Role of Ca2+/K+ ion exchange in intracellular storage and release of Ca2+.
Although fluctuations in cytosolic Ca2+ concentration have a crucial role in relaying intracellular messages in the cell, the dynamics of Ca2+ storage in and release from intracellular sequestering compartments remains poorly understood. The rapid release of stored Ca2+ requires large concentration gradients that had been thought to result from low-affinity buffering of Ca2+ by the polyanionic matrices within Ca2+-sequestering organelles. However, our results here show that resting luminal free Ca2+ concentration inside the endoplasmic reticulum and in the mucin granules remains at low levels (20-35 microM). But after stimulation, the free luminal [Ca2+] increases, undergoing large oscillations, leading to corresponding oscillations of Ca2+ release to the cytosol. These remarkable dynamics of luminal [Ca2+] result from a fast and highly cooperative Ca2+/K+ ion-exchange process rather than from Ca2+ transport into the lumen. This common paradigm for Ca2+ storage and release, found in two different Ca2+-sequestering organelles, requires the functional interaction of three molecular components: a polyanionic matrix that functions as a Ca2+/K+ ion exchanger, and two Ca2+-sensitive channels, one to import K+ into the Ca2+-sequestering compartments, the other to release Ca2+ to the cytosol.
Nguyen
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Department of Bioengineering, University of Washington, Seattle 98195, USA.
Chin
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Verdugo
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D002923:Cilia; D003594:Cytoplasmic Granules / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005089:Exocytosis; D020397:Goblet Cells / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007474:Ion Exchange; D009077:Mucins / Q000378:metabolism; D011188:Potassium / Q000737:chemistry / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D011817:Rabbits; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009077:Mucins; D015221:Potassium Channels; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium