Structure and Function of Intracellular Calcium Channels
The goal of the laboratory’s research is to understand the molecular mechanisms underlying cardiac muscle and skeletal muscle Ca2+ signaling. The release of Ca2+ ions in striated muscle is controlled by a large ion channel that is identical with protein bridges that span the gap between the cell membrane and an intracellular Ca2+-storing, membrane-bound compartment, the sarcoplasmic reticulum. Cloning and construction of the full-length cDNA encoding the 5037 amino acid residues of the Ca2+ release channels has enabled us to identify amino acid residues that line the ion channel pore, determine ion selectivity, and are responsible for the high ion conductance of the release channels. This work is pertinent to understanding the cellular basis of muscle diseases such as central core disease and malignant hyperthermia. We are also studying the functional roles of regulatory thiols that are modified in the Ca2+ release channels by nitric oxide and changes in oxygen tension, which addresses more global concepts in muscle Ca2+ signaling. This work has demonstrated the relationship between nitric oxide metabolism and Ca2+ signaling, and identified the Ca2+ release channel as a key oxygen sensor in skeletal muscle. Current work aims to identify regulatory redox-sensitive thiols of cardiac and skeletal Ca2+ release channels by mass spectrometric analysis and mutagenesis. These studies have the potential to reveal pathways that protect the heart during ischemia and recovery. A third major goal of the laboratory’s current work is to delineating the functional role of calmodulin in sarcoplasmic reticulum Ca2+ release. Our recent mutagenesis studies leading to the identification of the calmodulin regulatory sites of the Ca2+ release channels has enabled us to prepare a genetically modified mouse deficient in regulation of the cardiac Ca2+ release channel by calmodulin. We find that impaired calmodulin regulation of the cardiac release channel leads to abnormal sarcoplasmic reticulum Ca2+ release, cardiac hypertrophy, and early death of the homozygous mutant mice. As our experiments proceed we expect to gain new insights into the complex mechanism of sarcoplasmic reticulum Ca2+ release and how impaired regulation of the release channel by calmodulin leads to cardiac hypertrophy and heart failure, one of the most frequent causes of death in man.