Transepithelial Ion Transport in Cultured Colonic Epithelial Cell Monolayers

Cyclic AMP and Ca2+ interactions affecting epithelial chloride secretion in human cultured colonic epithelia

“…Similarly total charge transfer, measured as area under the response curve for 8 min, was used to examine potentiation of LBK by vasoactive intestinal polypeptide (VIP). Like forskolin, this agent increases cyclic AMP content and activates adenylate cyclase in HCA-7 monolayers (Cuthbert, 1990b). Low concentrations of VIP (1O nM) caused significant potentiation of the responses to LBK, applied either to the apical or basolateral surface ( Figure 3).…”

“…Epithelial monolayers grown from two mutant cell lines related to HCA-7, namely Colony 3 and Colony 29, were used to explore the type of potentiation seen with HCA-7 cells. Colony 3 monolayers show little or no response to forskolin as far as chloride secretion is concerned, yet they accumulate cyclic AMP to a much greater extent than HCA-7 monolayers (Cuthbert, 1990b). They do not respond to LBK but do to CCh and A23187.…”

“…The responses to LBK in Colony 29 cells are severely attenuated by cyclooxygenase inhibition with piroxicam. As with Colony 3 monolayers, forskolin caused a major accumulation of cyclic AMP, significantly greater than with HCA-7 (Cuthbert, 1990b). Figure 5 illustrates a series of paired experiments in which LBK (0.…”

“…Colony 29 monolayers have properties in some ways intermediate between HCA-7 and Colony 3. For example, SCC responses to forskolin, 1O LM, are in the ratio 6.2:1.2:1.0 for HCA-7, Colony 3 and Colony 29 respectively (Cuthbert, 1990b). As the responses in the last two are not maintained, the ratios are even more extreme when charge transfer is Where F, Pir and PG are shown it indicates that tissues were exposed to forskolin, 10 tvM; piroxicam, 5 ILM, and prostaglandin E2, 1O LM respectively for 5 min before responses to LBK were measured.…”

“…As the phenotypic characteristics are very different in these cell lines the mutants may provide starting points for molecular genetic studies to characterize the transport proteins uniquely encoded by structural genes. The non-additive responses observed relate to a particular type of pairing, that is the interaction between agents known to raise intracellular Ca2 , such as LBK and CCh and agents which are known to increase cyclic AMP, such as forskolin, VIP and PGE2 (Cuthbert et al, 1984;Cuthbert, 1990b). Potentiation was not seen with LBK and CCh and was not seen when a calcium ionophore, A23187, was used with forskolin.…”