Table 1:

diverse methodologies to measure Ca²⁺ influx via MCU_cx.

	General approach	Central tools	Measures	Remarks	Recent	Related
1	Radioactive mitochondrial Ca2+ uptake measurements	Radiolabeled 45Ca2+	Cell/mitochondria 45Ca2+ retention	Insensitive to pH. Can be conducted over a wide range of [Ca2+] (nM to mM), low temporal resolution, cannot be combined with simultaneous measurements of other signals. Uses either isolated mitochondria or permeabilized cells. Does not quantitatively measure total JMCUcx due to dynamic binding to extramitochondrial buffers.	[4, 11, 17, 80]	[22, 81]
2	Fluorescent measurements of [Ca2+]i	Ca2+-sensitive fluorescent indicators	Change in free extra-mitochondrial [Ca2+]	High temporal resolution can be combined with simultaneous measurements of other signals. Uses either isolated mitochondria or permeabilized cells. Does not quantitatively measure total JMCUcx due to dynamic binding to extram itochondrial buffers.	[5, 11, 14, 16, 18, 26, 67, 74, 82, 83]	[84]
3	Electrophysiological measurements of IMCUcx	Patch-clamping the IMM	Whole-mitoplast or single-channel MCUcx currents	High temporal resolution. Quantitative direct measurements of MCUcx currents. Can be combined with simultaneous measurements of other fluorescent signals. Does not have the sensitivity below [Ca2+] of ~10 μM. Requires mitoplast preparation.	[6, 7, 64]	[85, 86]
4	Fluorescent measurements of total mitochondrial Ca2+ influx via MCUcx	Ca2+-sensitive and voltage-sensitive fluorescent indicators	Total MCUcx Ca2+ flux (JMCUcx), MCUcx conductance (GMCUcx).	High temporal resolution. Quantitatively measure total JMCUcx together with simultaneous quantitative measurements of [Ca2+]i, [Ca2+]m, and ΔΨm. Highly sensitivity below [Ca2+]i of ~10 μM. Carried out in isolated mitochondria but not in permeabilized cells.	[3]	[87], [88, 89]