LU52396, an inhibitor of the store-dependent (capacitative) Ca2+ influx

The effects of 1-[2-(4-fluorophenyl)cyclohexyl]-2-[4-(3-phenylalkyl)-piperazin-1-yl]-et hanol, LU52396, on a) Ca²⁺ influx across the plasma membrane and b) Ca²⁺ mobilization from intracellular rapidly-exchanging Ca²⁺ stores were investigated in HeLa cells and in isolated microsomal fractions derived from the cerebellum and the skeletal muscle. LU52396 was found to be a potent inhibitor (K_i of about 2 μM) of the Ca²⁺ influx activated by depletion of intracellular Ca²⁺ stores, a phenomenon referred to as store-dependent or capacitative Ca²⁺ influx. Such an effect, which was reversed by cell washing, was mediated neither by a depolarization of the cell, with decrease in the driving force for cation influx, nor by a change of the intracellular pH, and might therefore be due to a direct action of the drug on either the responsible channel in the plasma membrane or, less likely, on its regulatory mechanisms. Additional effects, i.e. inhibition of receptor-mediated Ca²⁺ influx, of Ca²⁺ release from intracellular stores via either inositol 1,4,5-trisphosphate or ryanodine receptors, and Ca²⁺ reuptake into the stores via sarcoplasmic-endoplasmic reticulum Ca²⁺-ATPases, were also induced by the drug, however at concentrations 20-fold or more than those effective on the store-dependent influx. To our knowledge LU52396 is the first pharmacological tool that is found to be addressed with some preference to the store-dependent Ca²⁺ influx. It promises, therefore, to be useful for the characterization of the process, the identification of the responsible channels and, possibly, also of the molecular mechanisms through which these channels operate.