The endothelium is known to sense and respond to its physical environment. but the underlying mechanisms and early events of endothelial cell mechanotransduction are not well understood. The present study measured G protein activation by mechanical strain in human umbilical vein endothelial cells (HUVEC) directly by photoincorporation of a hydrolysis resistant, radiolabeled GTP analog. Ten percent uniaxial strain at a strain rate of 20% s(-1) over 1 min activated a 38 kDa Galpha subunit 167 +/- 17%, relative to controls, while 2% cyclic strain failed to significantly activate the protein (117 +/- 19%). A single cycle of 10% strain at 20% s(-1) strain rate activated the Got subunit 152 +/- 25%, while activation at the same strain but lower strain rate (0.3% s(-1)) was not significantly different from controls (116 +/- 12%). Western blot analysis identified the 38 kDa protein its Galpha(q.11), These results demonstrate the rapid activation of G proteins in HUVEC by cyclic uniaxial strain in a strain- and strain rate-dependent manner. (C) 2002 Elsevier Science (USA). All rights reserved.