Figure 7: SM accumulation in the lysosome reduces TRPML1-mediated Ca²⁺ release.

(a,b) ML-SA1-induced lysosomal Ca²⁺ release was reduced in GCaMP3-ML1-transfected NPA fibroblasts (b) compared with WT fibroblasts (a). (c) Average ML-SA1- (20 μM) and GPN-induced (200 μM) responses in GCaMP3-ML1-transfected WT and NPA fibroblasts. (d) Desipramine (25 μM) treatment for 2–4 h reduced TRPML1-mediated lysosomal Ca²⁺ release responses (20 μM ML-SA1) in GCaMP3-ML1-transfected CHO cells. (e) Pretreatment of a protease inhibitor leupeptin (25 μM) abolished the effects of desipramine in ML-SA1-induced GCaMP3 responses. (f) Summary of the effects of desipramine (25 μM) and fluoxetine (25 μM) treatment for 2–4 h on TRPML1-mediated lysosomal Ca²⁺ release responses (20 μM ML-SA1) in GCaMP3-ML1-transfected CHO cells. (g) Desipramine and fluoxetine treatment for 2–4 h reduced endogenous lysosomal Ca²⁺ release responses (measured with Fura-2 ratios; 100 μM ML-SA1) in CHO cells. For panels c, f and g, the results were averaged for 40–100 cells from at least three independent experiments; data are presented as the mean±s.e.m. Statistical comparisons were made using analysis of variance: *P<0.05.