Sulfonylurea-sensitive K⁺ transport is involved in Cl^- secretion and cyst growth by cultured ADPKD cells

Transepithelial chloride and fluid secretion by many types of epithelia involves activation of a conductive K+ pathway that serves to support the electrochemical driving force for Cl^- secretion. This study sought to determine if such a pathway is involved in Cl^- and fluid secretion by the cystic epithelia in autosomal dominant polycystic kidney disease (ADPKD). Primary cultures of cells derived from the cysts of patients with ADPKD were used. Confluent monolayers of these cells, mounted in Ussing chambers, were stimulated to secrete Cl^- by application of the adenylyl cyclase agonist, forskolin. The effects of various K⁺ channel blockers on the increase in short-circuit current (I_sc) generated by active Cl^- secretion were determined. Charybdotoxin, an inhibitor of Ca²⁺-sensitive K⁺ channels exerted no effect. Similarly, the chromanole 293B, an inhibitor of cAMP-induced K⁺ conductance, exerted no effect on cAMP-dependent anion secretion. Glibenclamide, an inhibitor of ATP-sensitive K⁺ channels and the cystic fibrosis transmembrane conductance regulator (CFTR), modestly inhibited the forskolin-stimulated current when applied to the apical surface of the monolayers, suggesting a relatively weak effect on CFTR. Basolateral application of glibenclamide inhibited I_sc to a greater extent. This latter effect may be due to inhibition of a K⁺-conductive transport step. Glibenclamide exerted little effect on the I_sc of nonstimulated monolayers. Cyst growth in ADPKD is driven by cell proliferation and Cl^- and fluid secretion. The effect of glibenclamide on the growth of cysts formed within a collagen gel by cultured ADPKD cells was tested. Addition of glibenclamide to the media bathing the cysts inhibited their growth. Glibenclamide also blocked the formation of cysts when it was added to the media at the time the cells were seeded within the collagen gel. Glibenclamide was also found to inhibit the proliferation of ADPKD cells. RT-PCR analysis demonstrated that the ATP-sensitive K⁺ channel, K_ir 6.2, is expressed in cultured ADPKD cells and in normal human kidney. These results suggest that ATP-sensitive K⁺ channel blockers should be investigated as possible therapeutic agents to inhibit cyst growth in ADPKD.