Calcium‐and cyclic AMP‐dependent chloride secretion in human colonic epithelia

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Abstract
1 Three stable epithelial cell lines (HCA-7, HCA-7-Col 1 and HCA-7-Col 3) all derived from the same human adenocarcinoma have been cultured on collagen-coated Millipore filters. These epithelial monolayers have been used to record short circuit current (SCC) in response to a variety of secretagogues. Similar monolayers, but grown on plastic dishes, were used for measurements of tissue cyclic AMP. 2 Lysylbradykinin, applied to either side of the monolayers, increased SCC in HCA-7 cells but had little effect on the other two lines. The responses showed rapid desensitization, which could be prevented by cooling to 4°C. Responses to kinin were not significantly attenuated by piroxicam, an inhibitor of cyclo-oxygenase. 3 Other secretagogues, vasoactive intestinal polypeptide (VIP) and carbachol also increased SCC in monolayers. The responses to VIP were greatest in HCA-7-Col 1 monolayers while responses were virtually absent in HCA-7-Col 3. A similar profile was seen with carbachol except that responses of HCA-7 and HCA-7-Col 1 monolayers were more equal. With one exception the responses to VIP and carbachol showed sidedness, acting only from the basolateral side. 4 The effects of the secretagogues were inhibited by piretanide, a loop diuretic, applied basolaterally. It is presumed that SCC responses represent electrogenic chloride secretion. 5 Treatment with forskolin increased SCC in HCA-7 and HCA-7-Col 1 monolayers with little effect in HCA-7-Col 3. Nevertheless cyclic AMP levels were elevated most in HCA-7-Col 3 and least in HCA-7-Col 1 monolayers, in reciprocal relationship to the functional response. 6 A23187 increased SCC when applied to HCA-7 and HCA-7-Col 3 monolayers with little effect on HCA-7-Col 1. 7 The differential responses of the three human cell lines provide unique opportunities to discover the functional responsibilities of entities involved in the chloride secretory process. HCA-7-Col 3 cells which generate high levels of cyclic AMP in response to forskolin but which fail to show a substantial chloride secretory response may be a useful model of some disease conditions.