LABORATORIES OF EDUARDO RIOS AND JINGSONG ZHOU
Section of Cellular Signaling
Department of Molecular Biophysics & Physiology
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Calcium Signaling
Multicellular organisms coordinate the activity of individual cells through signals that determine metabolic changes. Inside cells, signals are often transient changes in [Ca2+]. Our laboratories are part of the Section of Cellular Signaling, its member laboratories study these changes and try to understand their varied mechanisms and roles within healthy cells, as well as their alterations and failure modes in a number of diseases.
Calcium signals are ubiquitous and crucial. Excitation-contraction (E-C) coupling, the process that translates muscle membrane depolarization to increase in intracellular [Ca2+] and contraction, is the first recognized example of Ca signaling. Our group tries to understand E-C coupling at the molecular and cellular levels. These questions transcend muscle physiology; indeed, the concepts emerging from the muscle studies find general applicability, given the widespread distribution of Ca signaling in other types of muscle, nerve cells and other tissues. Recent technical and conceptual advances have allowed the field to agree on the basic aspects and mechanisms of signaling in healthy cells. Naturally, we are now trying to apply these advances to function in altered conditions, chiefly fatigue and disease.
Here we describe the general aims and approaches of our research. Readers who want to dig deeper, please view: "Key concepts", "Control of Ca inside the SR", "Research update (2012)" and "Artificial Ca sparks".
Approaches
are cellular and molecular.
Cellular methods include recording of calcium changes "globally" (that is, averaged over the whole cell) or locally, which is done by confocal microscopic imaging. The study of local events started in cardiac muscle with the discovery of Ca2+ sparks (Cheng et al. 1993), followed in skeletal muscle with our description of sparks: Tsugorka, Ríos and Blatter. Imaging elementary events of calcium release in skeletal muscle cells. Science 1995.
While they are local, sparks were soon found to involve multiple intracellular Ca channels. The animation is an early demonstration of the involvement of many channels. It shows a record of sparks that move along channel arrays of the Z disk as they evolve. The record spans 28 ms. From Brum et al. 2000.
Examples of studies of calcium signals at the local level: Launikonis et al. Depletion “skraps” and dynamic buffering inside the cellular calcium store. PNAS USA. 2006. Ríos et al. Calcium-dependent inactivation terminates calcium release in skeletal muscle of amphibians. J Gen Physiol. 2008.
The local studies are carried out in parallel with recording of global or "whole cell" signals. An early example was important to show species differences that can be ascribed to variation in the molecular makeup of the signaling apparatus: Shirokova, N., García, J., Pizarro, G. and Ríos, E. Ca2+ release from the sarcoplasmic reticulum compared in amphibian and mammalian skeletal muscle. J. Gen. Physiol, 1996. The differences at the global level were later matched with substantial differences at the local level (Shirokova, García and Ríos. Local Ca2+ release in mammalian skeletal muscle. J. Gen. Physiol. 1998.)
The definition of processes and mechanisms is often achieved through formal quantitative modeling. In 1997 we introduced the "couplon" as the functionally relevant multi-channel unit: Stern, Pizarro and Ríos. A local control model of excitation-contraction coupling in skeletal muscle. J. Gen. Physiol. 1997. The couplon concept was later extended to cardiac muscle. Stern et al. Local control models of cardiac excitation-contraction coupling. A possible role for allosteric interactions between ryanodine receptors. J. Gen. Physiol.1999.
Newer examples of work at the global level include The cell boundary theorem. A simple law of the control of calcium concentration. Rios, J. Physiol. Sci. 2010 and Evolution and modulation of intracellular calcium release during long-lasting, depleting depolarization in mouse muscle. Royer L, Pouvreau S, Ríos E. J Physiol. 2008
Molecular approaches include modifying the endowment of native proteins, or adding foreign ones, to then explore the functional consequences of these changes. An example: Pouvreau et al. Ca2+ sparks operated by membrane depolarization require isoform 3 ryanodine receptor channels in skeletal muscle. PNAS USA, 2007. This study demonstrated that the functional differences among species are due to the absence of a specific version of the Ca release channel (RyR3) in the muscle of mammals.
Inside the SR
A
recent focus of research in the lab is the development of techniques for
quantitatively imaging calcium concentration inside cellular organelles.
An early success was the development of the SEER technique. Launikonis et
al. Confocal imaging of [Ca2+] in cellular organelles by SEER, Shifted Excitation and Emission Ratioing of fluorescence. J Physiol, 2005. For current developments see
"Control of Ca inside the SR" .
The
molecular approaches and the advances in monitoring inside the SR rely on a technique (largely due to J. Vergara and M. DiFranco,
Protein Expr Purif. 2006) that allows expression of virtually any protein in muscles of adult
mice. A major advance in this direction
was the development of a novel biosensor, the fusion of the cameleon D4cpv and
the intra-SR protein calsequestrin, to image [Ca2+] inside the
sarcoplasmic reticulum. See
D4cpv-calsequestrin: a sensitive ratiometric biosensor accurately
targeted to the calcium store of skeletal muscle. Sztretye, M,
J Yi, L Figueroa, J Zhou, L Royer and 
a regulation described in cardiac muscle, both
mechanisms depend on the presence of calsequestrin in the SR.
Measurement
of RyR permeability reveals a role of calsequestrin in termination of SR Ca2+
release in skeletal muscle. Sztretye,
M, J Yi, L Figueroa, J Zhou, L Royer, P Allen, G Brum and
Artificial Ca sparks and CICR
An
advanced dual laser scanner, the 510 LIVE-Duo, from Zeiss Instruments, was used
to produce artificial Ca sparks in the cytosol of a cell, while simultaneously
imaging its cytosolic calcium concentration. In this way we could directly
probe the sensitivity to calcium of muscle cells. We found a striking
difference in this regard between amphibian (frog) cells, which respond to
artificial sparks with a propagating wave of calcium release, and mammalian
cells (which do not normally respond). For details and implications see Synthetic localized calcium transients directly probe signaling
mechanisms in skeletal muscle. Figueroa, L, V Shkryl, J Zhou, C
Manno, A Momotake, G
Contact us
Ms. Lucille Vaughn
Dept. Molecular Biophysics and Physiology
Section of Cellular Signaling,
Rush University School of Medicine
1750 W. Harrison St. Suite 1279JS
Chicago, IL 60612, USA
Office: 312-942-2081Â
Fax: 312-942-8711
Mail to: erios@rush.edu, lvaughn@rush.edu
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