[Characteristics of inositoltrisphosphate-sensitive Ca2+ stores in the acinar cells of rat submandibular salivary gland].

In the acinar cells of rat submandibular salivary gland activation of cholinoreceptors leads to the release of Ca2+ from endoplasmic reticulum (ER). This Ca2+ release from ER is mainly mediated by InsP3-receptors. In the present work we used Arsenazo III dye and mag-fura 2/AM to measure total cellular calcium content and Ca2+ concentration in the ER ([Ca2+]ER), respectively. We have found that application of InsP3 to the permeabilized acinar cells evoked decrease [Ca2+]ER in dose-dependent manner with EC50 1.3 +/- 0.21 mM. This InsP3-induced Ca2+ release from the ER was potentiated by Ca2+ in the physiological ranges (100-400 nM), modulated by caffeine and ATP. Low concentrations of ATP in (< 1 mM) enhanced the InsP3-induced decrease [Ca2+]ER while high concentrations of ATP markedly suppressed Ca2+ release. Caffeine (2 mM) decreased InsP3-induced Ca2+ release in the presence of Ca2+ however it has no inhibitory effect in the absence of Ca2+. This inhibitory effect of caffeine on InsP3-induced Ca2+ release is overcame by high concentration of InsP3 (20 mM) and ATP (1 mM) indicating that caffeine functionally competes with InsP3 receptor domains. We suggested that the ATP regulation of InsP3-induced Ca2+ release might also play a role in oscillations of intracellular Ca2+ and the maintenance of the cell survival during energy attenuation periods.