Table 1. Composition of each cation selective microelectrode and concentrations of aqueous calibration solutions.

	Ionophore	Aqueous filling solution	Aqueous calibration solutions
Na+	Fluka- Sodium Ionophore II- Cocktail A	500 mM NaCl	500, 250, 125, 62.5, 31.3 mM NaCl
K+	Fluka- Potassium Ionophore I- Cocktail B	100 mM KCl	100, 50, 25, 12.5, 6.3, 3.1 mM KCl
Ca 2+	Fluka- Calcium Ionophore I- Cocktail A	100 mM CaCl2	100, 10, 1, 0.1, 0.01 mM CaCl2(CALBUF-1, World Precision Instruments)