The secretory pathway Ca2+ ATPase (SPCA) provides the Golgi apparatus with a Ca2+ supply essential for Ca2+-dependent enzymes involved in the post-translational modification of proteins in transit through the secretory pathway. Ca2+ in the Golgi apparatus is also agonist-releasable and plays a role in hormone-induced Ca2+ transients. Although the Ca2+ ATPase inhibitors thapsigargin is more selective for the sarcoplasmic-endoplasmic reticulum Ca2+ ATPase (SERCA) than for SPCA, no inhibitor has been characterised that selectively inhibits SPCA. A number of inhibitors were assessed for their selectivity to the human SPCA1d compared to the more ubiquitous human SERCA2b. Each isoform was over-expressed in COS-7 cells and the Ca2+-dependent ATPase activity measured in their microsomal membranes. Both bis(2-hydroxy-3-tert-butyl-5-methylphenyl)methane(bis-phenol) and 2-aminoethoxydiphenylborate (2-APB) selectively inhibited SPCA1d (with IC50 values of 0.13 mu M and 0.18 mM, respectively), which were of 62- and 8.3-fold greater potency than the values for hSERCA2b (IC50 values; 8.1 mu M and 1.5 mM, respectively). Other inhibitors tested such as bis-phenol-A, tetrabromobisphenol-A and trifluoperazine inhibited both Ca2+ ATPases similarly. Furthermore, bis-phenol was able to mobilize Ca2+ in cells that had been pre-treated with thapsigargin. Therefore we conclude that given the potency and selectivity of bis-phenol it may prove a valuable tool in further understanding the role of SPCA in cellular processes. (C) 2012 Elsevier Inc. All rights reserved.