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¹ Department of Physiology and Biophysics University of Washington School of Medicine, Seattle, WA 98195
² National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing 100100, China

Correspondence to Bertil Hille: hille{at}u.washington.edu

Many studies of Ca²⁺ signaling use PC12 cells, yet the balance of Ca²⁺ clearance mechanisms in these cells is unknown. We used pharmacological inhibition of Ca²⁺ transporters to characterize Ca²⁺ clearance after depolarizations in both undifferentiated and nerve growth factor-differentiated PC12 cells. Sarco-endoplasmic reticulum Ca²⁺ ATPase (SERCA), plasma membrane Ca²⁺ ATPase (PMCA), and Na⁺/Ca²⁺ exchanger (NCX) account for almost all Ca²⁺ clearance in both cell states, with NCX and PMCA making the greatest contributions. Any contribution of mitochondrial uniporters is small. The ATP pool in differentiated cells was much more labile than that of undifferentiated cells in the presence of agents that dissipated mitochondrial proton gradients. Differentiated PC12 cells have a small component of Ca²⁺ clearance possessing pharmacological characteristics consistent with secretory pathway Ca²⁺ ATPase (SPCA), potentially residing on Golgi and/or secretory granules. Undifferentiated and differentiated cells are similar in overall Ca²⁺ transport and in the small transport due to SERCA, but they differ in the fraction of transport by PMCA and NCX. Transport in neurites of differentiated PC12 cells was qualitatively similar to that in the somata, except that the ER stores in neurites sometimes released Ca²⁺ instead of clearing it after depolarization. We formulated a mathematical model to simulate the observed Ca²⁺ clearance and to describe the differences between these undifferentiated and NGF-differentiated states quantitatively. The model required a value for the endogenous Ca²⁺ binding ratio of PC12 cell cytoplasm, which we measured to be 268 ± 85. Our results indicate that Ca²⁺ transport in undifferentiated PC12 cells is quite unlike transport in adrenal chromaffin cells, for which they often are considered models. Transport in both cell states more closely resembles that of sympathetic neurons, for which differentiated PC12 cells often are considered models. Comparison with other cell types shows that different cells emphasize different Ca²⁺ transport mechanisms.

Abbreviations used in this paper: BHQ, tert-butylhydroquinone; GPN, glycyl phenylalanyl β-napthylamide; MtU, mitochondrial Ca²⁺ uniporter; NCX, Na⁺-Ca²⁺ exchanger; NGF, nerve growth factor; PMCA, plasma membrane Ca²⁺ ATPase; SERCA, sarcoplasmic endoplasmic reticulum Ca²⁺ ATPase; SPCA, secretory pathway Ca²⁺ ATPase; TG, thapsigargin.

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This article has been cited by other articles:

				J. G. Duman, L. Chen, and B. Hille Calcium Transport Mechanisms of PC12 Cells J. Cell Biol., April 21, 2008; 181(2): i9 - i9. [Full Text]

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