP-ribose-evoked Ca 2+ release was enhanced by calmodulin and depressed by W-7, a calmodulin inhibitor. A fluorescently labeled ligand, 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3,4-diaza-s-indacene-3-propionic acid-glycyl ryanodine, was synthesized to detect the expression and distribution of ryanodine receptors. In addition, ryanodine receptor expression was detected in rat parotid cells with a sequence highly homologous to a rat skeletal muscle type 1 and a novel brain type 1 ryanodine receptor. These findings demonstrate the presence of a ryanodine-sensitive intracellular Ca 2+ store in rat parotid cells that shares many of the characteristics of stores in muscle and nerve and may mediate Ca 2+ -induced Ca 2+ release or a modified form of this process. cyclic adenosine diphosphate-ribose; adenosine 3',5'-cyclic monophosphate