Intracellular cyclic AMP levels in endothelial cells subjected to cyclic strain in vitro

Human saphenous vein endothelial cells (EC) were grown to confluence in fibronectin-coated culture plates with flexible membrane bottoms and maintained in M-199 supplemented with substrates. One hour prior to experimentation 5 mM IBMX, a phosphodiesterase inhibitor, was added. Vacuum was used to deform the membrane bottoms to 24% strain at 60 cycles/min (0.5 sec elongation alternating with 0.5 sec relaxation). After 10-60 min of cyclic strain, or upon exposure of EC to 100 microM forskolin or 0.1 microM galanin, intracellular cyclic AMP (cAMP) was measured by radioimmunoassay. In parallel experiments, tissue plasminogen activator (tPA) secretion was determined after 24 hr of cyclic strain in the absence or presence of forskolin or galanin. The results demonstrate that exposure of EC to cyclic strain led to no change in cAMP levels and confirmed our previous observation that tPA secretion was enhanced with cyclic strain. Addition of forskolin, which led to an almost 10-fold increase in cAMP levels, or galanin, which led to a 34% decrease in cAMP levels, did not significantly alter the rise in tPA induced by cyclic strain.