['The mechanism by which hemodynamic forces influence the function of the endothelium lining a blood vessel are unknown. The aim of this study was to determine the effect of in vitro cyclic strain on endothelial cell (EC) activation of protein kinase C (PKC).', 'Confluent bovine aortic ECs grown on flexible-bottomed culture plates were subjected to 24% maximum strain at a frequency of 60 cycles/min for 24 hours. Changes in PKC activity and evidence of translocation from cytosol to membrane fractions were assessed by immunocytochemical staining of ECs with antibodies specific to PKC and direct measurement of PKC activity in cytosol and membrane. To determine whether activation of PKC was responsible for some effects of cyclic stretch on ECs, a specific PKC inhibitor, calphostin C, was added to ECs subjected to cyclic stretch for 5 days and control ECs grown under static conditions.', 'Immunocytochemical staining of ECs demonstrated translocation of PKC alpha- and beta-antibody fluorescence from the cytosol to the perinuclear and nuclear regions in ECs subjected to cyclic strain. This was confirmed by direct measurements of PKC activity, which demonstrated an early transient translocation of PKC activity from cytosol to membrane fraction at 10 seconds followed by a sustained elevation in PKC activity in the membrane at 100 seconds. Calphostin C abrogated the increase in EC proliferation that occurs in response to stretch.'] Is protein kinase C a mediator of the adaptation of vascular endothelial cells to cyclic strain in vitro?