Extracellular stimuli induce class IIb HDAC catalytic activity in cultured cardiac myocytes and fibroblasts. HDAC activities were measured as described for Figure 3. (A) NRVMs were left untreated (−) or stimulated for 72 hrs with NE (10 μM), PE (10 μM) or ISO (1 μM), then harvested for HDAC activity measurements. (B) NRVMs were cultured in the absence (−) or presence of NE (10 μM), PGF2α (10 μM), or ET-1 (25 nM) for 72 hrs prior to measuring HDAC activity in lysates. (C) ARVMs were treated with NE (10 μM), PE (20 μM), PGF2α (10 μM) or ET-1 (25 nM) for 72 hrs and harvested for HDAC activity assays. (D) ARVFs were treated with FBS (10%) or IL-1β (10ng/ml) for 48 hrs prior to harvesting cells for HDAC activity assays. Values for A – D represent averages (n = 3 per condition) +SEM. *P < 0.05 versus respective control.