Sodium regulates PLC and IP R-mediated calcium signaling in invasive breast cancer cells.

Intracellular Ca signaling and Na homeostasis are inextricably linked via ion channels and co-transporters, with alterations in the concentration of one ion having profound effects on the other. Evidence indicates that intracellular Na concentration ([Na ] ) is elevated in breast tumors, and that aberrant Ca signaling regulates numerous key cancer hallmark processes. The present study therefore aimed to determine the effects of Na depletion on intracellular Ca handling in metastatic breast cancer cell lines. The relationship between Na and Ca was probed using fura-2 and SBFI fluorescence imaging and replacement of extracellular Na with equimolar N-methyl-D-glucamine (0Na /NMDG) or choline chloride (0Na /ChoCl). In triple-negative MDA-MB-231 and MDA-MB-468 cells and Her2+ SKBR3 cells, but not ER+ MCF-7 cells, 0Na /NMDG and 0Na /ChoCl resulted in a slow, sustained depletion in [Na ] that was accompanied by a rapid and sustained increase in intracellular Ca concentration ([Ca ] ). Application of La in nominal Ca -free conditions had no effect on this response, ruling out reverse-mode NCX activity and Ca entry channels. Moreover, the Na -linked [Ca ] increase was independent of membrane potential hyperpolarization (NS-1619), but was inhibited by pharmacological blockade of IP receptors (2-APB), phospholipase C (PLC, U73122) or following depletion of endoplasmic reticulum Ca stores (cyclopiazonic acid). Thus, Na is linked to PLC/IP -mediated activation of endoplasmic reticulum Ca release in metastatic breast cancer cells and this may have an important role in breast tumors where [Na ] is perturbed.