Cholinergic stimulation produces oscillations of cytosolic Ca²⁺ in a secretory epithelial cell line, T84

The effects of carbamylcholine (carbachol) on intracellular Ca²⁺ concentration ([Ca²⁺](c)) of T84 cells were examined using the fluorescent Ca²⁺ indicator fura-2 and microfluorometric techniques. In single isolated cells, carbachol (100 μM) caused a rapid increase in [Ca²⁺](c) of 184 ± 15 nM (SE, n = 44) from a resting value of 56 ± 7 nM. This initial transient was followed by a series of oscillations in 68% of the cells. Atropine (10 μM) blocked this response. Removal of bath Ca²⁺ did not inhibit the rise in [Ca²⁺](c) or oscillations, but the response duration was shortened in 47% of the cells. The amplitude and latency of the initial Ca²⁺ rise, frequency of oscillations, and number of responding cells varied with the agonist concentration. We have previously shown that carbachol induces an oscillating K⁺ conductance in T84 cells [D. evor, S. Simasko, and M. Duffey. Am. J. Physiol. 258 (Cell Physiol. 27): C318-C326, 1990]. Simultaneous measurement of membrane K⁺ current and fura-2 fluorescence in the same cell demonstrated a correlation between the rise in [Ca²⁺](c) and increase in K⁺ current. These results show that a rise in [Ca²⁺](c) and oscillations is likely to underlie the membrane K⁺ current responses to carbachol in T84 cells. Responses from a single cell within a subconfluent monolayer were different from those of isolated cells. In cells of a monolayer the initial [Ca²⁺](c) rise (111 ± 8 nM; n = 41) was followed by a decline to a stable plateau, and oscillations were not seen. Removal of bath Ca²⁺ both reduced the initial transient and eliminated the plateau phase of the response. These results suggest that cell-to-cell contact or differentiation during monolayer formation influences the Ca²⁺ handling mechanisms of T84 cells.