Figure 4.

Increased Ca²⁺ influx following the depletion of extracellular Ca²⁺ in PS1/2 double knockout (PSKO) MEF cells. (A) From this typical recording, PSKO cells showed increased resting [Ca²⁺]_i either in the presence or in the absence of physiological [Ca²⁺]_o compared to wild type PS1/2-transfected (PSWT) cells. Ca²⁺ influx were measured as in Fig. 2C by adding back Ca²⁺ to the extracellular solution as indicated. (B) Ca²⁺ influx were larger in PSKO MEF cells (n = 5) compared to PSWT cells (n = 5). Ca²⁺ influx was measured as in (A). (C) The effects of 2APB on Ca²⁺ influx were compared between PSWT (n = 8) and PSKO MEF cells (n = 8) as described in Fig. 3A. 2APB was able to block larger amount of Ca²⁺ influx from PSKO cells. (D) Steady state levels of PIP₂ in membrane were assayed by using and ELISA kit from PSKO MEF cells (n = 4) and to PSWT MEF cells (n = 4). * represents p < 0.05 from paired t-test.