Purinergic agonists, but not cAMP, stimulate coupled granule fusion and Cl- conductance in HT29-Cl.16E.

Cl- conductance and capacitance were simultaneously measured in the mucin-secreting cell line, HT29-Cl.16E (Cl.16E), and its sister cell line, HT29-Cl.19A (Cl.19A), which lacks mucin granules. Purinergic stimulation by extracellular ATP transiently increased Cl- conductance in both cell lines with similar peak increases of 0.92 and 1.00 nS/pF in Cl.16E and Cl.19A cells, respectively (baseline of 0.08 nS/pF). Cell capacitance increased only in Cl.16E cells (17% above baseline of 22 pF in Cl.16E and 1% above baseline of 18 pF in Cl.19A cells). Wortmannin inhibited the purinergically activated Cl- conductance and capacitance increases in Cl.16E by 50 and 80%, respectively, but had no effects in Cl.19A cells. In Cl.16E cells, adenosine 3',5'-cyclic monophosphate (cAMP) signaling increased Cl- conductance from 0.08 to 0.52 nS/pF without changing capacitance. Cl- secretion in Cl.16E monolayers was additive in response to supramaximal stimulation of purinergic receptors and adenylyl cyclase, even though granule fusion is nine times greater with purinergic than adenylyl cyclase stimulation. In conclusion, 1) wortmannin does not directly inhibit activation of Cl- conductance, 2) at least 50% of purinergically activated Cl- conductance in Cl.16E is associated with granule fusion, and 3) cAMP-activated Cl- conductance is not associated with granules.