Heterogeneous responses of cell Ca2+ in human airway epithelium

The Ca(2+)-mobilizing actions of adenosine 5'-triphosphate (ATP), bradykinin, and histamine were compared in phenotypically distinct human nasal epithelial (HNE) cell types and as a function of time in cell culture. Single-cell measurements of intracellular free Ca2+ (Ca2+i, Fura-2 fluorescence) were recorded in ciliated cells 1-2 days in primary culture, and in nonciliated cells 1-2 days (keratin 14-positive) or 4-5 days (keratin 18-positive) after seeding. No difference in basal Ca2+i was noted between ciliated and nonciliated cell preparations. For ciliated and nonciliated cells studied 1-2 days in culture, ATP, bradykinin, and histamine elicited a cytosolic Ca2+ response in 100% of the cells examined. For nonciliated HNE cells maintained 4-5 days in culture, ATP (10(-4) M) increased cytosolic Ca2+ in all cells tested, but only 85% of the cells responded to bradykinin (10(-5) M) addition, and 65% to histamine (10(-4) M) stimulation. In terms of the absolute change of Ca2+i (delta Ca2+i, peak-basal value), the efficacy was ATP > bradykinin > histamine for the 3 HNE cell preparations. However, the delta Ca2+i in response to agonists was smaller in nonciliated HNE cells studied 1-2 days or 4-5 days in culture as compared to the ciliated cell preparation. Thapsigargin (300 nM), an agent that mobilizes Ca2+i, was equally effective in raising cytosolic Ca2+ in nonciliated (1-2 days and 4-5 days in culture) and ciliated HNE cells. These data show that ciliated cells consistently respond to all agonists, whereas the cytosolic Ca2+ response to ATP, bradykinin, and histamine in nonciliated cells was quantitatively reduced at a comparable time period (1-2 days) and became smaller and less frequent in nonciliated cell preparations maintained 4-5 days in culture. These results demonstrate time-dependent differences in the magnitude and frequency of cytosolic Ca2+ responses to certain agonists, strongly indicating that measurements of Ca2+i in HNE cells must account for the heterogeneity of the cell types and the time cells are maintained in primary culture.