Effect of protein kinase A inhibition on ATP-induced vWf release. Confluent HUVECs grown on 24-well plates were incubated for 30 minutes in the presence or absence of Rp-8-CPT-cAMPS (Rp). ATP and/or IBMX were then added, and the incubation continued for 30 additional minutes. Results are expressed as vWf released per well during the last 30 minutes. Basal release was calculated as half the vWF released during the 1-hour incubation (assuming continuous constitutive release over 1 hour, see Fig 2). See text for statistical analysis.