Personal History:Harvard University, B.A., 1970, (Biochemistry, magna cum laude) Yale University, Ph.D. 1975 (Physiology, R.W. Tsien, advisor) Yale University, M.D. 1976 Internship in Medicine, University of Washington, Seattle, WA, 1976-1977, (Dr. Robert Petersdorf, Chairman of Medicine) British-American Heart fellowship, Oxford University, Oxford, England, 1977-1979, (Dr. Denis Noble), 1979-present, University of Maryland, 1995-present, University of Maryland Biotechnology Center.
Work in the lab focuses on Ca2+ signaling in living cells. By combining confocal, two photon or wide-field microscopy with whole cell patch clamp techniques, we have been able to investigate the effects of subcellular and intracellular Ca2+ concentration ([Ca2+]i on cellular function. Diverse additional tools are used as needed including flash photolysis of caged chemicals, multi-photon uncaging, single channel examination in planar lipid bilayers and by patch clamp, immuno-fluorescence imaging, use of cells from transgenic and gene knockout animals, and use of primary cultures and co-cultures. There are five areas of active work.
Cellular and Molecular Ca2+ Signaling.
Local Ca2+ signals depend on the subcellular organization of the affected cells. Ryanodine receptors (RyRs) and IP3 receptors (IP3Rs), intracellular Ca2+ release channels with large conductances that are found in the sarcoplasmic reticulum (SR) and in the endoplasmic reticulum of many cells, are opened by an increase in [Ca2+]i . This local increase in [Ca2+]i may come from Ca2+ channels on the plasmalemmal membrane, the Na+/ Ca2+ exchanger bringing Ca2+ into the cell, non-selective or poorly selective cation channels, or other intracellular Ca2+ release channels. Recently we have identified a new source of such activator Ca2+: Na+ channels whose selectivity is transiently modified. Specific activators and kinases modulate both the sources of Ca2+ influx and the RyRs and IP3Rs. In many cells, there are subcellular regions in which Ca2+ -conducting channels, RyRs, and IP3Rs are co-localized, permitting amplification of a very small signal through the Ca2+ -conducting channels.
In heart cells, Ca2+ sparks reflect the Ca2+ -dependent activation of RyRs. Ca2+ sparks are the elementary events in excitation-contraction coupling. The activation of Ca2+ sparks by the L-type Ca2+ channel current (and more recently Ca2+ flux through Na+ channels) underlies normal contraction. Under pathologic conditions, arrhythmias can occur due to the untowards activation of Ca2+ sparks. In heart failure, the inadequate activation of Ca2+ sparks can explain, in part, the pathology. Current work is examining how SR Ca2+ release is activated and how it is terminated.
Smooth Muscle Cells
Arterial smooth muscle contains Ca2+ -activated potassium channels and both RyRs and IP3Rs. The activation of Ca2+ sparks in such smooth muscle (due to the opening of RyRs) activates the Kca channels and leads to hyperpolarization of the smooth muscle. By this means, an increase in local [Ca2+]i activates cell-wide relaxation. Much of this work was carried out using vascular smooth muscle from brain arteries. Similar results, however, occur in the coronary arteries. Current work examines how Ca2+ sparks are modulated in smooth muscle and how IP3Rs interact with RyRs.
Skeletal Muscle Cells
Since voltage-gated SR Ca2+ release occurs in mammalian skeletal muscle, it was surprising that we could observe Ca2+ sparks in these cells due to two processes. We observed Ca2+ sparks activated directly by depolarization and we observed Ca2+ sparks activated by a local increase in [Ca2+]i. Current work examines how the local [Ca2+] signals change with development and how the developmental regulation of the transverse tubules affects Ca2+ signaling.
[Ca2+]i signals in neurons appears to be more restricted in size than in muscle. Furthermore, there appears to be a larger role played by the IP3Rs. The more diverse kinds of Ca2+ channels available, the additional sources of Ca2+ influx and efflux contribute to the complex regulation of local [Ca2+]i signals in neurons. Additionally, the role of local [Ca2+]i signals in influencing both pre-synaptic and post-synaptic signaling are being studied. Work has centered on an examination of DRG neurons, on cerebellar Purkinje cells and on other CNS neurons that display Ca2+ -induced Ca2+ -release.
Nelson, M.T., Cheng, H., Rubart, M., Santana, L.F., Bonev, A., Knot, H. and Lederer, W.J. (1995). Relaxation of arterial smooth muscle by calcium sparks. Science 270:633-637.