Figure 3. Sequential CPA application reveals an inverse relationship between global [Ca²⁺]_i and store refilling.

Time courses of [Ca²⁺]_i changes recorded from two individual cells in a typical experiment. Extracellular Ca²⁺ was omitted as indicated and then CPA (30 μM) was applied in Ca²⁺-free extracellular solution from 10 min. Following the first CPA application, a modified Tyrode solution containing 2 mM Ca²⁺ was re-applied a second time. Brackets indicate areas under which [Ca²⁺]_i were integrated to estimate store content during sequential CPA application (CPA₁ and CPA₂) and global [Ca²⁺]_i elevation during Ca²⁺ readdition ([Ca²⁺]_SOCE). Values of [Ca²⁺]_i prior to the CPA or extracellular Ca²⁺ readdition were subtracted before integration. Note that application of ionomycin (Iono, 1 μM) following the second CPA application in both cells generates only a small elevation in [Ca²⁺]_i.