Basolateral store-operated Ca2+-entry in polarized human bronchial and colonic epithelial cells

Bronchial epithelial cells respond to extracellular nucleotides from the lu minal and basolateral side activating Cl- secretion via [Ca2+](i) increase. In this study we investigated the differences of apically (ap) and basolat erally (bl) stimulated[Ca2+](i) signals in polarized human bronchial epithe lial cells (16HBE14o(-)). Specifically we investigated the localization of 'capacitative Ca2+ entry' (CCE). 16HBE14o(-) cells grown on permeable filte rs were mounted into an Ussing chamber built for the simultaneous measureme nt of Fura-2 fluorescence and electrical properties. Application of ATP fro m both sides induced a rapid [Ca2+](i) increase and subsequent sustained [C a2+](i) plateau due to transmembraneous Ca2+-influx. The use of different n ucleotides revealed the following rank order or potency which was very simi lar for addition from the apical or basolateral side: UTP (EC50 ap: 4 mu M, bl: 5 mu M) > ATP (EC50 ap: 4 mu M, bl: 10 mu M) > ADP (n=4-7 from both si des). 2-MeS-ATP, AMP, adenosine and py-methylene ATP were ineffective (n=3 from both sides). The ATP- (ap and bl) induced Ca2+ influx was only abolish ed by removal of basolateral Ca2+. This was also true for receptor-independ ent activation of Ca2+-influx by intracellular Ca2+-store depletion with 2, 5 Di-(tert-butyl)1,4-benzohydroquinone (BHQ) (10 mu M). Also in polarized T 84 cells the basolateral carbachol and BHQ activated Ca2+ plateau was exclu sively sensitive to removal of basolateral Ca2+. We propose that in all pol arized epithelial cells the CCE entry pathway is located in the basolateral membrane. We furthermore suggest that [Ca2+](i) elevating agonists acting from the apical side of the epithelium lead to the opening of a basolateral CCE pathway. (C) Harcourt Publishers Ltd 1999.