THE EXPRESSION OF CARBONIC ANHYDRASE-II AND ANHYDRASE-IV IN THE HUMANPANCREATIC-CANCER CELL-LINE (CAPAN-1) IS ASSOCIATED WITH BICARBONATE ION CHANNELS

Human pancreatic ductal cells of the Capan 1 cell line differentiate p rogressively during growth. After the exponential growth phase, the ce lls elongate and become polarized with their apical poles covered by m icrovilli and separated from the basolateral pole by tight junctions. In this stationary phase, they form domes, which are thought to result from the exchange of water and electrolytes. In this study, we demons trated, using patch-clamp techniques, that HCO3- ions exit via the g35 0 high conductance anionic channel we observed recently at the Capan 1 cell surface. This g350 channel was thought to be either a Cl-/HCO3- antiport or a simple HCO,- channel. The stilbene derivatives 4-acetami do-4 isothiocyano-2-2'-disulfonic acid (SITS) and 4,4' diisothiocyano stilbene-2,2' disulfonic acid (DIDS) reduced both the number of domes and the Cl- and HCO - flux through the g350 channel. Moreover, using h istochemical, immunocytochemical and biochemical methods we Showed tha t Capan 1 cells express a specific pattern of carbonic anhydrases (CA) . Two types of CA were detected: the CA II isozyme mainly localized in the cytoplasm, but also found beneath the inner leaflet of the apical plasma membrane, and the CA IV isozyme localized on the outer leaflet of the apical plasma membrane and microvilli. Their molecular masses were 30 (CA II) and 55 kDa (CA IV), respectively. They were expressed continuously during the exponential growth phase, although their activ ity increased greatly during the stationary phase. Inhibition of dome formation by acetazolamide indicated the existence of a direct relatio nship between dome formation and CA. Characteristic structures with a central electron-dense core surrounded by a light halo were observed o n the surface of cell membranes using histochemical and immunocytochem ical methods. These structures were thought to represent a channel, co rresponding possibly to CA IV. Our observations suggest that Capan 1 c ells, despite their neoplasic transformation, produce HCO3- ions in th e same way as normal human pancreatic ductal cells. Capan 1 cells in c ulture may therefore represent a suitable model for studying pancreati c duct HCO3- secretion at the cellular and molecular levels.