Standard Reaction Buffer for Ca²⁺ Indicators

In purified water (>18 MΩ), prepare 150 mm HEPES. Set the pH to 7.3 with NaOH or KOH, and set the ionic strength to the desired value with NaCl or KCl. (Use 100 mm NaCl for an ionic strength of 150 mm because at pH 7.3, approximately one-third of HEPES is in solution as a free ion.) This solution does not perish. It is best kept dark and/or cold (4°C) to prevent bacterial growth.

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