Kinetics of guinea pig Ca2+c transients. Ca2+c transients were measured from a guinea pig heart loaded with Rhod-2AM, placed in the chamber described in Figure 12.17.12, and perfused with cytochalasin-D to abate motion artifacts. The downstroke of Ca2+c transients exhibited complex biphasic recoveries to baseline and decreases in durations that were dependent on Ca2+ in the perfusate: (A), 1; (B), 0.75; (C), 0.5; and (D), 0.25 mM free Ca2+.