Store‐Operated Ca 2+ Entry in Oocytes Modulate the Dynamics of IP 3 ‐Dependent Ca 2+ Release From Oscillatory to Tonic

Ca 2+ signaling is ubiquitous and mediates various cellular functions encoded in its spatial, temporal, and amplitude features. Here, we investigate the role of store‐operated Ca 2+ entry (SOCE) in regulating the temporal dynamics of Ca 2+ signals in Xenopus oocytes, which can be either oscillatory or tonic. Oscillatory Ca 2+ release from intracellular stores is typically observed at physiological agonist concentration. When Ca 2+ release leads to Ca 2+ store depletion, this triggers the activation of SOCE that translates into a low‐amplitude tonic Ca 2+ signal. SOCE has also been implicated in fueling Ca 2+ oscillations when activated at low levels. Here, we show that sustained SOCE activation in the presence of IP 3 to gate IP 3 receptors (IP 3 R) results in a pump‐leak steady state across the endoplasmic reticulum (ER) membrane that inhibits Ca 2+ oscillations and produces a tonic Ca 2+ signal. Tonic signaling downstream of SOCE activation relies on focal Ca 2+ entry through SOCE ER‐plasma membrane (PM) junctions, Ca 2+ uptake into the ER, followed by release through open IP 3 Rs at distant sites, a process we refer to as “Ca 2+ teleporting.” Therefore, sustained SOCE activation in the presence of an IP 3 ‐dependent “leak” pathway at the ER membrane results in a switch from oscillatory to tonic Ca 2+ signaling. J. Cell. Physiol. 232: 1095–1103, 2017. © 2016 Wiley Periodicals, Inc.