To investigate the hypotheses of this project transgenic mice, rat models of disease and new cultured cell methods are being used to illuminate the molecular causes of Ca2+ signaling defects in heart disease. We use an ensemble of high resolution, state-of-the-art approaches including confocal microscopic imaging, patch clamp methods and molecular biology techniques to examine how local calcium signals depend on the cardiac cytoskeleton or may be influenced by it. We are also investigating how the transverse tubules work in adult heart cells and how these structures are maintained. We are also investigating how the Na+/Ca2+ exchanger, the Na, K ATPase, Ca2+ channels, Na+ channels and K+ channels interact with the cytoskeleton and how these interactions influence cardiac Ca2+ signaling. Finally, we are investigating the stress activated kinase signaling cascade, the JNK signaling pathway (see Project 2), to determine how it influences cardiac Ca2+ signaling and arrhythmogenesis.
We have been studying the ankyrin B homozygous and heterozygous knockout mouse along with Terry Rogers and his team, Vann Bennett (Duke University) and his team and Dennis Escande (INSERM, Nantes, France) and his team. Ankyrin B is an adaptor protein that links diverse cytoskeletal components in heart cells to ion channels, transporters and signaling complexes. We have been able to show that in the Ank B +/- animal, there is a significant defect in Ca2+ signaling that underlies the development of a long QT syndrome (LQTS) and sudden cardiac death. Human patients with a non-functioning mutation in Ank B develop LQTS type IV, which is recapitulated in the mouse Ank B +/-. The defect reduces the amount of Na+/Ca2+ exchanger and Na, K ATPase in the t-tubular membranes of mouse cardiomyocytes. This leads to an increase in the [Ca2+]i transient and in Ca2+-activated membrane current. The work is significant because we have identified, for the first time, a new class of lethal cardiac arrhythmias, LQTS 4, due to disruption of the cellular cytoskeleton.