Myosin Ii Is Important For Endothelial Barrier Function But Is Not Involved In Sphingosine-1-Phosphate-Induced Endothelial Barrier Enhancement

Recently we discovered an association between local lamellipodia formation/turnover and endothelial barrier function. To determine cause‐effect, we tested the hypothesis that selective blockade of lamellipodia formation with the myosin II inhibitor (−)blebbistatin would disrupt endothelial barrier integrity. We also investigated whether myosin II inhibition affects sphingosine‐1‐phosphate (S1P)‐induced endothelial barrier enhancement. Transendothelial electrical resistance (TER) of confluent cultured human umbilical vein endothelial cells (HUVEC) served as an index of barrier function. HUVEC expressing GFP‐actin were used to study local lamellipodia dynamics. The results show that 100 μM (−)blebbistatin caused a significant decrease in TER, while (+)blebbistatin caused no change from baseline. In addition, (−)blebbistatin, caused local lamellipodia protrusion frequency to drop nearly 90%, while (+)blebbistatin caused no change. S1P (2 μM) increased TER and caused a brief, coordinated protrusion of the edges of individual endothelial cells. Pretreatment with (−)blebbistatin did not inhibit the S1P‐induced increase in TER. Our data indicate that MLC‐2‐driven local lamellipodia contribute to endothelial barrier function. However, an myosin II‐independent mechanism drives S1P‐induced edge protrusions and endothelial barrier enhancement. Supported by NIH R01HL098215.