Murine ventricular myocytes respond to local axial stretch with SMIC, i.e. activation of non-selective cation channels (TRPC6) and deactivation of inwardly rectifying K+ channels (Kir2.3). Here, we analyzed signalling cascades responsible for SMIC. SMIC was mimicked by exogenous H2O2 (EHMIC). Endogenous H2O2 may derive from NADPH oxidase since DPI blocked SMIC. SMIC was insensitive to ecSOD (catalase) but sensitive to icSOD (DETC) which also blocked EHMIC suggesting that O2- rather than H2O2 were the active principle. SMIC and EHMIC were absent in cells deprived of NO (NO quench with TPIO, NOS inhibition by L-NAME or LNMMA). Analysis of k.o. -/- mice indicated involvement of eNOS but not nNOS in SMIC signalling. SMIC was mimicked by exogenous peroxynitrite and inhibited by peroxynitrite quench (uric acid). Detubulization or filipin treatment blocked SMIC suggesting the T-tubular caveolae could provide a scaffold for spatially aligned generation of O2- and NO favouring peroxynitrite formation. SMIC was mimicked by ATII and blocked by losartan suggesting involvement of AT1R in the mechanical activation of NADPH oxidase.

We suggest that mechanical integrin stimulation activates AT1R and in turn eNOS and NADPH oxidase. Within caveolae, stretch- induced O2- and NO react to form peroxynitrite that can diffuse as a second messenger throughout the whole cell to induce SMIC.