Pharmacological modulation of monovalent cation currents through the epithelial Ca2+ channel ECaC1

1 The recent identification of the epithelial Ca2+ channel, ECaCl, represents a major step forward in our knowledge of renal Ca2+ handling. ECaCl constitutes the rate-limiting apical Ca2+ entry mechanism of active, transcellular Ca2+ reabsorption. This unique highly selective Ca2+ channel shares a low but significant homology with transient receptor potential (TRP) channels and vanilloid receptors (VR). 2 We have studied the pharmacological modulation of currents through ECaCl heterologously expressed in HEK 293 cells. Monovalent cation currents were measured by use of the whole cell patch clamp technique in cells dialysed with 10 mm BAPTA or 10 mm EGTA to prevent the fast Ca2+ dependent inactivation of ECaCl. 3 Several modulators were tested, including inorganic cations, putative store-operated Ca2+ entry (SOC) blockers, the vanilloid receptor (VR-1) blocker capsazepine, protein tyrosine kinase blockers, calmodulin antagonists and ruthenium red. 4 Ruthenium red and econazole appeared to be the most effective inhibitors of currents through ECaCl, with IC50 values of 111 nm and 1.3 muM, respectively, whereas the selective SOC inhibitor, SKF96365, was nearly ineffective. 5 The divalent cation current block profile for ECaCl is Pb2+ = CU2+ > Zn2+ > Co2+ > Fe2+. with IC50 values between 1 and approximately 10 muM. 6 In conclusion, ECaC activity is effectively inhibited by various compounds including ruthenium red, antimycotic drugs and divalent cations, which might be useful tools for pharmacological manipulation and several disorders related to Ca2+ homeostasis could benefit from such developments.