Table 1. Initial studies examining resting calcium in dystrophic muscle based on fluorescent dyes.

Study	mdx [Ca2+] nM	WT [Ca2+] nM	Dye	Muscle	Isolation technique	Dye loading	Calibration parameters	Temperature
Turner (23)	92±9.8	40±2.8	Fura-2 tetracarboxylate	FDB	Mechanical dissection	Microinjection	Identical between mdx and WT	37 °C
Turner (23)	282±13	201±6	Fura-2/AM	FDB	Mechanical dissection	Passive loading	Identical between mdx and WT	37 °C
Gailly (24)	123±12	125±9	Fura-2/AM	Soleus	Collagenase digestion	Passive loading	Different between mdx and WT	20 °C
Gailly (24)	45.2±3	44.9±4	Fura-2/AM	FDB	Collagenase digestion	Passive loading	Different between mdx and WT	20 °C
Head (12)	45.7+4.1	46.2±3.9	Fura-2 tetracarboxylate	FDB	Collagenase digestion	Microinjection	No significant difference	22 °C
Collet (25)	48±7	56±5	Indo-1	FDB and interosseous	Collagenase digestion	Microinjection	No significant difference	20–22 °C

Abbreviations: FDB, flexor digitorum brevis; WT, wild-type; [Ca²⁺], calcium concentration. The initial study in the mdx mouse by Turner found a difference in basal intracellular calcium in myofibers between the mdx and the C57 mouse. They found this difference regardless of whether they used active or passive loading. Interestingly, this study was the only study to utilize mechanical dissection and the only study to find a statistically significant difference. Overall, technical challenges associated with photometric measurement of calcium, in conjunction with challenges associated with fiber isolation and selection bias, may explain the negative data that were also observed