Standard Intracellular Solution

145 mm potassium gluconate

4 mm NaCl

4 mm Mg-ATP

0.3 mm Na-GTP

14 mm Na-phosphocreatine

10 mm HEPES

Adjust the pH to 7.3 with KOH. The final osmolarity is typically ∼297 mOsm. Supplement this solution with the Ca²⁺ indicator of choice. The recommended final concentrations of some indicators are as follows: 100–250 µm bis-Fura-2, 25–100 µm OGB-1, 500 µm Furaptra, or 300 µm OGB-5N. (Because the final concentration of the indicator is much lower than the concentrations of the other solution components, there is no need to correct for osmotic changes.) Note that there are no other added Ca²⁺ buffers.

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