Figure 1. Steady-state caffeine-induced responses at 2 and 4 min loading periods.

Simultaneous records of the 340 nm/380 nm fluorescence ratio (lower panel) and isometric tension (upper panel) from a saponin-permeabilized muscle fibre bundle in the presence of 100 nm bathing Ca²⁺. Caffeine (20 mm) was briefly applied (for 1.5 s) at 2 min intervals as indicated. Each application resulted in a transient increase in the fluorescence ratio and a corresponding tension response. After 4 control responses, the time between caffeine applications was increased from 2 to 4 min.