Although all Ca²⁺ mobilizing agonists in pancreatic acinar cells utilize the phosphoinositide-signaling (PI) pathway, stimulation by individual agents results in markedly different temporal and spatial patterns of Ca²⁺ signaling. One project is designed to understand at the molecular level how the cell effectively "knows" which PI-coupled agonist it is currently exposed to. Given that tremendous molecular diversity is expressed at all levels of this signaling pathway, our working hypothesis is that individual agonists do not couple to the signaling machinery in an identical fashion. This study involves precisely defining by molecular techniques the individual signaling proteins expressed in the acinar cell and then subsequently assessing if individual agonists utilize discrete and different elements of the PI-signaling pathway. We are utilizing fluorescence imaging techniques including high-speed confocal microscopy to monitor [Ca²⁺]_i while manipulating the signaling pathway with neutralizing antibodies and antisense technology.

A further project relates to the organization and regulation of calcium release sites in exocrine cells. These organelles are defined by the expression of receptors for the second messenger Inositol 1,4,5-trisphosphate. In acinar cells the distribution of these receptors is tightly localized to an area associated with the actin cytoskeleton in the apical secretory pole of the cell. This distribution of receptors is the major factor in defining the spatial characteristics of the Ca²⁺ signal. The nature of the association with the cytoskeleton is being investigated. In addition the regulation of these receptors by phosphorylation and the consequences this may have for Ca²⁺ signaling are also being studied.

Chen, Y., Warner, J.D., Yule, D.I., and Giovannucci, D.R. (2005) Spatiotemporal analysis of exocytosis in mouse parotid acinar cells. Am. J. Physiol. Cell Physiol. 289:C1209-C1219.

Melvin, J.E., Yule, D., Shuttleworth, T.J., and Begenisich, T. (2005) Regulation of fluid and electrolyte secretion in salivary gland acinar cells. Annu. Rev. Physiol. 67:445-469.

Mignen, O., Thompson, J.L., Yule, D.I., and Shuttleworth, T.J. (2005) Agonist activation of arachidonate-regulated Ca²⁺-selective (ARC) channels in murine parotid and pancreatic acinar cells. J. Physiol. 564.3:791-801.

Sneyd, J., Tsaneva-Atanasova, K., Reznikov, V., Bai, Y., Sanderson, M.J., and Yule, D.I. (2006) A method for determining the dependence of calcium oscillations on inositol trisphosphate oscillations. Proc. Natl. Acad. Sci. USA 103:1675-1680.

Wagner II, L.E., Betzenhauser, M.J., and Yule, D.I. (2006) ATP Binding to a uniquesite in the Type-1 S2¯ inositol 1,4,5-trisphosphate receptor defines susceptibility to phosphorylation by protein kinase A. J. Biol. Chem. 281:17410-17419.

Williams, J.A. and Yule, D.I. (2006) Stimulus-secretion coupling in pancreatic acinar cells. In: Physiology of the Gastrointestinal Tract, Fourth Edition, ed. L.R. Johnson, Academic Press.

Won, J.H. and Yule, D.I. (2006) Measurement of Ca²⁺ signaling dynamics in exocrine cells with total internal reflection microscopy. Am. J. Physiol. Gastrointest. Liver Physiol. 291:G146-G155.

Gin, E., Crampin E.J., Brown, D.A., Shuttleworth, T.J., Yule, D.I., and Sneyd, J. (2007) A mathematical model of fluid secretion from a parotid acinar cell. J. Theor. Biol. 248:64-80.

Wagner, L.E., Joseph, S.K., and Yule, D.I. (2008) Regulation of single inositol 1,4,5-triphosphate receptor channel activity by protein kinase A phosphorylation. J. Physiol. 586:3577-3596.

Betzenhauser, M.J., Wagner II, L.E., Iwai, M., Michikawa, T., Mikoshiba, K., and Yule, D.I. (2008) ATP modulation of Ca2+ release by Type-2 and Type-3 inositol (1,4,5)-triphosphate receptors: Differing ATP sensitivities and molecular determinants of action. J. Biol. Chem. 283:21579-21587.