(A) Records of membrane current (above) and electrical membrane capacitance (below) during the Standard MEND protocol in BHK fibroblasts expressing cardiac Na/Ca exchangers (NCX1). Cells are opened in Ca-free extracellular solution with 0.5 mM EGTA, using a cytoplasmic (pipette) solution containing 40 mM cytoplasmic Na, 8 mM MgATP and 0.2 mM GTP. Thereafter, Ca influx via Na/Ca exchange is activated by extracellular application of 3 mM Ca for 10 s. During Ca influx, outward membrane current reflects 3Na/1 Ca exchange. Membrane area (i.e., Cm) increases by 30% as a result of exocytosis (i.e., fusion of vesicles to the cell surface). After terminating Ca influx, membrane area is stable for nearly 60 s and then declines over 2 min by 70% as plasmalemma is internalized via endocytosis. (B) Composite results implicating a role for mitochondria in the initiation of MEND. From left to right, bar graphs give results for Standard MEND (CTR, black and white), Standard MEND without cytoplasmic Pi (purple), with the mitochondrial Ca uptake inhibitor, RU323 (20 μM, blue), with the PTP blockers, cyclosporine A (5 μM, green) and NIM811 (2 μM, orange), after PKC activation by OAG (15 μM, yellow), and after rapid perfusion of a mitochondrial uncoupler, CCCP (20 μM) with an ATP synthetase inhibitor, oligomycin (OM, 5 μM, red). n > 6 in all panels. MEND was quantified as fractional decrease of Cm from point 2 to point 3, and stars indicating significance have their usual meanings.