Figure 1. NCLX is responsible for NCX_mit in HL-1 cardiomyocytes.

(a) Mitochondria (TagRFP-mito, red) and SR (Cameleon D1ER, green) were localized close together. A merged image is shown on the right with plasma membrane stained by di-8-ANEPPS (blue). nuc: nucleus. (b) mNCLX labelled with TagGFP2 (green) and mitochondria (TagRFP-mito, red) were co-localized. The nucleus was stained by Hoechst 33342 (blue) and the merged image is shown on the right. (c) Expression of mNCLX protein was reduced in mNCLX siRNA-transfected cells. β-actin was used as a reference. con; control siRNA. NCLX KD; mNCLX siRNA. (d), (e) NCX_mit activity was measured in cells transfected with control siRNA (control siRNA; white), mNCLX siRNA (mNCLX siRNA; red) and mNCLX siRNA with hNCLX plasmid (mNCLX siRNA & hNCLX; green). Initial velocity of Ca²⁺_mit decay was significantly decreased by knocking down NCLX but recovered by co-expressing hNCLX with mNCLX siRNA (N = 4–6). * P < 0.05, ** P < 0.01.