Freshly isolated NRVMs were treated with PDE inhibitors [a general PDE inhibitor IBMX (10 μM), a specific PDE4 inhibitor rolipram (7.5 μM), and a specific PDE3 inhibitor cilostamide (1 μM)], vehicle control DMSO, a β-AR agonist ISO (10 μM), and ISO plus a cell permeable PKA inhibitor PKI (1 μM). After 48 hours treatment, cells were fixed, permeabilized, and immunostained for the cardiomyocyte marker α-actinin. Representative images are shown in 1A. The sizes of NRVMs were quantified using NIH Image J software and plotted in 1B. Data are expressed as mean ± s.e.m.; the number of cells counted is indicated. Student’s t-Tests were performed for statistical analysis. A p-value <0.001 was highly significant (***) while a p-value > 0.05 was not significant (n.s.).