Table 1.

In vitro properties of the selected biosensors.

Biosensor	FRET Pair	Troponin C	Linkers	ΔR/R In Vitro (%)	ΔR/R Ex Vivo (%)	Kd (µM)	Decay Time (s)	Hill Slope
Twitch-1	ECFP cpCit174	Opsanus tau swim bladder and white muscle	P, P	400		0.25	0.8	1.18
Twitch-2B	mCerulean3 cpVenusCD	Opsanus tau swim bladder and white muscle	VADA, PIYP	800	26.5 †	0.2	2.8	1.31
Twitch-4	ECFP cpCit174	Opsanus tau swim bladder and white muscle	DA, PIY	600		2.8	0.5	1.04
TN-XXL *	ECFP cpCit174	Chicken skeletal muscle	RML, EL	260	10 ‡	0.8	0.88	1.5

* TN-XXL data from [33]. The Kd was obtained in vitro and the decay time in a preparation of neuromuscular junction of Drosophila melanogaster. ^† Twitch-2B during a single action potential in mouse acute cortical slices [24]. ^‡ TN-XXL during systole in heart explants from a transgenic mouse [34].