Role of Ca2+/K+ ion exchange in intracellular storage and release of Ca2+

Thien Nguyen, Wei-Chun Chin and Pedro Verdugo ()
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Thien Nguyen: University of Washington
Wei-Chun Chin: University of Washington
Pedro Verdugo: University of Washington

Nature, 1998, vol. 395, issue 6705, 908-912

Abstract: Abstract Although fluctuations in cytosolic Ca2+ concentration have a crucial role in relaying intracellular messages in the cell1, 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 organelles2. 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 μM). 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.

Date: 1998
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DOI: 10.1038/27686

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