Modulation of Ca2+ oscillations by phosphorylation of Ins(1,4,5)P3 receptors

Abstract

Activation of InsP3Rs (InsP3 receptors) represents the major mechanism underlying intracellular calcium release in non-excitable cells such as hepatocytes and exocrine cells from the pancreas and salivary glands. Modulation of calcium release through InsP3Rs is therefore a major route whereby the temporal and spatial characteristics of calcium waves and oscillations can potentially be ‘shaped’. In this study, the functional consequences of phosphoregulation of InsP3Rs were investigated. Pancreatic and parotid acinar cells express all three types of InsP3R in differing abundance, and all are potential substrates for phosphoregulation. PKA (protein kinase A)-mediated phosphorylation of InsP3Rs in pancreatic acinar cells resulted in slowed kinetics of calcium release following photo-release of InsP3. In contrast, activation of PKA in parotid cells resulted in a marked potentiation of calcium release. In pancreatic acinar cells the predominant InsP3R isoform phosphorylated was the type 3 receptor, while the type 2 receptor was markedly phosphorylated in parotid acinar cells. In order to further decipher the effects of phosphorylation on individual InsP3R subtypes, DT-40 cell lines expressing homotetramers of a single isoform of InsP3R were utilized. These data demonstrate that phosphoregulation of InsP3Rs results in subtype-specific effects and may play a role in the specificity of calcium signals by ‘shaping’ the spatio-temporal profile of the response.