HISTAMINE-INDUCED CL- SECRETION IN HUMAN NASAL EPITHELIUM - RESPONSES OF APICAL AND BASOLATERAL MEMBRANES

The mechanism by which receptors coupled to phospholipase C (PLC) induce Cl- secretion in amiloride-pretreated cultures of human nasal epithelial (HNE) cultures was investigated. Histamine (10(-4) M, basolateral administration) stimulated a rapid increase in equivalent short-circuit current, an index of Cl- secretion, that returned to baseline within 5 min. Intracellular recordings with double-barreled Cl--selective microelectrodes showed that the apical and basolateral membrane potentials rapidly hyperpolarized, the fractional resistance of the apical membrane increased, and the transepithelial resistance decreased in response to histamine. Intracellular Cl- activity remained constant. Equivalent circuit analysis revealed that the early portion (<0.9 min) of the Cl- secretory response was driven by an activation of a hyperpolarizing basolateral conductance, likely K+, whereas the later (>0.9 min) phase of Cl- secretion reflects activation of the apical membrane Cl- conductance. Histamine raised intracellular Ca2+ (Ca(i)2+) measured by fura-2 in HNE with a potency similar to that observed for induction of Cl- secretion. Both intracellular release and plasma membrane influx pathways were identified, typical of receptor-mediated activation of PLC. The intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (15 muM), coupled with reduced bathing solution Ca2+, blunted the rise in Ca(i)2+ and the net transepithelial Cl- secretory response to histamine. We conclude that 1) histamine induced Cl- secretion in HNE by a sequential mechanism: the rapid initial component reflects activation of the basolateral K+ conductance, and the later component reflects activation of an apical Cl- conductance; and 2) the level of Ca(i)2+ may participate in the activation of both the basolateral and apical conductances.