Confocal Fluorescence Microscopy of Cardiac Myocytes

Dr. John Bridge

The overarching goal of Dr. Bridge's research is to provide insights into the mechanisms of excitation contraction coupling in the heart. It is now widely accepted that calcium induced calcium release (CICR) is the basic mechanism of cardiac excitation contraction coupling. A small rise in free calcium in the vicinity of the sarcoplasmic reticulum causes the release of much greater quantities of calcium, which in turn activates contraction. The local release events, so-called calcium sparks, are considered to be the elementary release events which when summed produce a single calcium transient. Sparks and their relationship to ion channels involved in their production are subject of experimental and theoretical studies of Dr. Bridge's current grant.

Specific aims of this grant are to study rabbit ventricular myocytes and investigate (1) the dependence of spark probability on the extracellular calcium concentration [Ca]O, (2) the fluorescence produced by calcium current its relationship to the spark probability, and (3) the relationship between spark sites and structural morphology. The project is aimed at gathering and evaluating evidence that clusters of L-type calcium channels are required to trigger sparks at high probability during a calcium transient. Dr. Bridge argues that spark probability is steeply dependent on size of the clusters of L-type calcium channels that trigger sparks. Since L-type calcium channels are reduced in diseased heart, this phenomenon could explain the extinction of calcium transients in disease and as such establishes an aspect of health relatedness of this project.

Several co-investigators and consultants from the University of Utah, Maryland, and Auckland are involved in the project, which was funded by the National Heart, Lung and Blood Institute for a duration from March 2004 to April 2009.

The major measurement technique in this project is confocal fluorescence microscopy, which allows the determination of sparks and the underlying variations of intracellular calcium concentrations. The center can support this project by providing software to improve imaging, analysis, and visualization of multidimensional data from confocal fluorescence microscopy.

This is an entirely new collaboration, made possible by the addition of the image and geometric modeling core to the Center. Dr. Bridge has adequate funding for his own part of the project, however, improvements in image processing support may open up new opportunities for study that could form the basis of additional projects and external grant applications.