<p><b>OBJECTIVE</b>To evaluate the effect of therapeutic ultrasound-induced microbubble's cavitation on plasmid gene transduction in rat pulmonary endothelial cells in relation to the changes of membrane fluidity and cytoskeleton structure.</p><p><b>METHODS</b>Rat endothelial cells cultured in vitro were transfected with EGFP plasmid in the presence of protein microbubbles. During the transfection process, the cells were exposed to continuous 2 MHz ultrasonic irradiation for 30, 60, 90, 120 and 180 s (groups A, B, C, D and E, respectively) with the constant mechanical index (MI) of 1.0, or for 60 s with different mechanical index (MI) of 0.5, 0.75, 1.0, 1.5, and 1.8 (groups B1, B2, B3, B4 and B5, respectively). The changes of endothelial cytoskeletal structure and membrane fluidity were evaluated by immunofluorescence staining after the exposure.</p><p><b>RESULTS</b>EGFP gene transduction increase obviously with prolonged echo irradiation and increased MI. The intensity of immunofluorescence staining, which represented endothelial membrane fluidity, was 0.173±0.013, 0.250±0.037, 0.364±0.022, 0.381±0.019, and 0.395±0.009 in groups A-E, as compared with 0.171±0.017, 0.255±0.026, 0.378±0.007, 0.382±0.009 and 0.397±0.008 in groups B1-B5, respectively. The recovery intensity of the immunofluorescence staining representing the changes in microtubulin of the cytoskeleton structure was 159.15±4.79, 188.23±6.20, 205.80±4.48, 208.99±8.34, and 213.70±5.09 in groups A-E, and was 176.84±3.10, 187.57±14.52, 206.41±11.66, 220.12±13.39 and 221.16±12.78 in groups B1-B5, respectively. The endothelial membrane fluidity and microtubule fluorescence recovery intensity increased remarkably compared with the baseline (P<0.01) within the MI range of 0.50-1.0 and the exposure time of 30-90 s, but underwent no further changes in response to prolonged exposure time (180 s) at the MI of 1.5 (P>0.05). No changes in microfilament fluorescence intensity were observed after exposure to different MI or irradiation time.</p><p><b>CONCLUSION</b>Therapeutic ultrasound-mediated albumin microbubble cavitation allows enhances plasmid gene transduction without causing cytoskeleton damages. Increased endothelial membrane fluidity and changes in cytoskeleton structure, especially microtubulin, partially contribute to this enhancement.</p>