Normoxic cells remotely regulate the acid-base balance of cells at the hypoxic core of connexin-coupled tumor growths

Abstract

ATP fuels the removal of metabolic end-products, including H + ions that profoundly modulate biological activities. Energetic resources in hypoxic tumor regions are constrained by low-yielding glycolysis, and any means of reducing the cost of acid extrusion, without compromising pH homeostasis, would therefore be advantageous for cancer cells. Some cancers express connexin channels that allow solute exchange between cells, and we propose that, via this route, normoxic cells supply hypoxic neighbors with acid-neutralizing HCO 3 - ions. This hypothesis was tested by imaging cytoplasmic pH in spheroidal tissue growths of connexin43-positive pancreatic cancer Colo357 cells during light-controlled H + uncaging at the hypoxic core. Cytoplasmic acid retention at the core was halved in the presence of CO 2 /HCO 3 - , but this process requires a restorative HCO 3 - flux. The effect of CO 2 /HCO 3 - was ablated by connexin43 inhibition or knockdown. In connexin-decoupled spheroids, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), an inhibitor of HCO 3 - uptake, had no effect on cytoplasmic [H + ] in the H + -uncaging region, indicating that DIDS-sensitive transport is not an adequate pH-regulatory strategy therein. With intact connexin-coupling, acid retention at the core increased upon DIDS treatment, indicating that HCO 3 - ions are taken up actively by peripheral cells and then transmitted passively to cells at the hypoxic core. Thus, the energetic burden of pH regulation is…