Figure 5. Recovery of SR Ca²⁺ release is not inhibited by myoplasmic ATP removal but is inhibited by the presence of myoplasmic P_i.

The recovery of the peak force response to caffeine after prior inhibition by 50 mm P_i was plotted against the length of time fibres were washed (30 s to 2 min) under various myoplasmic conditions: □, presence of myoplasmic ATP, cf. Fig. 3A; ▪, absence of myoplasmic ATP, cf. Fig. 3B; and •, absence of myoplasmic ATP and presence of 30 mm myoplasmic P_i, cf. Fig. 3C. Note that the response to caffeine recovered to a similar extent if fibres were washed in either the presence or absence of ATP, but did not recover when 30 mm P_i was also present during the washout. Points represent mean data ±s.e.m. from 3–14 fibres.