investigator's application): Large and often repetitive increases of cytosolic [Ca2+] ([Ca2+]c) mediate the effects of various hormones that act through the second messenger inositol 1,4,5-triphosphate (IP3) in many cell types. Elevated [Ca2+]c results in activation of Ca2+-sensitive components that participate in a wide range of cellular functions. Full activation of a particular target would be evoked by prolonged Ca2+ increases, however, simultaneous full activation of various targets in the cells by permanently high [Ca2+] could lead to cell injury. The physiological range of stimulation appears to be restricted to the transient [Ca2+]c increases and in many cases the intensity of hormonal stimulation is converted into the frequency of brief and uniform [Ca2+]c increases (frequency modulation). It is well established that the bursting phase of Ca2+ mobilization occurs when IP3 opens Ca2+ release channels on the endoplasmic reticulum Ca2+ store using positive feed back effects exerted by the released Ca2+. However, little is known about the mechanism of the falling phase of Ca2+ transients. The present proposal is directed towards elucidating the mechanisms that are responsible for the deactivation of [Ca2+]c transients using hepatocytes and endocrine cells of the adrenals as a model system. The investigators suggest, that IP3-induced (time dependent) inactivation of the IP3 receptor (IP3R) is an important factor in the falling phase of [Ca2+]c transients. It is hypothesized that inactivation of the IP3R is particularly large if IP3R is activated by IP3 in Ca2+-sensitized state that may occur at modest increases of IP3 evoked by physiological levels of hormones. The investigators also suggest that Ca2+ released by IP3 is transiently accumulated in mitochondria, allowing mitochondria to contribute to the decay of [Ca2+]c transients and subsequently to recharge IP3 sensitive Ca2+ stores. The investigators propose that mitochondria are not only an important target of the cytosolic Ca2+ signal, but also represent a Ca2+ store that controls the ability of the endoplasmic reticulum Ca2+ store to generate [Ca2+]c transients. A major component of these studies will rely on imaging approaches to measure dynamics of Ca2+ movements within both intact and permeabilized cells, including some novel techniques that permit studies of IP3 action at the level of the Ca2+ stores. Imaging methods will be used in combination with electrophysiology and molecular biology.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29DK051526-02
Application #
2458939
Study Section
Physiology Study Section (PHY)
Program Officer
Sato, Sheryl M
Project Start
1996-08-20
Project End
2001-07-31
Budget Start
1997-08-01
Budget End
1998-07-31
Support Year
2
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Thomas Jefferson University
Department
Pathology
Type
Schools of Medicine
DUNS #
061197161
City
Philadelphia
State
PA
Country
United States
Zip Code
19107
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Csordas, Gyorgy; Varnai, Peter; Golenar, Tunde et al. (2012) Calcium transport across the inner mitochondrial membrane: molecular mechanisms and pharmacology. Mol Cell Endocrinol 353:109-13

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