pH Nanoenvironment at the Surface of Single Melanoma Cells

Abstract

Extracellular pH and the Na⁺/H⁺ exchanger (NHE1) modulate tumor cell migration. Yet, the pH nanoenvironment at the outer surface of the cell membrane (pH_em) where cell/matrix interaction occurs and matrix metalloproteinases work was never measured. We present a method to measure this pH nanoenvironment using proton-sensitive dyes to label the outer leaflet of the plasma membrane or the glycocalyx of human melanoma cells. Polarized cells generate an extracellular proton gradient at their surface that increases from the rear end to the leading edge of the lamellipodium along the direction of movement. This gradient collapses upon NHE1 inhibition by HOE642. NHE1 stimulation by intracellular acidification increases the difference in pH_em between the tips of lamellipodia and the cell body in a Na⁺ dependent way. Thus, cells create a pH nanoenvironment that promotes cell migration by facilitating cell adhesion at their front and the release of cell/matrix contacts at their rear part.

A biliary HCO3−umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

“…45,46 Our data might emphasize its putative beneficial action as a hepatocyte 47,48 and cholangiocyte 49,50 HCO À 3 secretagogue, particularly for small intrahepatic bile ductules affected in PBC. Our data may also explain, in part, the superiority of norUDCA above UDCA in the treatment of experimental cholangiopathy in Mdr2 À/À mice, a disease affecting also medium-and large-sized ducts, such as PSC 51 : Exogenous norUDCA has been shown to represent the strongest biliary HCO À earlier described for melanoma cells, 29 thus contributing to the biliary HCO À 3 umbrella to prohibit apolar hydrophobic bile acids from entering the cell. 7 A glycocalyx influences the permeation of charged proteins over the endothelial wall.…”

“…In melanoma cells, the pH measured in the glycocalyx was reported to be slightly higher than the pH of the medium, and the absolute number of H þ molecules differed up to 40% between different domains of the glycocalyx of a single cell. 29 HCO À 3 molecules are effectively trapped in the bile-acid-resistant 30 mucus gel layer of the gastric mucosa, thus establishing a local environment with a relatively high pH of $6-7 at the cell surface, whereas the bulk pH of gastric juice hovers around 1-2. [31][32][33] A similar function may be attributed to a glycocalyx of the biliary tree.…”

New insights into the physiological role of carbonic anhydrase IX in tumour pH regulation

“…Figure 2c illustrates an experiment in which the equilibrium between extracellular H þ , CO 2 and HCO 3 À was disturbed, providing substrate for CAIX catalysis. The pH at the extracellular surface of ca9-transfected cells of the HCT116 line was probed using a glycocalyx-binding pH dye (fluorescein-wheat germ agglutinin conjugate; Stock et al, 2007). Cells were bathed in pre-equilibrated 5% CO 2 /12mM HCO 3 À buffer at pH 7.2 and subjected to a brief 'ammonium prepulse' solution manoeuvre.…”

Effect of NHE1 antisense gene transfection on the biological behavior of SGC-7901 human gastric carcinoma cells

“…However, further studies are needed to determine whether or not the intervention of antisense NHE1 gene can decrease type 1 Na + /H + exchanger of membranous ion exchange protein in gastric carcinoma cells and reverse the malignant phenotypes. Therefore, in the present study, the purpose of transfection of antisense NHE1 gene into human gastric carcinoma cell line [19][20][21][22][23][24][25][26] . The enhancement of Na + -H + exchange by tumor cells, caused by increasing the quantitative distribution of NHE1 on the cell membrane, is the major molecular mechanism in the regulation of pH i in tumor cells.…”