Figure 3. β-AR- and Epac-induced Ca²⁺ sparks.

A, B. Raw Ca²⁺ sparks in intact mouse ventricular myocytes. C. Ca²⁺ spark frequency (CaSpF) was increased by ISO (100 nM), but not by NOS-inhibitor L-NPA (5 mM, 10 min). However, L-NPA blocked ISO-induced increase in CaSpF (n=9, 6, 5 and 5 myocytes). D. 8-CPT (10 mM, 2 min) induced increased CaSpF, while neither NOS inhibition (100 μM L-NAME, 5 min) nor PI3K inhibition (10 μM LY294002) altered baseline CaSpF. Both L-NAME and LY294002 prevented 8-CPT-induced CaSpF (n=21, 10, 13, 13, 7 and 7 myocytes, respectively; * p<0.05). Resting fluorescence was not significantly altered by L-NPA, 8-CPT, L-NAME or LY94002, but was slightly increased (15%) by ISO, which may be secondary to higher CaSpF.