Biochemical mechanism(s) of stunning in conscious dogs

The mechanism(s) underlying contractile dysfunction in cardiac stunning is not completely understood. The expression and/or the phosphorylation state of cardiac Ca2+ homoeostasis-regulating proteins might be altered in stunni ng. We tested this hypothesis in a well-characterized model of stunning. Co nscious dogs were chronically instrumented, and the left anterior descendin g artery (LAD) was occluded for 10 min. Thereafter, reperfusion of the LAD was initiated. Tissues from reperfused LAD (stunned) and Ramus circumflexus (control) areas were obtained when left ventricular regional wall thickeni ng fraction had recovered by 50%. Northern and Western blotting revealed no differences in the expression of the following genes: phospholamban, calse questrin, sarco( endo) plasmic reticulum Ca2+-ATPase 2a, and the inhibitory subunit of troponin I (TnI). However, the phosphorylation state of TnI and phospholamban were reduced in the LAD area. Fittingly, cAMP levels were re duced by 28% (P< 0.05). It is concluded that the contractile dysfunction in cardiac stunning might be mediated in part by decreased levels of cAMP and subsequently a reduced phosphorylation state of phospholamban and TnI.