Research Description
The research interests in my laboratory concern the mechanisms controlling calcium ion fluxes in excitable cells, especially skeletal muscle and cardiac myocytes. Stimulation of these cells causes calcium ions to be released from the intracellular calcium-sequestering organelle, the sarcoplasmic reticulum. The resulting elevation of cytosolic calcium serves as a "second messenger" in these cells, causing contraction and activation of metabolic processes and gene transcription in muscle cells. The techniques for measuring these changes in intracellular calcium involve the use of electrophysiological and patch-clamp methods to stimulate the cell and confocal optical imaging techniques to measure changes in intracellular calcium, using the fluorescence of a calcium indicator dye within the cytosol.
                
  In skeletal muscle cells calcium ions are released in tiny packets from the sarcoplasmic reticulum. During small depolarizations of the membrane voltage, these calcium release events, or calcium "sparks", appear as brief elevations of calcium of about 100 nanomolar, lasting 10 milliseconds. These sparks are caused by the opening of individual (or a few) calcium release channels in the membrane of the sarcoplasmic reticulum. In addition to sparks activated by changes of membrane potential, we have also observed sparks caused by cytosolic calcium itself, activated by a mechanism known as calcium-induced calcium release. These studies will allow us to examine the activation of calcium release at the level of single release channels, so as to characterize the voltage and calcium dependence of channel activation in situ.

We are also interested in calcium signaling in cells with altered expression of the proteins involved in calcium transport, especially the calcium pump know as SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase).  In cardiac myocytes over-expression of exogenous isoforms of SERCA lead to dramatic changes in the waveform of the intracellular calcium signal.  Under-expression of SERCA, achieved using siRNA methods, leads to a dramatic re-organization of the proteins involved in calcium signaling and contractility of heart cells. We believe these studies will ultimately help in optimizing conditions for the treatment and amelioration of heart disease in patients using gene therapy.

Lab Personnel:
Shawn Mullen, Post-doc

Publications:
Klein MG and Schneider MF. 2005. Calcium sparks in skeletal muscle. Progress in Biophysics & Molecular Biology, In press.
            
Cavagna M, O'Donnell JM, Sumbilla C, Inesi G, and Klein MG. 2000. Exogenous Ca2+-ATPase isoform effects on Ca2+ transients of embryonic chicken and neonatal rat cardiacmyocytes. Journal of Physiol. 528:53-63.