Fig. 5.

Caffeine decreases the threshold for eliciting a regenerative response. A, [Ca²⁺]_i transients were elicited in the presence of 2.5 or 5.0 mm caffeine as indicatedabove the traces. Trains (2 Hz) of four action potentials were delivered every 2.5 sec until a regenerative rise in [Ca²⁺]_i had started. Thehorizontal arrows indicate the threshold [Ca²⁺]_i for triggering CICR. Thevertical dotted lines mark termination of the stimulus.B, Dependence of the threshold on caffeine concentration obtained for 5–14 cells. Data points are mean ± SEM for responding cells.