EPITHELIAL cells exist in a complex setting in which responses to mucosal or serosal environments are mediated by receptors expressed on specialized cellular domains, such as apical versus basolateral cell membranes, We investigated whether airway epithelia can react selectively through G-protein-coupled receptors to stimuli in the mucosal or serosal environments by measuring inositol phosphate and intracellular Ca2+ responses in polarized human nasal epithelial monolayers, We report here that unilateral ATP (10(-4) M) administration stimulated P-2 purinoceptors and tapped pools of intracellular Ca2+ associated with the plasma membrane ipsilateral but not contralateral to stimulated receptors. Similarly, activation of plasma membrane Ca2+ influx by ATP was confined to the membrane ipsilateral to receptor stimulation. These findings demonstrate that polarized epithelia restrict P-2 receptor-mediated responses to a single domain of the cell, reflecting membrane-specific generation and catabolism of inositol phosphates and confinement of calcium influx regulation to the membrane ipsilateral to the stimulated receptors.