Arginine–glycine–aspartic acid (RGD)‐containing peptides inhibit the force production of mouse papillary muscle bundles via α5β1 integrin

Integrins are considered to be an important mechanosensor in cardiac myocytes. To test whether integrins can influence cardiac contractile function, the force–frequency relationships of mouse papillary muscle bundles were measured in the presence or absence of a synthetic integrin‐binding peptide, GRGDNP (gly–arg–gly–asp–asn–pro). Results demonstrate that in the presence of an arginine–glycine–aspartic acid (RGD)‐containing synthetic peptide, contractile force was depressed significantly by, 28% at 4 Hz, 37.7% at 5 Hz and 20% at 10 Hz (n= 6, P < 0.01). Treatment of myofibres with either protease‐generated fragments of denatured collagen (Type I) or denatured collagen that contain the RGD motif, also reduced force production significantly. An integrin‐activating antibody for β1 integrin inhibited the force similar to synthetic RGD peptide. Function‐blocking integrin antibodies for α5 and β1 integrins reversed the effect of the RGD‐containing peptide, and α5 integrin also reversed the effect of proteolytic fragments of denatured collagen on contractile force, whereas experiments with function‐blocking antibody for β3 integrin did not reverse the effect of RGD peptide. Force–[Ca2+]i measurements showed that the depressed rate of force generation observed in the presence of the RGD‐containing peptide was associated with reduced [Ca2+]i. Data analyses further demonstrated that force per unit of Ca2+ was reduced, suggesting that the myofilament activation process was altered. In addition, inhibition of PKC enzyme using the selective, cell‐permeable inhibitor Ro‐32‐0432, reversed the activity of RGD peptide on papillary muscle bundles. In conclusion, these data indicate that RGD peptide, acting via α5β1 integrin, depresses the force production from papillary muscle bundles, partly associated with changes in [Ca2+]i and the myofilament activation processes, that is modulated by PKCɛ.