Molecular cardiac physiology, cardiac contractility, congenital heart disease, calcium regulation in the heart

The research program in the Cardiac Membrane Research Lab (CMRL) focuses on the cellular and molecular mechanisms by which the heart adapts to physiological, pathological and environmental perturbations. The strength of cardiac muscle contraction is regulated by the cytosolic Ca2+ activity ([Ca2+]i) on a beat-to-beat basis. We focus, therefore, on factors which control [Ca2+]i in the heart. These studies are multidisciplinary and conducted at three different levels of organization. The first and most integrative approach makes use of isolated single cardiac cells in which speed of shortening is assessed by video microscopy using edge detection and the [Ca2+]i transient is determined on line with indo-1 fluorescence microscopy. The second approach involves measuring Ca2+ movement across isolated membranes using voltage clamp, planar lipid bilayers and/or radioisotopic techniques. The third approach includes the cloning, sequencing and expression of proteins critically involved in Ca2+ handling. These proteins include the: L-type voltage-dependent Ca2+ channel (DHPR), which controls Ca2+ influx; Na+/Ca2+ exchanger (NCX), which is the primary mechanism of Ca2+ efflux; and troponin C, a Ca2+ binding protein which is crucial in the initiation of contraction. These proteins and mutants produced by site-directed mutagenesis are studied in vitro as well as in the reconstituted muscle fibre. With these techniques, we are investigating the mechanisms by which these proteins are regulated in different species to meet a variety of physiological, pathological and environmental demands.