title: Transmural differences in the properties of ventricular muscle in normal and failing rabbit hearts
Creators: name: Duncan, Alexis Mary
Publisher: name: University of Glasgow
Year: 2002
Subjects: subject: Physiology, molecular biology.

description: It is now well established that electrical, metabolic and mechanical properties vary across the wall of the mammalian ventricle. In this thesis, protein expression, intracellular [Ca2+], and myocyte shortening are examined in myocardium from endocardial and epicardial regions of normal rabbit hearts. These properties were compared with those in equivalent regions of hearts with significant left ventricular dysfunction (LVD) resulting from a ventricular apical infarct. Resting myocyte length was significantly longer in myocytes isolated from LVD hearts but no regional differences in resting myocyte length in sham or LVD myocytes was observed. Fractional shortening was not significantly different between endocardial and epicardial myocytes from both sham and LVD hearts. LVD endocardial myocytes shortened less than myocytes from the comparable region in the sham group. No difference in fractional shortening was observed when comparing epicardial myocytes from sham and LVD hearts. Contraction kinetics were slower in both LVD endocardial and epicardial myocytes. The rest decay effect was more pronounced in endocardial compared with epicardial myocytes in both sham and LVD groups but minimal differences were observed when comparing experimental groups. Peak systolic [Ca2+]i was similar in endocardial myocytes from both experimental groups but was significantly lower in the LVD epicardial group than sham. Peak systolic [Ca2+]i was similar between endocardial and epicardial myocytes in the sham group but LVD epicardial peak systolic [Ca2+]i was lower than endocardial. These results suggest various changes in [Ca2+]i transient amplitude and myocyte shortening in LVD that may be explained by changes in myofilament Ca2+ sensitivity. Transmural protein expression of Calsequestrin, SR Ca2+-ATPase (SERCA) and Na+/Ca2+ exchanger was similar in sham and LVD myocytes. Calsequestrin and Na+Ca2+ exchanger protein expression was significantly increased, and SERCA protein expression was significantly decreased, in LVD myocytes. The link between altered protein expression and altered intracellular [Ca2+] transients in LVD is discussed. Comparison of the amount of protein retrieved from sham and LVD ventricular homogenate samples showed that protein retrieval was similar throughout a range of ventricular tissue wet weights (60 to 1000mg) and in sham and LVD myocardial samples. In contrast, protein retrieved from crude SR preparations (250 - 1000mg) was significantly greater in LVD preparations than sham samples. In addition, crude SR vesicles derived from ventricular samples weighting less than 250mg proved unsuitable for experimental use because of the variable protein retrieval when using such small sample weights. Sources of experimental variation within the Western Blotting technique were also investigated. It was concluded that the major sources of variation were attributable to the electroblotting and the antibody binding steps.