of mineralocorticoid receptors in the heart blunts the Anrep effect.

PÉREZ NG; DÍAZ RG; MORGAN PE; CINGOLANI HE

Los Angeles

Congreso; Scientific Sessions of The American Heart Association; 2012

The American Heart Association

The stretch-induced increase of cardiac force is biphasic. A first abrupt increase(Farnk-Starling mechanism) is followed by a slower response that takes minutesto develop, which is believed to be the in vitro manifestation of the Anrep effect.This slow force response (SFR) is due to an increase in the intracellular Ca2+transient. Although the cause of the increase in Ca2+ is controversial, anincreased NHE1 activity as result of a stretch-triggered autocrine/paracrinemechanism was proposed to be crucial. Furthermore, based on pharmacologicalapproaches we have recently suggested a role for mineralocorticoid receptors(MR) activation in the signaling pathway to the SFR. However, a recent report insmooth muscle cells called attention to the fact that MR inhibitors spironolactoneor eplerenone can also affect signaling pathways that do not depend on MRactivation. Therefore definitive evidence about the participation of MR in the SFRdevelopment needs of MR silencing by molecular techniques. In this study, aninterference RNA sequence (small hairpin) able to mediate specific MR knockdownwas incorporated into a lentiviral vector (l-shMR) and injected into the leftventricular wall of rat myocardium. Injection of a vector expressing anon-silencing sequence (scramble) served as control. Rats were sacrificed onemonth after injection. Myocardial MR protein expression was determined and theSFR as well as the stretch-triggered NHE1-mediated increase in pHi in theabsence of bicarbonate was evaluated in isolated papillary muscles. Hearts withl-shMR showed reduced MR protein expression (100 ± 5.7 %, n=8, scramble vs.57 ± 5.6 %, n=9, l-shMR, P<0.05) as well as inhibition of the SFR (in % of initialrapid phase: 125.9 ± 1.8, n=8, scramble, vs. 103.9 ± 1.3, n=8, l-shMR, P<0.05)and of the stretch-induced increase in pHi in bicarbonate free medium ( pHunits: 0.156 ± 0.025, n=7, scramble, vs. 0.009 ± 0.015, n=10, l-shMR, P<0.05).These data provide unequivocal support to our proposal that MR activation iscrucial in the stretch-triggered myocardial mechanism leading to NHE1 activationthat determines the Anrep effect.