Gadolinium prevents stretch-mediated contractile dysfunction in isolated papillary muscles

We tested the hypothesis that overstretching the myocardium could induce an d/or exacerbate contractile dysfunction via stretch-activated (SA) ion chan nels. Maximum developed tension (T-max), normalized to a control value, was compared in guinea pig papillary muscles held at one of three resting leng ths (physiological stretch, overstretch, and unloaded) for 85 min. Overstre tched muscles exhibited decreased contractile force (T-max = 0.77 +/- 0.03) compared with physiological and unloaded muscles (T-max = 0.93 +/- 0.05 an d 1.03 +/- 0.07, respectively). Gd3+, an SA channel antagonist, eliminated the adverse effect of overstretching (T-max = 0.98 +/- 0.06), but nifedipin e, a dihydropyridine (DHP) antagonist of L-type calcium channels, did not ( T-max = 0.82 +/- 0.04). Exposure to modified hypoxia-reoxygenation (MHR) du ring physiological stretch resulted in decreased contractility (T-max = 0.6 3 +/- 0.07), an effect that was exacerbated by overstretching (T-max = 0.44 +/- 0.04). Gd3+ mitigated the effects of overstretch during MHR (T-max = 0 .64 +/- 0.05), but DHP did not (T-max = 0.48 +/- 0.04). These data suggest that overstretching of the myocardium contributes to contractile abnormalit ies via SA channels that are distinct from L-type calcium channels.