The role of bicarbonate in regulatory volume decrease (RVD) in the epithelial-derived human breast cancer cell line ZR-75-1.

This study investigates the mechanisms involved in the regulatory volume decrease (RVD) in ZR-75-1 epithelial-derived human breast cancer cells. Cell volume changes were measured during osmotic shock using video imaging. In HEPES-buffered hypotonic solutions no RVD was observed; however, RVD was observed in HCO(3)(-)-buffered hypotonic solutions. Inhibition of RVD by 10 microM tamoxifen and 100 microM DIDS (inhibitors of volume-regulated anion channels; VRAC) and 2 mM TEA(+) (inhibitor of K(+) channels) indicates a role for these channels. In HCO(3)(-)-buffered Cl(-)-free solutions RVD was partially abolished indicating that HCO(3)(-) efflux can support RVD but also may have another role. Further experiments investigated whether HCO(3)(-) assists in the accumulation of Cl(-) via Cl(-)-HCO(3)(-) exchange. Regulatory volume increase (RVI) was also HCO(3)(-)-dependent and was inhibited by 500 microM DIDS and 10 microM 5-( N, N-dimethyl)-amiloride (DMA) indicating a role for coupled Cl(-)-HCO(3)(-) and Na(+)-H(+) exchange. Finally, in the presence of 10 microM DMA, RVD was partially inhibited providing further evidence for a role of Cl(-)-HCO(3)(-) exchange. Thus RVD in ZR-75-1 cells involves the activation of VRAC and K(+) channels. RVD is HCO(3)(-)-dependent and HCO(3)(-) efflux through VRAC appears to contribute directly to RVD. HCO(3)(-), however, also has another role in facilitating Cl(-) accumulation via Cl(-)-HCO(3)(-) exchange.