Amiloride inhibits macropinocytosis by lowering submembranous pH and preventing Rac1 and Cdc42 signaling.
Macropinocytosis is differentiated from other types of endocytosis by its unique susceptibility to inhibitors of Na(+)/H(+) exchange. Yet, the functional relationship between Na(+)/H(+) exchange and macropinosome formation remains obscure. In A431 cells, stimulation by EGF simultaneously activated macropinocytosis and Na(+)/H(+) exchange, elevating cytosolic pH and stimulating Na(+) influx. Remarkably, although inhibition of Na(+)/H(+) exchange by amiloride or HOE-694 obliterated macropinocytosis, neither cytosolic alkalinization nor Na(+) influx were required. Instead, using novel probes of submembranous pH, we detected the accumulation of metabolically generated acid at sites of macropinocytosis, an effect counteracted by Na(+)/H(+) exchange and greatly magnified when amiloride or HOE-694 were present. The acidification observed in the presence of the inhibitors did not alter receptor engagement or phosphorylation, nor did it significantly depress phosphatidylinositol-3-kinase stimulation. However, activation of the GTPases that promote actin remodelling was found to be exquisitely sensitive to the submembranous pH. This sensitivity confers to macropinocytosis its unique susceptibility to inhibitors of Na(+)/H(+) exchange.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.