Calcium-Sensing Receptor Stimulation Induces Nonselective Cation Channel Activation in Breast Cancer Cells

Abstract

The calcium-sensing receptor (CaR) is expressed in epithelial ducts of both normal human breast and breast cancer tissue, as well as in the MCF-7 cell line as assessed by immunohistochemistry and Western blot analysis. However, to date, there are no data regarding the transduction pathways of CaR in breast cancer cells. In this study, we show that a CaR agonist, spermine, and increased extracellular Ca²⁺ ([Ca²⁺]_o) sequentially activate two inward currents at –80 mV. The first was highly permeable to Ca²⁺ and inhibited by 2-aminophenyl borate (2-APB). In contrast, the second was more sensitive to Na⁺ and Li⁺ than to Ca²⁺ and insensitive to 2-APB. Furthermore, intracellular dialysis with high Mg²⁺, flufenamic acid or amiloride perfusion was without any effect on the second current. Both currents were inhibited by La³⁺. Calcium imaging recordings showed that both [Ca²⁺]_o and spermine induced an increase in intracellular calcium ([Ca²⁺]_i) and that removal of extracellular Ca²⁺ or perfusion of 2-APB caused a decline in [Ca²⁺]_i. It is well known that stimulation of CaR by an increase in [Ca²⁺]_o or with spermine is associated with activation of phospholipase C (PLC). Inhibition of PLC reduced the [Ca²⁺]_o-stimulated [Ca²⁺]_i increase. Lastly, reverse-transcriptase polymerase chain reaction showed that MCF-7 cells expressed canonical transient receptor potential (TRPCs) channels. Our results suggest that, in MCF-7 cells, CaR is functionally coupled to Ca²⁺-permeable cationic TRPCs, for which TRPC1 and TRPC6 are the most likely candidates for the highly selective Ca²⁺ current. Moreover, the pharmacology of the second Na⁺ current excludes the involvement of the more selective Na⁺ transient receptor potential melastatin (TRPM4 and TRPM5) and the classical epithelial Na⁺ channels.