Relation of anion secretory activity to intracellular Ca2+ in response to lysylbradykinin and histamine in a cultured human colonic epithelium.

A cultured human epithelial cell line, Colony 29, has been used to investigate the relation between anion secretion and intracellular Ca2+ concentration (Cai) in response to the secretagogues, lysylbradykinin (LBk) and histamine. Anion secretion was measured as short-circuit current (SCC) responses in epithelia cultured on previous supports. Cai was measured both in cell suspensions and epithelial monolayers using Fura-2 fluorescence. While it is concluded that raised Cai is responsible for anion secretion the relationship is complex. For both secretagogues there is a receptor reserve, that is the maximal Cai increase is greater than that required to cause a maximal secretory response. By examining the interactions between maximally effective concentrations of LBk and histamine it was shown that neither the SCC nor Cai responses behaved additively. From observations in the absence of external Ca2+ it was concluded that both secretagogues cause Ca2+ release from the same intracellular source, but that in normal conditions Ca2+ derived from intracellular and extracellular sources is responsible for the full effect.