Fig. 1. JNK inhibitor SP600125 reduces presenilin-1 expression and counteracts ER Ca²⁺ leak. (A) Quantification of mRNA expression levels of presenilin-1 in INS-1 cells treated with different concentrations of the JNK-inhibitor SP600125 or DMSO control for 24 h via qRT-PCR. GAPDH was used as housekeeping gene. Bars indicate mean ± SEM (DMSO Control: n=6; SP600125: n=6). *p<0.05. (B&C) After loading INS-1 cells with the cytosolic Ca²⁺ indicator Fura-2/AM, untreated cells (B) and cells pretreated for 24 h with 100 µM SP600125 (C) were pre-incubated in Ca²⁺-free EGTA containing buffer for either 1 or 20 min. For evaluation of ER Ca²⁺ content, ER Ca²⁺ stores were fully depleted by applying IP₃-generating agonist (100 µM carbachol) together with 15 µM of the SERCA inhibitor BHQ. The maximal ER store depletion was measured as maximal releasable ER Ca²⁺ in the cytosol whereas the ER is considered as fully filled at the one minute time point. Bars on the right represent corresponding statistics, mean ± SEM (B: DMSO Control 1 min: n=164/8; DMSO Control 20 min: n=206/8; C: SP600125 1 min: n=126/6; SP600125 20 min: n=196/8). *p<0.05 tested with unpaired Student's t-test.