Inhibition of Type 4 Phosphodiesterase by Rolipram and Ginkgo biloba Extract (EGb 761) Decreases Agonist-Induced Rises in Internal Calcium in Human Endothelial Cells

The effects of Gingko biloba extract EGb 761 on 5 isolated, vascular, cyclic nucleotide phosphodiesterase (PDE) isoforms were evaluated. EGb 761 preferentially inhibited PDE4 (IC50=25.1 mg/L), the isoform that is mainly present in endothelial cells, in a competitive manner (Ki=12.5 mg/L). Because changes in cyclic nucleotide levels may affect intracellular calcium ([Ca]i) levels in endothelial cells, we examined the effects of EGb 761 on both resting [Ca]i levels and agonist-induced rises in [Ca]i in single human umbilical vein endothelial cells (HUVECs) in culture. The effects of EGb 761 were compared with those of rolipram, a selective PDE4 inhibitor that increases cellular cAMP levels, and the cAMP analogue dibutyryl cAMP (db-cAMP). EGb 761 (20 and 100 mg/L), rolipram (50 μmol/L), and db-cAMP (100 μmol/L) significantly inhibited histamine-, ATP-, and thrombin-induced [Ca]i increases in HUVECs without modifying resting [Ca]i levels. Similar results were obtained by using a Ca-free bath solution. EGb 761 (100 mg/L), but not rolipram (50 μmol/L) or db-cAMP (100 μmol/L), also inhibited Ca influx into cells having thapsigargin-depleted internal Ca stores and bathed in a Ca-free external solution. Our results are consistent with an inhibition of PDE activity that causes a reduction of agonist-induced increases in [Ca]i in HUVECs, mainly by inhibition of Ca mobilization from internal stores. It thus may be that the cardiovascular effects of EGb 761 involve inhibition of PDE4 activity and subsequent modification of Ca signaling in endothelial cells. (Arterioscler Thromb Vasc Biol. 2000;20:e34-e40.)