Xerostomia is a troublesome complication of diabetes mellitus associated with irreversible damage of salivary glands functioning resulted in the decreased salivation. The most common complications of xerostomia are severe oral dryness, loss of taste acuity, increased incidence of dental caries. Secretion of fluid and electrolyte concentrated saliva is activated by a neurotransmitter acetylcholine (ACh) that induces a complex cytosolic calcium ([Ca2+]cyt) signal required for a synchronized activation of Ca2+-dependent apical Cl− channels and basolateral K+ channels. Previously we showed that diabetes is associated with alterations of ACh-mediated [Ca2+]cyt signaling in submandibular salivary gland (Fedirko et al. 2006), which provides a major contribution to secretion of fluid and electrolytes (Melvin et al. 2005). Since salivation is initiated by an InsP3-mediated calcium release from the endoplasmic reticulum (ER) but subsequently depends on a store-operated calcium entry (SOCE), we hypothesized that both processes could be altered under the diabetes and therefore contribute to the development of xerostomia. Diabetes was induced in male Wistar rats, 21 postnatal days old, by a single i.p. injection of streptozotocin (STZ) dissolved in 100 mM citrate buffer solution (pH 4.25) using 80 mg/kg proportion. Animals were used for experiments 7-8 weeks after the onset of diabetes. The glucose concentration in blood serum was tested in each animal prior to experimentation. Measurements of [Ca2+]cyt were performed using fluorescent Ca2+ dye fura-2/AM. We found that a contribution of mitochondria to the cytosolic calcium clearance in the acinar cells was increased under the diabetes. In particular, we found: i) an increase in the amount of Ca2+ accumulated in the mitochondria in the resting state (by 46±6%, n=19, p<0.05); ii) significantly less pronounced effect of mitochondrial Ca2+ uptake inhibition on the ACh-induced [Ca2+]cyt transients in Ca2+-containing extracellular medium (by 69±11%, n=11, p<0.0001 in diabetic cells versus 29±6%, n=18, p<0.05 in control). We also found that SOCE induced by short ACh stimulation was increased in diabetic acinar cells (by 62±13%, n=16). Inhibition of mitochondrial Ca2+ accumulation equalized SOCE magnitude in the control and diabetic cells indicating the increased role of mitochondria to provide positive feedback on SOCE under diabetes. In contrast, during the sustained cells stimulation (continuous presence of ACh or TG), SOCE was decreased under diabetes (by 43±5%, n=20 and 46±6%, n=8; p<0.05, respectively) suggesting inability of acinar cells to maintain SOCE under potent agonist stimulation. Concluding, our data directly showed severe impairment of the intracellular signaling mechanisms responsible for the activation and maintenance of SOCE. These findings highlight the significant contribution of alteration in mitochondria Ca2+ signaling to the development of xerostomia under the diabetes.