ATP-activated basolateral Na+/H+ exchange in human normal and cystic fibrosis airway epithelium

This study investigated the distribution (apical/basolateral membrane) of Na+/H+ exchange in human nasal epithelial cell monolayers from cystic fibrosis (CF) and non-CF individuals. Monolayers of non-CF and CF preparations were loaded with the pH probe 2',7'-bis(carboxyethyl)-5(6)- carboxyfluorescein, and intracellular pH (pH1) was measured with a microfluorimeter. In nominally HCO3(-)-free NaCl Ringer solution, basal pHi values in non-CF and CF monolayers were essentially identical (approximately 7.1). When cells were acid loaded (NH4+ prepulse), subsequent alkalinization of non-CF and CF cell monolayers required serosal Na+ and was blocked by serosal, but not mucosal, amiloride (500 microM). In the presence of extracellular Na+, initial rates (delta pHi/min) of recovery from an acid load in non-CF and CF preparations were statistically identical (approximately 0.08). Pretreatment of monolayers with ATP (100 microM) or phorbol 12-myristate 13-acetate (PMA; 100 nM) caused initial rates of recovery to increase by twofold over control values in both preparations. These data provide evidence in support for an ATP- and PMA-activated Na+/H+ exchanger located at the basolateral surface of airway epithelia.