Table 1.

Compositions of solutions (mM)

	KCl	NaCl	KMeSO3	CaCl2	CaGluc	MgCl2	MgGluc	HEPES	BAPTA	DibromoBAPTA	HEDTA	d-Glucose
Cytoplasmic
0.1 µM free Ca2+ (standard)	140	5		0.7		2		5	2			5
1–3 µM free Ca2+	140	5		0.9–1.4		2		5		2		5
10–30 µM free Ca2+	140	5		0.8–1.4		2		5			2	5
300 µM free Ca2+	140	5		2.3		2		5	2			5
1 mM free Ca2+	140	5		1		2		5				5
High-K+, 0.1–300 µM free Ca2+	145			*		2		5	*	*	*	5
High-Na+, 3 µM free Ca2+		145		1.4		2		5		2		5
High-Na+, 300 µM free Ca2+		145		2.3		2		5	2			5
Cl¯-free, 3 µM free Ca2+			145		1.4		2	5		2		5
Cl¯-free, 300 µM free Ca2+			145		2.3		2	5	2			5

	NaCl	KCl	CaCl2	MgCl2	HEPES	NaPyr	d-Glucose
External
Standard	140	5	2	2	5	2	9.4
High-K+		145	2	2	5	2	9.4
High-Ca2+			100	2	5		9.4

BAPTA and dibromoBAPTA were added as the tetrapotassium salts and HEDTA as the tripotassium salt. In solutions containing 300 µM free Ca²⁺, the Ca²⁺ buffer (BAPTA) was saturated. Solutions were adjusted to pH 7.4 with the hydroxide of the principal cation, or with Tris base (high-Ca²⁺ external solution). KMeSO₃, potassium methanesulfonate; CaGluc, calcium gluconate; MgGluc, magnesium gluconate; NaPyr, sodium pyruvate.

^*Concentrations of CaCl₂ and Ca²⁺ buffer (BAPTA, dibromoBAPTA, or HEDTA) are as shown for the first set of four solutions.