Fig. 4. Effect of isoproterenol (ISO) on I_Ca and Ca²⁺ transient. (A) I_Ca elicited by repetitive 200 ms depolarizations (0.2 Hz) to 0 mV in the absence (black line) and presence (gray line) of 1 µmol l^–1 ISO. (B) Ca²⁺ transients recorded simultaneously with I_Ca in A. Traces are averages of recordings from 7 cells at steady state. Filled symbols + solid line, no ISO; gray symbols + dotted line, + ISO.