Figure 8. Effect of GSNO_imm treatment on SR Ca²⁺ accumulation.

Force responses elicited in a skinned EDL fibre upon fully emptying the SR of all Ca²⁺ by exposure to caffeine–low [Mg²⁺] release solution (small arrows) (see Methods). Time integral (‘area’) of force responses indicative of SR Ca²⁺ content reached after having loaded the SR for the indicated time (1 or 3 min) in a load solution with indicated free [Mg²⁺] (1 or 10 mm) at pCa 6.7, or at pCa 6.4 (response ‘i’). Following the 2 min treatment with GSNO_imm, the fibre was treated with DTT (10 mm, 10 min) to restore the normal Ca²⁺ sensitivity of contractile apparatus. After GSNO_imm treatment, the ability of the SR to accumulate Ca²⁺ during a 3 min loading period in 1 mm Mg²⁺ was greatly depressed (area of response is much smaller in ‘g’ than in ‘a’). Raising the [Mg²⁺] in the load solution to 10 mm markedly increased the amount accumulated with 3 min loading (compare ‘h’ with ‘g’). Mean data shown in Fig. 9B.