RA were untreated (Ctrl) or stretched to twice the ex vivo resting length (Stretch). The stretched segments were cut into 2mm rings and incubated for 1 hour in heparinized PlasmaLyte in the absence or presence of apyrase (Apy, 4 units/mL), the P2X7R inhibitor A438078 (A43, 100μM), or the p38 MAPK inhibitor SB203580 (SB, 20μM). Tissues were suspended on a muscle bath, contracted with phenylephrine (5×10−7M) and contractile responses were calculated (n=9–13, *p<0.05 compared to stretch injured tissue).