Abstract 20259: Lower Surface Content of L-type Calcium Channel Impairs Cardiac Contractility in Heart Failure Patients
Introduction: Heart failure is a growing epidemic, yet the mechanisms by which damaged hearts progress to end-stage disease remain unclear. A typical aspect of failing hearts is altered calcium signaling. The cardiac calcium transient is initiated by L-type calcium channels (Cav1.2). Normal cardiac calcium transient begins with membrane depolarization which initiates calcium entry through T-tubule Cav1.2, triggering a large release of calcium by the intracellular sarcoplasmic reticulum. We recently found that forward trafficking of Cav1.2 channels to T-tubules is facilitated by the membrane curvature and T-tubule protein BIN1. However, Cav1.2 channels trafficking in failing cardiomyocytes remains unidentified.
Hypothesis: In failing cardiomyocytes, there is abnormal Cav1.2 forward trafficking and therefore lower surface content of Cav1.2, resulting in impaired cardiac contractility.
Methods and Results: Using cardiomyocytes isolated from non-failing and end-stage failing human hearts, we found that overall Cav1.2 messenger and protein expression levels are the same by quantitative rt-PCR, immunofluorescence, and western blot. However, in failing hearts, Cav1.2 is internalized. Furthermore, in failing hearts, the protein and message levels of the Cav1.2 T-tubule anchor protein BIN1 are lower, diminishing a key mechanism by which Cav1.2 channels get to T-tubules. In adult mouse cardiomyocytes, lentiviral mediated shRNA knockdown of BIN1 decreases surface level of Cav1.2 and impairs the intracellular calcium transient. In zebrafish hearts, morpholino mediated BIN1 knockdown diminishes the calcium transient and causes severe ventricular dysfunction. From patients with differing stages of idiopathic heart failure, we found that cardiac BIN1 levels are proportional to cardiac output and prognosticate heart failure development.
Conclusions: The data support a model whereby surface membrane localization of Cav1.2 is reduced during heart failure as a result of limited BIN1 expression, impairing the calcium transient and contributing to excitation-contraction uncoupling in human heart failure. This cellular mechanism can help explain heart failure progression and also help prognosticate heart failure outcomes.
- © 2010 by American Heart Association, Inc.