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Trends Pharmacol Sci. 2004 Jan;25(1):8-15.

Organellar junctions promote targeted Ca2+ signaling in smooth muscle: why two membranes are better than one.

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The Department of Pharmacology & Therapeutics, The University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.


Numerous cellular processes are regulated by fluctuations in the concentration of a single cation, Ca(2+). To accomplish this feat, cells have developed mechanisms that target Ca(2+) signals to specific effectors in both space, by strategically localizing effectors and ion-transporting molecules, and time, by encoding the regulation of the frequency of Ca(2+) oscillations. With an emphasis on smooth muscle, we have analyzed how the interaction of Ca(2+) transporters located on closely apposing membranes of the plasma membrane, sarcoplasmic reticulum and mitochondria provides the structural foundation for site-specific and time-specific Ca(2+) signaling. These junctional membrane complexes can either control the concentration of Ca(2+) in the microdomain that surrounds an effector molecule or deliver Ca(2+) from the translocator on one membrane to a second translocator on the opposing membrane without significant diffusion into the bulk cytosol, an event we term 'linked Ca(2+) transport'.

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