Interventricular differences in myofilament function in experimental congestive heart failure.

This study was conducted to identify molecular mechanisms which explain interventricular differences in myofilament function in experimental congestive heart failure (CHF). CHF was induced in rats by chronic aortic banding or myocardial infarction for 32-36 weeks. Right and left ventricular (RV, LV) myocytes were mechanically isolated, triton-skinned, and attached to a force transducer and motor arm. Myofilament force-[Ca(2+)] relations assessed maximal Ca(2+)-saturated force (F (max)) and the [Ca(2+)] at 50% of F (max) (EC(50)). Myofilament protein phosphorylation was determined via ProQ diamond phospho-staining. Protein kinase C (PKC)-α expression/activation and site-specific phosphorylation of cardiac troponin I (cTnI) and cardiac troponin T (cTnT) were measured via immunoblotting. Relative to controls, failing RV myocytes displayed a ~45% decrease in F (max) with no change in EC(50), whereas failing LV myocytes displayed a ~45% decrease in F (max) and ~50% increase in EC(50). Failing LV myofilaments were less Ca(2+)-sensitive (37% increase in EC(50)) than failing RV myofilaments. Expression and activation of PKC-α was increased twofold in failing RV myocardium and relative to the RV, PKC-α was twofold higher in the failing LV, while PKC-ß expression was unchanged by CHF. PKC-α-dependent phosphorylation and PP1-mediated dephosphorylation of failing RV myofilaments increased EC(50) and increased F (max), respectively. Phosphorylation of cTnI and cTnT was greater in failing LV myofilaments than in failing RV myofilaments. RV myofilament function is depressed in experimental CHF in association with increased PKC-α signaling and myofilament protein phosphorylation. Furthermore, myofilament dysfunction is greater in the LV compared to the RV due in part to increased PKC-α activation and phosphorylation of cTnI and cTnT.

The ligament of Marshall as a parasympathetic conduit.

The objective of the study was to investigate the morphology, distribution, and electrophysiological profile of the autonomic fibers that innervate the ligament of Marshall (LOM). Gross anatomical dissections were performed in 10 dogs. Sections of the left vagus nerve, left stellate ganglion, and the LOM were immunostained to identify adrenergic and cholinergic nerves. Hearts were also stained for acetylcholinesterase to identify epicardial cholinergic nerves. In vivo electrophysiological studies were performed in another 10 dogs before and after LOM ablation. The anatomical examination revealed that the LOM is innervated by a branch of the left vagus. Immunohistochemistry confirmed that these nerve bundles are predominantly cholinergic (cholinergic-to-adrenergic ratio of 12.6 +/- 3.9:1). Cholinergic nerves originating in the LOM were found to innervate surrounding left atrial structures, including the pulmonary veins, left atrial appendage, coronary sinus, and posterior left atrial fat pad. Ablation of the LOM significantly attenuated effective refractory period shortening at distant sites, such as pulmonary veins and left atrial appendage, in response to vagal stimulation (vagal-induced ERP decrease in the left atrium: baseline vs. postablation = 17 vs. 4%; P = 0.0056). In conclusion, the LOM contains a predominance of cholinergic nerve fibers. Cholinergic fibers arising from the LOM innervate surrounding structures and contribute to the electrophysiological profile of the left atrium. These findings may provide a basis for the role of the LOM in the genesis and maintenance of atrial fibrillation.