Table 1.

Internal solution composition

Solution	Ca2+	Mg2+	EGTA	HDTA	Caffeine	Rhod-2	Fura-red
Standard-0 Ca2+	0	1	1	49	0	0.01	0
Standard-100 Ca2+	0.0001	1	1	49	0	0.01	0
Standard-200 Ca2+	0.0002	1	1	49	0	0.01	0
Standard-800 Ca2+	0.0008	1	1	49	0	0	0
Mild inhibitory	0.0001	0.4	1	49	0	0.01	0
Medium EGTA	0	1	10	40	0	0.01	0
Medium EGTA release	0	0.01	10	40	3	0.01	0
High EGTA	0.0001	1	50	0	0	0	0.05
Low Mg2+	0	0.01	1	49	0	0.01	0
High EGTA release	0	0.01	50	0	5	0	0.05

All concentrations are in mm. Additionally, solutions contained (mm): K⁺, 126; Na⁺, 36; creatine phosphate, 10; ATP, 8; Hepes, 90; n-benzyl-p-toluene sulphonamide, 0.05. Mg²⁺ was added as MgO and Ca²⁺ was added as Ca₂CO₃. Note that ‘Ca²⁺’ and ‘Mg²⁺’ refer to the free ionic compositions in solution and that the total concentrations of Mg and Ca were much higher. Osmolality was adjusted to 290 ± 10 mosmol kg⁻¹ with sucrose. Note also that HDTA²⁻ (Fluka, Buchs, Switzerland) is used as the anion replacement of EGTA²⁻. pH was adjusted to 7.1 with KOH in all solutions.