Submitted on August 26, 2008
Revised on January 21, 2009
Accepted on January 21, 2009
Ca2+ pathway involved in the refilling of store sites in rat adrenal medullary cells
Hidetada Matsuoka1, Keita Harada1, Tomoya Ikeda1, Kouta Uetsuki1, Takeyoshi Sata1, Akira Warashina1, and Masumi Inoue1*
1 University of Occupational and Environmental Health School of Medicine
* To whom correspondence should be addressed. E-mail: minoue{at}med.uoeh-u.ac.jp.
It has been suggested that store-operated Ca2+ entry (SOC) facilitates catecholamine secretion and synthesis in bovine adrenal medullary (AM) cells. However, there has been no experimental result clearly showing that cation channel activity is enhanced by store Ca2+ depletion. Thus, the present experiments were undertaken to address the issue of whether or not rat AM cells have SOC channels. Inhibition of the sarco/endoplasmic reticulum Ca2+ (SERCA) pump resulted in a sustained increase in [Ca2+]i in rat AM cells. This increase was completely suppressed by 2 mM Ni2+, but not by 100 µM D600. A bath application of Ni2+, but not D600, produced an outward current at -60 mV in rat AM cells, whereas exposure to a SERCA pump inhibitor did not affect either the whole-cell current level or the Ni2+-induced outward current. The refilling of intracellular store sites was suppressed by the addition of Ni2+ ions to the perfusate. RT-PCR revealed that transcripts for TRPC1 and TRPC5 channels were present in rat adrenal medullae. Immunocytochemistry showed that TRPC1 channels, which have been implicated in SOC in certain types of cells, were mainly localized in the endoplasmic reticulum (ER) and not in the plasma membrane, and STIM1, a Ca2+ sensor in the ER, was not expressed in rat AM cells. Based on these results, we conclude that rat AM cells lack the SOC mechanism.
