The two subtypes of phospholipase C-related but catalytically inactive protein (PRIP-1/2) were first identified as novel IP₃-binding proteins. IP₃-induced Ca²⁺ release (IICR) was impaired in cultured cortical neurons from PRIP-1 KO mice while store-operated Ca²⁺ entry (SOCE) was enhanced in hematopoietic B cells in PRIP-2 KO mice. In the present study, we aimed to clarify whether and how Ca²⁺ release from intracellular Ca²⁺ stores and SOCE are different between layer 3 (L3) pyramidal cells (PCs) in PRIP-1/2-DKO and WT mice. The amplitude of Ca²⁺ transients was measured as a difference in the F₃₄₀/F₃₈₀ ratio from the baseline level in L3 PCs in slice preparations incubated with fura-2 AM. A mixed solution of 20 mM K⁺ and 20 mM caffeine induced large Ca²⁺ transients known as Ca²⁺-induced Ca²⁺-release (CICR), which decayed to a plateau level that remained almost constant at least for 10 min examined. The mean peak and plateau amplitudes of Ca²⁺ transients in the PRIP-DKO PCs were significantly larger than those in the WT PCs. Next, whether SOCE occurred following CICR or not was directly examined by reducing [Ca²⁺]_o. The CICR was induced twice consecutively by the first and second applications of the caffeine/high-K⁺ solution, which were separated by 35-40 min. Immediately after the first and second CICR, the caffeine/high-K⁺ solution was changed to the Ca²⁺-free extracellular solution and the standard extracellular solution containing 2 mM Ca²⁺, respectively.